POTATO FERTILIZER EXPERIMENTS IN CALIFORNIA O. A. LORENZ J. C. BISHOP B. J. HOYLE M. P, ZOBEL P. A. MINGES L D. DONEEN A. ULRICH :! ; IFORNIA AGRICULTURAL >ERIMENT STATI — POTATOES are one of the most important vegetable crops in Cali- fornia, about 120,000 acres being planted annually. During the past 15 years a tremendous increase in acreage has oc- curred in the early producing areas, centered chiefly in the southern San Joaquin Valley. RESULTS of approximately 80 fertilizer experiments on potatoes in all the important producing areas of California are here pre- sented. These experiments have been conducted since 1937 and are still continuing. They deal with rates and sources of many nitrogenous materials and rates of application for phos- phoric acid and potash. The value of liquid fertilizers applied to the soil and to the plant has been investigated, as well as time of application and placement of fertilizers. In addition to yield, the effect of fertilizers on grade, keeping quality, and nutrient composition is given. THIS BULLETIN will serve as a guide for growers in fertilizing their potato crops. It will be useful also to Farm Advisors, research workers, and the fertilizer industry, giving results from new techniques such as liquid and gaseous injected fertilizers and spray fertilizers not previously available. Pages 3 to 7 tell how, where, and when the work was done. Pages 8 to 20 give county-by-county reports of rates of N, P 2 5 , and K 2 on yields. Pages 20 to 43 discuss other results related to potato fertilization. THE AUTHORS: O. A. Lorenz is Associate Professor of Vegetable Crops and Associate Olericulturist in th< Experiment Station, Davis. J. C. Bishop is Associate Specialist in the Department of Vegetable Crops, Davis. B. J. Hoyle is Associate Specialist in the Field Station Administration, Tulelake. M. P. Zobel is former Assistant Specialist in the Department of Vegetable Crops, Davis. P. A. Minges is Agriculturist in Agricultural Extension, Davis. L. D. Doneen is Professor of Irrigation and Irrigationist in the Experiment Station, Davis. A. Ulrich is Associate Plant Physiologist in Plant Nutrition in the Experiment Station, Berkeley. OCTOBER, 1954 POTATO FERTILIZER EXPERIMENTS IN CALIFORNIA* O. A. LORENZ M. P. ZOBEL L D. DONEEN J. C BISHOP B. J. HOYLE P. A. MINGES A. ULRICH How, where, and when the experiments were conducted ... a summary of results Producing areas and soils Potato production in California is cen- tered in several distinct districts. The southern San Joaquin Valley area in- cludes the counties of Kern, Tulare, Ma- dera, and Fresno and comprises about two thirds of the entire state acreage. Most of this area is devoted to the early spring crop, which is planted from De- cember to March and matures from May to July. The soils used for potato growing in this area are classified chiefly as fine sandy loams. Some of them are very sandy and contain only a small amount of silt. They are alkaline and often slightly calcareous. They are low in or- ganic matter and nitrogen and are very subject to leaching of plant nutrients such as nitrogen because of their light texture. Potatoes are not grown in any regular cropping system but are usually planted in rotations with cotton, alfalfa, barley, or sugar beets. Because of the build-up of scab, successive crops of potatoes are not usually grown on the same soil. In Riverside and San Bernardino coun- ties potatoes are grown chiefly for late spring and summer production. The soils are sands and sandy loams and are alka- line in reaction. They are low in organic * Submitted for publication January 13, 1954. matter and nitrogen but are fairly well supplied with the mineral nutrients. The Tulelake district comprises parts of Modoc and Siskiyou counties in north- ern California. The crop is planted chiefly in May, harvested during early fall, and stored for shipment during the winter months. The soils vary from fairly deep peats near the center of the old lake bot- tom to fine sandy loams and sands on the fringes of the old lake. Many of the or- ganic soils contain volcanic ash and are unlike most organic soils in that they are well supplied with mineral nutrients such as phosphorus and potassium. Potatoes in the Delta area of Central California are grown chiefly in San Joa- quin and Contra Costa counties. Most of the crop is planted in late spring and harvested from July to November. Pro- duction is limited almost entirely to deep peat soils, which are acid and inherently low in phosphorus and potassium. They are also low in available nitrogen. The potatoes are usually grown in a cropping system involving the high-value cash crops, such as sugar beets, celery, onions, field corn, and barley. Some of the smaller production dis- tricts in California include the Santa Maria Valley in Santa Barbara County and areas in the counties of San Diego, Los Angeles, Sonoma, and Monterey, 3] where the potatoes are grown chiefly for local consumption or for chips. There is also some production in the mountain areas of Modoc, Lassen, and Inyo coun- ties. The stage of maturity at which the po- tatoes are harvested varies greatly in the different areas. In Kern, Tulare, Madera, and other early producing areas the pota- toes are often harvested immature and in many cases when they are still growing actively. The vines may still be green, and the tubers may skin badly at digging time. In the Delta and Coastal areas the potatoes are usually fully mature at dig- ging. The vines have died and the skin has set on the tubers. At Tulelake, growth in the fall may be terminated by frost; however, the tubers are left to mature fully before digging. Previous fertilizer experiments It has long been recognized that pota- toes grown in California give large in- creases in yield when supplied with commercial fertilizers, particularly nitro- gen. Results of some early fertilizer ex- periments on potatoes were summarized by Porter in 1932 and Schneider in 1939 (See "Literature Cited" on page 46). Since their reports, the areas of produc- tion have changed greatly. On the basis of experiments reported by Porter and Schneider for sandy soils in Kern County, the recommendation was to ap- ply from 400 to 800 pounds of ammo- nium sulfate per acre. The results from other sources of nitrogen were not con- clusive, and phosphoric acid and potash applications were shown to be of no benefit. Tests on sandy soils in Riverside County had shown marked increases in yield from ammonium sulfate fertiliza- tion and possibly small increases from phosphoric acid, but none from potash. In Los Angeles County trials, potato yields were increased by the application of nitrogenous fertilizers but not by phos- phoric acid. Lindsay and Longfellow in 1937 reported on the results of fertilizer 1. Precision fertilizer hoppers mounted on Iron Age potato planter. This machine was used in many of the tests described in this bulletin. [4] experiments in Kern County. Their re- sults showed yield increase from ammo- nium sulfate fertilizer from applications as high as 160 pounds of nitrogen per acre. How the experiments were conducted Most of the experiments were con- ducted in commercial fields in coopera- tion with members of the Agricultural Extension Service and the growers. The growers' practices were followed except for fertilization. Some of the experiments were located at the U. S. Cotton Field Station at Shafter, California, and at the University of California Field Station at Tulelake. In all tests the fertilizers were applied with special experimental machines (See "Literature Cited," Fairbanks and Minges, 1942) , or by the use of precision hoppers mounted on an Iron Age as- sisted-feed potato planter, shown on page 4. In some experiments the fertilizers were applied as a single band 2 inches to one side and 2 inches below the seed piece. In most experiments in Kern and Tulare counties, the fertilizers were ap- plied in two bands 2 inches to each side and 2 inches below the seed piece at the time of planting. Plots were usually either 2 or 4 rows wide, each row being from 100 to 125 feet long. In the 4-row plots, the two out- side rows were often used as guards, al- though experiments conducted on these sandy soils have given identical results whether or not guard rows were included. The tests were laid out in a randomized block design, with from four to six plots of each fertilizer treatment. The row spacing varied from 28 inches in some of the San Joaquin Delta plots to 32 inches in the southern San Joaquin Valley tests and to 38 inches or wider at Tulelake. The plants in the row were spaced from 7 to 12 inches apart; and from 15 to 20 sacks of seed were planted per acre. All data were analyzed statistically. The irrigation practice varied consid- erably in the different areas. In the Tulare, Fresno, and Kern county experi- ments, the potatoes usually received daily irrigations in alternate furrows, from the time the plants were about 6 inches tall until a few days before harvest. In Ma- dera County somewhat fewer irrigations were applied. In the Tulelake area the potatoes usually received a total of 10 to 13 furrow irrigations as required. In the Delta area the potatoes were irrigated by the subirrigation method, where a more or less constant water level was main- tained during the growing season. The potatoes were harvested with com- mercial diggers and picked up by hand; and the total weight per plot was taken directly in the field. In some tests the tubers were graded at a packing shed as is the commercial practice, while in oth- ers they were hand-graded and sized by the use of sizing rings. In most tests only the total yield was determined, since it has been shown that the total yield and the yield of U. S. No. l's are very highly correlated. Samples of tubers or other plant mate- rial from the various fertilizer plots were used for the chemical analyses presented in this bulletin. Likewise the tubers har- vested from these plots were used to de- termine the effect of fertilizers on specific gravity, grade, and storability. Here is a summary of the results Detailed analyses of specific results are given in the sections following this. Nitrogen was the nutrient most closely associated with increased yields, in the more than 80 experiments con- ducted over a period of 16 years in all the important producing areas of the state. On the sandy and sandy-loam soils of the San Joaquin Valley and in south- ern California, responses in yield were common with nitrogen applications up to 120 pounds per acre. Higher applications to as high as 150 pounds or more per [5] 400 i50 •00 O 250 o 200 150 100 San Joaquin County (9 tests) \ # — - " Tulelake Area (7 tests) st <^~ — *~~ « Kern County S ^^^ (II tests) -yS ^^ Madera County (4 tests) ^/\s^ Tulare County >^^ (8 tests) - ^s^ Fresno County ^^^ (3 tests) - — / - r i 1 1 1 1 1 30 60 90 120 150 180 POUNDS OF NITROGEN APPLIED PER ACRE Fig. 2. Rates of nitrogen application and yield of potatoes for some of the important California growing areas. acre were often beneficial. On peat soils of the San Joaquin Delta area, yield in- creases were obtained with nitrogen ap- plications of up to 160 pounds per acre. On organic soils at Tulelake there was practically no benefit from nitrogen ap- plications higher than 60 pounds per acre. Phosphorus was associated with small average increases in yield in tests on sandy soils in Kern, Tulare, and Fresno counties. In some tests very large increases in yield were obtained. On peat soils in San Joaquin County there was little increase from applications above 80 pounds of phosphoric acid per acre. On peat soils at Tulelake small yield in- creases were obtained, but there seemed to be no benefit from applications of more than 60 pounds of phosphoric acid per acre. Some of the mountain and coastal soils were very deficient in phos- phorus. Potash applications gave increases in yield on peat soils of the San Joaquin Delta, and often applications as high as 160 pounds per acre were needed. The organic soils at Tulelake showed no re- sponse to potash fertilization. The only mineral soils showing benefit from pot- [6] ash application were those of the Ripper- dan series located south of the town of Madera. Source-of-nitrogen experiments on sandy-loam soils in Kern County showed the superiority of ammonium sources. Calcium nitrate, sodium nitrate, and urea all produced yields considerably below those obtained with ammonium sulfate. Ammonium nitrate yielded better than straight nitrate sources but poorer than ammonium sulfate. Natural organics such as dried blood also produced yields slightly below ammonium sulfate. These results will probably apply to sandy soils in other areas of the state. Ammonium sulfate, ammonium hy- droxide (aqua ammonia), urea, and so- dium nitrate applied in the irrigation water at plant emergence produced yields lower than those obtained with ammo- nium sulfate applied in the bed 2 inches below and 2 inches to each side of the seed piece at planting. Liquid nitrogen materials applied in the irrigation water at plant emergence or later showed little benefit from applications made later than 6 weeks after plant emergence. Supplemental soil injections of anhy- drous ammonia made at the time of plant emergence produced yields as good as those obtained from supplying all of the nitrogen from ammonium sulfate at planting. Nitrogen sprays using urea were of practically no benefit on potatoes grown in Kern County. With fertilizer applications made 2 inches to both sides of the seed piece, placements made level with or slightly below the seed produced higher yields than those 2 inches above or nearly 4 inches below the seed piece. Fertilizers producing the highest total yield always produced the highest yield of both U. S. No. 1 and U. S. No. 2 potatoes per acre. The percentage of po- tatoes in the No. 2 grade was usually highest from treatments producing the highest total yield, because of an increase in knobs, growth cracks, and sunburn. The percentage of No. 1 potatoes was seldom affected by fertilizer treatment except when the total yields of unfertil- ized plots were very low. In these cases the tubers had not reached sufficient size to place them in the U. S. No. 1 size A grade. In Madera County tests the loss of moisture by tubers in storage was not in- fluenced by any of the fertilizer treat- ments. At Tulelake there was no relation between fertilizer application and storage losses due to moisture, rots, or sprouting. Soluble nutrient analyses of petiole tissue made from 4 to 6 weeks after plant emergence suggested that plants should contain a nutrient level of at least 800 parts per million of nitrate nitrogen, 50 of phosphorus, and 6,000 of potash, ex- pressed on a fresh-weight basis for maxi- mum yields. Nutrient contents much lower than these were usually associated with decreased yields. Specific gravity and percentage dry weight of tubers was usually, but not always, lower in potatoes receiving high nitrogen applications than in those re- ceiving low rates of nitrogen or none. This was usually associated with earlier maturity of the low-nitrogen fertilized potatoes. The percentage of nitrogen and phos- phorus in the tubers was usually in- creased by the application of these nutri- ents. The potassium content of the tubers varied only slightly, even in tests where there were pronounced yield responses from potash fertilization. Over four fifths of the growth of the potato plant occurred from 60 to 120 days after planting. There was little tuber growth earlier than 60 or 70 days after planting. A potato crop yielding about 300 sacks per acre removed from the soil about 150 pounds of nitrogen, 35 of phosphoric acid, and 250 of potash. The tubers ac- counted for the removal of from 60 to as high as 90 per cent of the total. [7] Here is a counfy-by-county report on rates of fertilizer on yields Fertilizers and the yields of potatoes The yield data for the many fertilizer experiments are summarized chiefly by counties. The pertinent data for each test — such as soil type, the nearest town, and the planting and harvest dates — are presented as a portion of the tables giv- ing the yield data for the particular tests. Unless otherwise specified, nitrogen was derived from ammonium sulfate or 16- 20 ammonium phosphate-sulfate, phos- phoric acid from treble superphosphate or 16-20 ammonium phosphate-sulfate, and potash from potassium sulfate. KERN COUNTY Most of the experiments in Kern Coun- ty* were conducted on Hesperia fine sandy loam soils at or near the U. S. Cot- ton Field Station at Shafter. Soils belong- * These experiments were conducted in co- operation with D. N. Wright and M. L. Lindsay, Farm Advisors, Agricultural Extension Service, and G. A. Harrison and E. G. Smith of the U. S. Department of Agriculture. ing to this series are very productive, and many of the potatoes in the Shafter- Wasco area are produced on it. Different fields were used for the tests each year. The potatoes were usually planted in early February and harvested from June 5 to June 20. Ammonium sulfate was used as the source of nitrogen and was applied 2 inches to the side and 2 inches Table 1. Total Yields in Hundredweights Per Acre of White Rose Potatoes Using Increasing Rates of Ammonium Sulfate Fertilizer 1 1 -Years Results at the U. S. Cotton Field Station, Kern County Nitrogen applied (pounds per acre) Year of test Av. 1940 1941 1942 1944 1945 1946 1947 1948 1949 1952 1953 None Yields in hundredweights per acre 146 279 300 321 330 140 318 330 359 349 233 382 412 425 398 97 195 240 231 131 239 261 280 165 314 375 404 205 371 390 422 248 339 362 268 396 468 465 103 219 260 263 131 297 380 385 400 170 301 341 356 50 or 60 100 or 120 150 or 160 200 L.S.D.5% level 40 36 31 28 50 46 66 44 43 17 40 18 [8] Table 2. Total Yields in Hundredweights Per Acre of White Rose Potatoes from 10 Tests Comparing Nitrogen, Phosphoric Acid, and Potash Fertilizers U. S. Cotton Field Station, Kern County Year of test Nutrients applied* 1937 1938 1939 1940 1941 1942 1944 1945 1946 1947 Av. Yields in hundredweights per acre N 301 304 300 313 339 340 359 404 410 291 316 330 347 375 349 382 412 398 240 224 248 261 305 314 375 395 431 422 471 477 329 N +P 2 5 354 N +P 2 5 +K 2 360 L. S.D.5%level. ... 25 26 20 40 36 31 28 50 46 66 13 Nitrogen was supplied from ammonium sulfate at rates of 100, 120, or 150 pounds of N per acre. Phosphoric acid was supplied from treble superphosphate at rates of 125 or 180 pounds of P2O5 per acre. Potash was derived from potassium sulfate and supplied at rates of 125 or 150 pounds of K2O per acre. below the seed piece. Data showing the response to nitrogen are presented in table 1. On page 8 are summarized the data for nitrogen responses for these ex- periments, along with those conducted in the other counties where a large number of tests were conducted. Since the same rates of nitrogen were not used in all tests, the tests are grouped for nitrogen applications of 50 or 60 pounds per acre, 100 or 120 pounds per acre, and 150 or 160 pounds per acre. The yield was nearly doubled by nitro- gen applications of 50 or 60 pounds per acre. Further responses were noted as the application was increased from 50 or 60 to 100 or 120 pounds. The data show a general trend of small increases in yield beyond the 120-pound rate, though none of the differences are individually sig- nificant. In five of the eleven tests the 150 or 160-pound per acre application in- creased the yield by more than 20 sacks per acre over the 100 or 120-pound rates. No benefit was noted as the application was increased from 160 to 200 pounds of nitrogen per acre. The responses to phosphoric acid and potash for experiments conducted on the Hesperia fine sandy loam soils are shown in the data in table 2. Whenever the re- sponse to phosphoric acid was tested, it was in the presence of liberal amounts of nitrogen supplied from ammonium sul- fate. The actual amount of nitrogen was not held constant in all of the tests but varied from 100 to 150 pounds per acre. Phosphoric acid was derived from treble superphosphate and was tested at fairly high rates of 125 or 180 pounds of P 2 0, per acre. Potash was tested in the pres- ence of both nitrogen and phosphoric acid and was supplied from potassium sulfate at rates of 125 or 150 pounds of K 2 per acre. An average of ten tests conducted from 1937 to 1947 show that phosphoric acid in addition to nitrogen increased the yield from 329 to 354 sacks per acre, an increase of about 8 per cent. In eight of the ten tests, phosphoric acid increased the yield by 20 or more sacks per acre; and in four of the tests the yield was increased by more than 40 sacks. Applying potash in addition to nitrogen and phosphoric acid did not significantly increase the yield above that obtained with nitrogen and phosphoric acid alone. [9] Table 3. Total Yields in Hundredweights Per Acre of White Rose Potatoes from Fertilizer Tests Conducted in 3 Potato- Growing Districts of Kern County Nutrients applied (pounds per acre) Location of test Saco* Edison f Wheeler Ridge J N P2O5 K2O Yields in hundredweights per acre 174 251 323 258 253 127 211 239 222 245 108 102 102 281 267 60 120 120 150 120 150 150 L. S.D. 5% level 80 60 49 * Sill ranch, Adelanto loamy sand; planted 1/30/42, harvested 6/4/42. t Irving Williams, Edison sandy loam; planted 1/22/44, harvested 5/25/44. t Charles West, San Emigdio sandy loam; planted 3/9/48, harvested 6/30/48. Data for three other experiments con- ducted in Kern County are presented in table 3. In an experiment on Adelanto loamy sand there was a marked increase in yield as nitrogen was increased from none to 60 pounds per acre, but there was no definite increase as the nitrogen level was raised from 60 to 120 pounds per acre. The application of phosphoric acid and potash did not produce in- creased yields. In an experiment on an Edison sandy loam there was a pronounced increase in yield as the nitrogen was raised from none to 60 pounds per acre, but only a small increase resulted from nitrogen applications above this figure. Phos- phoric acid and potash applications had no effect on yield. In the test on a San Emigdio sandy loam soil at Wheeler Ridge, the yield was more than doubled by the applica- tion of phosphoric acid. Potash applica- tions had no effect on yield. These sandy soils also require very high applications of nitrogen; but the response to nitrogen could not be measured in this test since the different rates were not supplied in the presence of phosphoric acid, which was also very deficient. [10] COUNTY The Tulare County experiments" were conducted chiefly on soils of the Hes- peria series (table 4). The results agree fairly well with those obtained at Shafter with soils of this same series. In all of the eight experiments conducted, there was a very pronounced increase in yield as the nitrogen application was increased from none to 50 pounds per acre. In * These experiments were conducted in co- operation with Vincent Schweers, Farm Ad- visor, and Walter Cordua, formerly Farm Advisor, Agricultural Extension Service. seven of the tests further increases in yield were noted as the nitrogen applica- tion was increased from 50 to 100 pounds per acre, but applying 150 pounds per acre produced yields practically equal to those obtained with 100 pounds. There were indications of a slight response to phosphoric acid, and in four of the eight tests the plots receiving phosphoric acid yielded over 20 sacks per acre more than did those where it was not applied. Pot- ash applications had no effect on yield or on visible plant growth. Table 4. Total Yields in Hundredweights Per Acre of White Rose Potatoes for 8 Fertilizer Tests Conducted in 3 Potato- Growing Districts of Tulare County r Nutrients applied (pounds per acre) Location of test Av. (1) Porter- ville (2) Earli- mart (3) Earli- mart (4) Earli- mart (5) Pixley (6) Earli- mart (7) Pixley (8) Earli- mart N P2O5 K-O Yields in hundredweights per acre 118 215 70 231 118 160 120 215 156 50 234 286 86 376 279 252 153 318 248 100 272 268 128 404 340 303 181 350 281 150 288 276 105 406 368 324 180 348 287 150 150 262 260 139 461 412 302 214 367 302 150 150 150 272 152 435 395 345 194 365 150 50 291 299 198 358 L.S.D. 5% level 40 65 37 72 31 39 44 22 36 Col. (1) (2) (3) (4) (5) (6) (7) (8) A. H. Cameron & Sons, Hanford loamy fine sand; planted 3/15/49 Lester Kiggens, Hesperia loam; planted 4/12/49, harvested 7/11/4 Lester Kiggens, Hesperia loam; planted 3/7/50, harvested 7/5/50. Lester Kiggens, Hanford sandy loam; planted 2/6/51, harvested 7/ Ben Lapadula, Tujunga sand and Hesperia sandy loam; planted 3/ Lester Kiggens, Hesperia loam; planted 2/21/52, harvested 6/18/5 Ben Lapadula, Hesperia loam; planted 3/6/52, harvested 7/3/52. Lester Kiggens, Hesperia loam; planted 3/16/53, harvested 7/16/5 , harvested 7/12/49. 9. 2/51. 15/51, harvested 7/9/51. 2. 3. [11] COUNTY The experiments in Madera County* were conducted on sandy loam soils of the Hanford and Ripperdan series. Pota- toes grown on plots that did not receive nitrogen yielded higher than those in most other tests where they were grown on the sandy Central Valley soils (table 5). Even so, the yield was increased markedly as the nitrogen application was increased from none to 50 and from 50 to 100 pounds per acre. There was little * These experiments were conducted in co- operation with C. E. Johnson, Farm Advisor; and B. S. Gould and R. J. Gotelli, formerly Farm Advisors, Agricultural Extension Service. change in yield as the nitrogen was in- creased from 100 to 150 pounds per acre. The application of phosphoric acid in addition to nitrogen did not increase the yield beyond that obtained with nitrogen alone. In all tests conducted on the Rip- perdan fine sandy loam soils, there was a large increase in yield from the applica- tion of potash fertilizer. In 1950 this in- crease was almost 100 sacks per acre, and in 1951 nearly 70 sacks per acre. These soils of the Ripperdan series have been the only mineral soils that have given responses in yield from potash application. Table 5. Total Yields in Hundredweights Per Acre of White Rose Potatoes from 6 Fertilizer Tests Conducted on Two Soil Types Near Madera, Madera County Soil series Nutrient applied (pounds per acre) (1) Hanford (2) Ripperdan (3) Hanford (4) Ripperdan (5) Hanford (6) Ripperdan Av. N P 2 5 K 2 Yields in h undredweights per acre 220 247 171 166 201 50 283 283 205 223 249 100 329 351 196 271 287 150 390 324 196 290 300 L.S.D.5%level 47 150 390 324 196 290 308 308 303 150 150 393 342 195 283 341 296 308 150 150 150 387 388 191 381 383 365 349 L.S.D.5%level 91 59 19 34 53 39 32 Col. (1): Charles Haire, Hanford fine sandy loam; planted 3/2/49, harvested 7/5/49. (2): S. Frank Martin, Ripperdan fine sandy loam; planted 2/22/49, harvested 6/20/49. (3): Charles Haire, Hanford fine sandy loam; planted 3/1/50, harvested 6/19/50. (4): S. Frank Martin, Ripperdan fine sandy loam; planted 2/23/50, harvested 6/9/50. (5) : Weis Bros., Hanford fine sandy loam; planted 3/1/51, harvested 7/3/51. (6): S. Frank Martin, Ripperdan fine sandy loam; planted 3/2/51, harvested 6/22/51. [12] FRESNO COUNTY These experiments* were conducted on very light sandy soils of the Fresno and Dinuba series (table 6). All of the tests were near the town of Conejo. Large in- creases in yield were noted as the nitro- gen application was increased from none to 50 or 100 pounds per acre. Applying 150 pounds of nitrogen per acre pro- duced over 25 sacks per acre more than * These experiments were conducted in co- operation with D. N. Wright, Farm Advisor, and E. E. Saunders, formerly Farm Advisor, Agricultural Extension Service. was harvested from plots receiving only 100 pounds of nitrogen per acre. In all of the tests, plots that received the complete fertilizer yielded higher than those receiving only nitrogen. Foli- age growth was also increased. The re- sponse in addition to nitrogen was probably due only to phosphoric acid and not to potash, since the phosphorus con- tent of the plants was greatly increased as compared to those receiving only nitro- gen, and there was no difference in the potassium content. Table 6. Total Yields in Hundredweights Per Acre of White Rose Potatoes from 3 Fertilizer Tests Conducted Near Conejo, Fresno County Nutrients applied (pounds per acre) Location of test Av. (1) Conejo (2) Conejo (3) Conejo N P2O5 K 2 Yields in hundredweights per acre 62 151 191 234 255 208 242 266 292 316 113 187 218 234 264 250 128 193 225 253 278 50 100 150 150 150 150 150 100 L. S. D. 5% level 7 47 65 35 Col. (1): Ed Loescher, Fresno sand; planted 2/17/45, harvested 6/22/45. (2): Ed Loescher, Fresno sand; planted 2/19/45, harvested 6/22/45. (3): R. H. Mitchell, Dinuba sand; planted 2/26/46, harvested 7/6/46. [13] RIVERSIDE COUNTY Since previously reported experi- ments* (Porter and Schneider) had shown marked responses to nitrogen fer- tilization, these tests were designed to * These experiments were conducted by W. B. Gardner, formerly Farm Advisor, Agricul- tural Extension Service. measure the response only to phosphoric acid and potash applied in conjunction with liberal applications of nitrogen. The data, reported in table 7, show that no increase in yield was obtained by applica- tion of phosphoric acid or potash, be- yond that obtained with nitrogen alone. Table 7. Total Yields in Hundredweights Per Acre of White Rose Potatoes from 6 Tests Comparing Phosphoric Acid and Potash Fertilizers on Both Spring and Fall Crops Grown in Western Part of Riverside County Location of tests Nutrients applied (pounds per acre) (1) Romoland (2) Nuevo (3) Perris (4) Moreno (5) Winchester (6) Nuevo Av. N P 2 Os K2O Yields in hundredweighl s per acre 160 419 214 282 476 306 516 369 160 50 444 215 290 446 296 547 373 160 100 497 221 290 447 289 531 379 160 200 432 226 291 461 305 528 374 160 100 100 428 227 298 443 300 527 370 L.S.D.5%level 21 Col. (1): Charles Motte, Ramona sandy loam; planted 3/4/47. (2) : Smith Bros., Hanford sandy loam; planted 8/1/47. (3): Ira Clark, Ramona sandy loam; planted 8/4/47. (4): Hendrick Ranch, Ramona sandy loam; planted 3/5/48. (5): Fred McCall, Ramona sandy loam; planted 3/12/48. (6): Norman Walker, Hanford sandy loam; planted 4/1/48. [14] COUNTY In experiments near Chino,* San Ber- nardino County, in 1947 on a Hanford sandy loam soil, comparisons were made of applications of 100 and 200 pounds of nitrogen per acre from ammonium sul- fate. The yield from the 100-pound-per- * These experiments were conducted by G. H. Bowman, Farm Advisor, Agricultural Exten- sion Service, and Glen Livingston, Grower, Chino, California. acre rate was 347 sacks per acre, as com- pared with 356 sacks for the 200-pound rate. The application of phosphoric acid in addition to nitrogen did not increase the yield above that obtained with nitro- gen alone. In a test repeated on the same farm in 1948, 100 pounds of nitrogen per acre produced yields of 235 sacks per acre, as compared to 247 for 180 pounds of nitrogen. LES COUNTY An experiment* was conducted on a Hanford fine sandy loam soil near New- hall in 1946. The yield was increased from 239 on the plots lacking nitrogen to 369 sacks for those receiving 80 pounds of nitrogen per acre. Increasing the nitro- * Conducted in cooperation with H. W. Schwalm, Farm Advisor, Agricultural Exten- sion Service, and Jess Butler, grower, Newhall, California. gen level to 160 pounds per acre pro- duced a yield of 415 sacks, but applying 240 pounds of nitrogen per acre did not increase the yield above that obtained with 160 pounds. In the presence of 160 pounds of nitro- gen per acre, the application of phos- phoric acid and potash did not increase the yield above that obtained with nitro- gen. [ 15 ] JOAQUIN COUNTY The experiments in San Joaquin Coun- ty*"' were conducted on deep peat soils of the Venice and Staten series. Most of these soils have for many years been utilized for the production of potatoes, celery, sugar beets, and other cash crops and have received liberal amounts of complete fertilizers. The results of nine * These experiments were conducted in co- operation with J. P. Underhill, Farm Advisor, Agricultural Extension Service. More complete results were published in University of Cali- fornia Truck Crops Mimeo. No. 54, April, 1952. experiments conducted during the years 1948 to 1950 are presented in table 8. This was the only area in the state where responses to all three nutrients were ob- tained. An average of all tests shows that the highest yields were obtained from applications of 160 pounds per acre each of nitrogen, phosphoric acid, and potash. Individual tests varied greatly in the yield responses, particularly to nitrogen and potash. In some of the tests the omis- sion of either of these nutrients resulted in very poor and unacceptable yields. Table 8. Total Yields in Hundredweights Per Acre of White Rose Potatoes from 9 Fertilizer Tests on Peat Soils of the San Joaquin County Delta District Nutrients applied (pounds per acre) Location of test Av. (1) Mc- Donald Island (2) Mc- Donald Island (3) Termi- nous (4) Mc- Donald Island (5) Mc- Donald Island (6) Mc- Donald Island (7) Mc- Donald Island (8) Termi- nous (9) Bacon Island N P2O5 K2O Yields in hundredweights per acre 284 325 149 293 465 240 314 296 160 160 404 387 194 261 201 322 505 249 402 325 80 160 160 380 466 254 344 310 320 499 320 376 363 160 160 160 402 492 303 401 325 348 504 290 391 384 160 160 373 456 247 391 315 299 494 273 316 352 160 80 160 407 464 275 410 319 316 524 317 351 376 160 160 293 374 220 359 246 301 447 240 370 317 160 160 80 357 452 275 373 277 331 450 296 354 352 L.S.D.5%level 43 77 54 39 53 N.S. N.S. 46 36 28 Col. (1) (2) (3) (4) (5) (6) (7) (8) (9) Zuckerman Farms Co., Venice peaty muck; planted 3/22/48, harvested 8/18/48. Zuckerman Farms Co., Staten peaty muck; planted 3/30/48, harvested 9/10/48. Atkins-Kroll Co., Staten peaty muck; planted 6/24/48, harvested 11/24/48. Zuckerman Farms Co., Venice peaty muck; planted 3/26/49, harvested 8/6/49. Zuckerman Farms Co., Venice peaty muck; planted 4/1/49, harvested 8/24/49. Zuckerman Farms Co., Venice peaty muck; planted 3/20/50, harvested 7/31/50. Zuckemran Farms Co., Venice peaty muck; planted 3/27/50, harvested 10/2/50. Atkins-Kroll Co., Staten peaty muck; planted 6/22/50, harvested 12/19/50. Gay Rible, Staten peaty muck; planted 4/7/50, harvested 9/7/50. [16] The average yield for the nine tests for the plots lacking nitrogen was 325 sacks per acre, as compared with 363 and 384 sacks for plots receiving 80 and 160 pounds of nitrogen per acre, respectively. In five of the nine experiments, plots re- ceiving 80 pounds of nitrogen per acre had higher yields than those without any, while in the other tests they were about equal. In four tests, the plots receiving 160 pounds of nitrogen per acre had higher yields than those receiving only 80 pounds. The average for all of the tests showed that the non-phosphate-fertilized plots yielded 352 sacks per acre, as compared to 376 and 384 sacks for treatments re- ceiving 80 and 160 pounds of phosphoric acid per acre, respectively. In eight of the nine tests, plots receiving 80 pounds of phosphoric acid yielded higher than those not receiving this nutrient, even though the overall response to phosphate fer- tilization was quite small. Plots lacking potash yielded an aver- age of 317 sacks per acre, while the yield of those receiving 80 pounds of potash per acre was 352 sacks per acre, and 374 sacks resulted from the 160-pound per acre application. In seven of the nine tests, the yield for the 80-pound-per-acre potash application was higher than for those lacking this nutrient, and in six tests the yield for treatments receiving 160 pounds per acre was greater than for 80 pounds. ELAKE AREA The results from seven experiments conducted in the Tulelake area* are pre- sented in table 9. High yields were pro- duced even without the application of any of the nutrients. Nitrogen was the nutrient found most likely to be deficient, and in all of the tests higher yields were produced on plots receiving 60 pounds or more of nitrogen per acre than on plots not receiving nitrogen. An average of all tests shows that no-nitrogen plots yielded 290 sacks per acre, as compared to 351 sacks for those receiving 60 pounds of nitrogen per acre. In only two tests was there indication that applying 120 pounds of nitrogen resulted in higher yields than those obtained with 60 pounds. The application of phosphoric acid and potash in addition to nitrogen did not * Some of these experiments were conducted in cooperation with K. G. Baghott and M. V. Maxwell, Farm Advisors, Agricultural Exten- sion Service. increase the yield beyond that obtained with nitrogen alone. In addition to experiments in the out- lying Tulelake area, six experiments were conducted at the University of Cali- fornia Tulelake Field Station, located just east of the town of Tulelake. These experiments have been superimposed each year on plots that received the same fertilizer treatment in previous years. The results averaged for the 6-year period (table 10) show that nitrogen ap- plications of 60 pounds per acre pro- duced significant increases in yield. The application of 60 or 120 pounds of phos- phoric acid per acre produced higher yields than no phosphorus application, although only the higher rate was statis- tically significant. The application of pot- ash in addition to nitrogen and phos- phoric acid did not increase the yield above that obtained with these latter nutrients alone. The plants fertilized with nitrogen [17] Table 9. Total Yields in Hundredweights Per Acre of Two Varieties of Potatoes from 7 Fertilizer Tests Conducted in the Tulelake Basin, Siskiyou, and Modoc Counties Nutrients applied (pounds per acre) Variety Av. (1) Russet Burbank (2) White Rose (3) White Rose (4) Russet Burbank (5) White Rose (6) White Rose (7) Russet Burbank N P2O5 K2O 120 . . . . Yields in hundredweights per acre 147 237 265 285 277 465 356 290 60 120 . . . . 194 319 319 408 294 492 431 351 120 120 .... 194 343 346 408 306 479 433 358 120 . . . . 195 328 341 368 331 476 408 350 120 60 . . . . 219 319 370 398 305 507 406 361 120 120 120 .... 203 329 350 434 298 493 429 362 L. S. D. 5% level 36 40 N.S. 59 N.S. N.S. 35 21 Col. (1): Ed Sens, organic; planted 5/24/49, harvested 9 23 49. (2): Erwin Shoemaker, organic; planted 5/22/49, harvested 10/2/49. (3): Tex Barrett, organic; planted 5/10/49, harvested 10/15/49. (4): E. M. Lindsey, sandy organic; planted 5/19/50, harvested 10 19/50. (5): Chet Main, organic; planted 5/27/50, harvested 9/3/50. (6): R. M. Smith, organic; planted 5/24/50, harvested 10 16/50. (7): Marvin Thomas, organic; planted 5/19/51, harvested 9/17/51. Table 10. Total Yields in Hundredweights Per Acre of Russet Burbank Potatoes from 6 Fertilizer Tests Conducted at the Tulelake Field Station, Siskiyou County Nutrients applied Year of test (pounds per acre) 1947 1948 1949 1950 1951 1952 Av. N P2O5 K2O Yields in hundredweigh is per acre 120 212 387 160 388 359 306 302 60 120 237 418 224 444 332 296 325 120 120 267 432 207 457 366 326 343 120 259 420 164 424 336 310 319 120 60 274 406 196 405 368 293 324 120 120 120 258 414 210 455 386 320 340 60 120 0* 227 417 147 440 352 283 311 L.S.D.5%level 34 N.S. 42 47 N.S. N.S. 21 * Nitrogen derived from sodium nitrate in this treatment. [18] were always darker green in color and slightly larger than those lacking nitro- gen. Plants lacking phosphorus were somewhat more purple in color than those supplied with this nutrient, but there was little or no difference in the amount of foliage. Two tests in addition to those shown in tables 9 and 10 were conducted with Russet Burbank potatoes in 1941. The one test located on fine sandy silt loam soils of fairly high organic content showed an increase in yield with 65 pounds of nitrogen per acre. Higher rates of nitrogen and added phosphoric acid or potash gave no further increases. The second test, on a soil of mineral and peaty muck mixture of rather high organic content, showed a response to 90 pounds of phosphoric acid per acre. OUNTY Two experiments* using the Netted Gem variety were conducted near the town of Standish on a Standish sandy loam soil. In a test in 1941, applying 65 pounds of nitrogen per acre increased the yield from 166 to 254 sacks per acre; * Conducted in cooperation with T. S. Brown, Farm Advisor, Agricultural Extension Service, and Virgil McClure, grower, Standish, Cali- fornia. and in a test in 1944, applying 100 pounds of nitrogen increased the yield from 224 to 268 sacks per acre. In both tests the addition of phosphoric acid gave increases in yield. In the 1941 tests the increase in yield due to phosphoric acid was from 255 to 285 sacks per acre, and in 1944 the increase was from 268 to 292 sacks. The application of potash had no effect on yield. NOMA COUNTY In the spring of 1948 two experiments with White Rose potatoes were conducted in Sonoma County.* One of these was on a very sandy soil one mile south- west of Bodega Bay, and the other was on a sandy loam soil one mile south- * Conducted in cooperation with Don Albini, grower, Valley Ford, California. east of Valley Ford. On the Bodega Bay experiment the plant growth was several times greater in the plots treated with 120 pounds of phosphoric acid per acre, and the yield was increased from 95 to 151 sacks per acre. The yield from 60 pounds of phosphoric acid was midway between none and those receiving 120 19 pounds per acre. In the Valley Ford test, phosphoric acid increased the yield from 104 to only 117 sacks per acre. Plants fertilized with phosphoric acid were also much larger. In both tests the potatoes were grown without irrigation, and it seems certain that with irriga- tion or higher rainfall both nitrogen and liberal amounts of phosphoric acid would be required. Tissue analysis of plants in these tests showed the non-phosphate- treated plants to be the lowest in phos- phorus content of any that have been analyzed in the state. BARA COUNTY An experiment was conducted in Cuyama Valley* in 1943 on a Pinoche fine sandy loam soil. Nitrogen applica- tions caused increases in yield, but phos- phorus and potash application had no effect. The yield from plots lacking nitro- gen was 131 sacks per acre, as compared to 159 and 179 sacks for plots receiving * Conducted in cooperation with E. Smyth, Farm Advisor, Agricultural Extension Service, and J. E. Bell and Adolf Kirschermann, grow- ers, Cuyama, California. 50 and 100 pounds of nitrogen per acre, respectively. In the same year in another experi- ment on a San Emigdio loamy fine sand, plant growth was markedly increased by both nitrogen and phosphoric acid ap- plication. Yield results were not ob- tained. Plants growing on plots lacking nitrogen or phosphorus fertilizer like- wise tested very low in these nutrients, suggesting that yield responses would have been obtained by the use of both nitrogen and phosphorus fertilization. And these are the other results as they are related to potato fertilization Sources of nitrogen and the yields of potatoes On the sandy, heavily irrigated soils the source of nitrogen has proved to be equally as important as the rate of appli- cation. Except for 1943, source-of-nitro- gen experiments were conducted at the U. S. Cotton Field Station at Shafter. The materials were applied by precision ap- plicators and the experiments conducted as for the rate-of-nitrogen tests. The same rates and sources of materials were not used in all the tests; however, in each test comparisons were made with unfer- tilized plots and those receiving compara- ble rates of nitrogen from ammonium sulfate. Other than nitrogen no fertilizer materials were applied, except for the tests in 1952 and 1953 when all plots re- ceived 120 pounds of phosphoric acid per acre. The phosphoric acid was sup- plied from treble super phosphate. There was little difference in the responses dur- ing the various years whether or not phosphorus was applied. The data for these experiments are presented in table 11. Calcium nitrate was compared with ammonium sulfate in two tests, while sodium nitrate was used as a source of nitrate nitrogen in nine tests. Applying [20] (A 3 | CO i-l o • O • CO • iH 1 CM 0? CO ^ • ^ . 1 0) CS CO o • H . Oi • CO • •> O CO • c£> co O 00 co m t~ i-l o CM "tf "tf CO * 2 "^ CO CD l> ^ CD • •^ tH M O CM CO CO (N CM tN i— i- ed E * 5 14 W O o o 00 • CO • CD m ^ cS as M Pi i-l CO ^ i-H CO ■ CM CO 22 3 o m a i-H i-H O • CO CO "tf i-H "^ o OS "* CO co oo . ^ CO lO i-H CO m CO i-l CM CM • i-H • OS • CO C • o ■* OS CM • CO . CD ■ OS • t- c • co o u i-H CM • i-H • i-l • iH cs • .t • x w £ = ■># t- O iH lO -^ lO O o • CM 00 Tt< OJ "tf CO CM O iH O "^ • O CM M- . • c • ic CD £* i-l ^ CO CD ■H >H +■ 49 O o EQ 4* to c. t; * t M -t-» 'S i—l to 3 to > CD i— i ■- B & a 1 1 ^ 3 a c '3 O S < PI 1 1 a a < c c h a s S c B c -S3 5 in Q 09 8 c e i o > CO X^ <« \^5 \C i either 100 or 150 pounds of nitrogen from calcium nitrate produced yields sig- nificantly better than unfertilized plots, but considerably below the yield obtained with comparable rates of nitrogen from ammonium sulfate. Sodium nitrate usu- ally increased the yield above that of the unfertilized plots, but much below that obtained with ammonium sulfate. In four tests sodium nitrate was applied at rates of both 100 and 150 pounds of nitrogen per acre, and the yield from the higher rate was no better than from the 100- pound rate, indicating that the poor re- sults were not due to inadequate rates. Ammonium nitrate was used as a source of nitrogen in six tests. The yields were much better than from unfertilized plots, but still below those receiving a comparable amount of nitrogen from am- monium sulfate. It is likely that most of the benefit from ammonium nitrate can be attributed to the ammonium source of nitrogen and not to the nitrate. In some tests organic fertilizers were used as the entire source of nitrogen; in others comparisons were made using half of the nitrogen from organics and half from ammonium sulfate. Urea was tested against ammonium sulfate in eleven tests. In every test the yield from ammonium sulfate was higher than from the urea, the differences sometimes amounting to as much as 100 sacks or more per acre. In two tests the mixture supplying half of the nitrogen from urea and half from ammonium sulfate was used. Yields were practically the same as those obtained with ammonium sulfate alone and appre- ciably better than those where all of the nitrogen was obtained from urea. In a few tests applying urea 2 inches to the sides and 2 inches below the seed piece resulted in some plant injury, as noted by a slightly reduced stand and dwarfing of the plants. Plants grown with urea were always very dark green in color but usually smaller in size than those grown with ammonium sulfate. Dried blood was used as the sole source of nitrogen in two tests and pro- duced yields only slightly below those obtained from ammonium sulfate. Like- wise the mixture supplying half of the nitrogen from blood and half from am- monium sulfate produced yields averag- ing only slightly below those obtained with ammonium sulfate alone. In no test, however, were better yields produced by using a mixture of half organic nitrogen than from ammonium sulfate alone. The amount of nitrogen removed by the crop was also used as a means of de- termining the relative efficiency of some of the nitrogen carriers. At harvest time the tops and roots were removed from a 20-foot section of row in each of four replicates, and total nitrogen was deter- mined on the sample. For the tubers, 20- pound samples were selected after the total weight per plot was determined. Total nitrogen was also determined on this sample. The data in table 12 give the total pounds of nitrogen removed by the entire plant, calculated to an acre basis. An average for three years showed that unfertilized plants contained about 86 pounds of nitrogen per acre, as compared to 145 and 172 pounds for those ferti- lized with 100 and 150 pounds, respec- tively, from ammonium sulfate. By subtracting the amount of nitrogen re- moved by the unfertilized crop from the others it is seen that the ammonium sul- fate plants removed approximately two thirds of the nitrogen that was applied. Plants fertilized with sodium nitrate re- moved less than 10 per cent of the amount applied, while urea-fertilized plants removed about 30 per cent. The exact reasons for the differences in growth and yield due to the sources of nitrogen are not known. In these sandy, heavily irrigated soils there is much leaching of the nitrate forms of nitrogen. Dried blood evidently becomes available too slowly to be most efficiently used by the crop, and urea often causes injury to the plants. Urea could probably be used as a satisfactory source of nitrogen by [22 Table 12. Amount of Nitrogen in Pounds Per Acre Removed by White Rose Potatoes When Fertilized With Three Nitrogen Carriers U. S. Cotton Field Station, Kern County Yield data for these tests are given in Table 1 1 Source of nitrogen Pounds of nitrogen applied per acre Year of test Av. 1947 1948 1949 None Ammonium sulfate 100 150 100 150 100 Pounds of nitrogen removed per acre 77.6 139.3 177.8 82.6 92.1 111.8 72.4 125.4 138.9 88.0 79.3 93.8 107.2 170.5 198.3 114.9 103.6 133.4 85.7 145.1 171.7 95.2 91.7 113.0 Ammonium sulfate Sodium nitrate Sodium nitrate Uramon placing only about one third of it close to the seed at planting, and then sidedress- ing the remaining two thirds farther out from the plant after the crop is up. If nitrate sources of nitrogen are used, growers should apply only a small amount of the nitrogen at planting and then sidedress with the remainder several times during the growing season. Recent studies (Lorenz and Johnson, 1953; and Lorenz, unpublished) show that all of the poor results from nitrate sources on these sandy soils are not due to leaching. Ammonium sulfate causes marked changes in soil reaction, particu- larly in the region of the fertilizer band. In some instances reduction in soil pH from about 7.5 to as low as 4.5 have been noted. This marked change in soil reac- tion results in the release of considerable native soil phosphorus. When calcium nitrate or sodium nitrate is used as a nitrogen source, there is no detectable change in soil reaction and no release of soil phosphorus. Thus adding phospho- rus fertilizer in addition to the nitrogen sources on these soils results in much greater phosphorus response when it is used with nitrate fertilizers than with ammonium sulfate. Field trials with other vegetable crops on these same soils have demonstrated, however, that nitrate sources cannot be used satisfactorily even if phosphorus is added, unless they can be supplied several times during the growing season. In six tests with potatoes grown on the peat soils of the San Joaquin Delta, com- parisons were made between ammonium sulfate and sodium nitrate. In none of these tests was there any large response to nitrogen fertilization; however, it ap- peared that the results from the two sources were the same. Since these soils are subirrigated and not leached, it is probable that all of the common nitrogen sources would produce equal yields. The data in table 10 show a compari- son of sodium nitrate and ammonium sulfate for potatoes grown for 6 years on an organic soil at the Tulelake Field Sta- tion. The yields produced by ammonium sulfate were only slightly higher than those from sodium nitrate, and the dif- ference between the two sources was not statistically significant. Liquid and injected fertilizers as related to yields During the past few years there has been greatly increased usage of liquid fertilizers both for application in the irri- [23] gation water and for soil injection. The materials may be applied at planting or used as supplemental fertilizers, when they are usually applied sometime after plant emergence. The experiments reported here were all conducted on Hesperia fine sandy loam soils located at or near the U. S. Cotton Field Station at Shafter. The responses from various liquid fertilizers applied in the irrigation water at different periods of plant growth or injected into the soil at planting or plant emergence were eval- uated. Yield comparisons were made with plots lacking nitrogen fertilizer and those receiving ammonium sulfate applied in the conventional manner, 2 inches below and 2 inches to each side of the seed piece. In each test there were four or more plots of each fertilizer treatment arranged at random. When the materials were applied in the irrigation water, the water was first forced through the row and the liquid fertilizer was applied slowly to the irrigation water over a pe- riod of about an hour. Irrigation was then continued for a short time. The ma- terial listed as ammonium hydroxide was supplied from 20 per cent by weight aqueous ammonia (also called aqua am- monia). It was applied slowly enough so that the concentration in the irrigation water was less than 100 parts per million of ammonia. Anhydrous ammonia was injected into the soil by commercial ap- plicators, applied about 6 inches to each side of the plant and 2 inches below the seed piece one week after plant emer- gence. The data in table 13 show the yields from several nitrogen materials applied in the irrigation water at plant emer- gence, a little later than one month after planting. Applications were made at the rate of 100 pounds of nitrogen per acre. Comparisons were made between these and ammonium sulfate placed in the bed at planting. In some treatments a portion Table 13. Total Yield in Hundredweights Per Acre from 3 Tests Com- paring Certain Liquid and Dry Nitrogenous Fertilizers. Each Treatment Received 100 Pounds of Nitrogen Per Acre Source of nitrogen Method of application Time of application* Year of test 1949 1951 1952 None cwt 268 468 393 366 372 319 cwt 113 284 239 220 184 183 174 cwt 86 235 216 179 176 181 Ammonium sulfate / 1/3 ammonium sulfate. . ) 2/3 ammonium hydroxide. f 1/2 ammonium sulfate. . . \ 1/2 ammonium hydroxide. Ammonium sulfate Ammonium hydroxide Urea placed in bed placed in bed in water placed in bed in water in water planting planting \ emergence / planting \ emergence f emergence . . emergence. . emergence. . emergence. . in water in water in water . Sodium nitrate L. S.D. 5% level 43 13 55 * In 1949 potatoes planted on February 8 emerged by March 5, and were harvested on June 21. In 1951 potatoes planted on February 6 emerged by March 20, and were harvested on June 14. In 1952 potatoes planted on February 7 emerged by April 2, and were harvested on June 11. [24] of the nitrogen was supplied from am- monium sulfate at planting and the re- mainder from ammonium hydroxide in the irrigation water at plant emergence. No phosphoric acid was applied. In none of the tests did the application of nitro- gen in the irrigation water at plant emergence produce yields as high as those obtained with ammonium sulfate applied at planting. Also the treatments receiving one third or one half of the nitrogen from ammonium sulfate at planting and the remainder from ammo- nium hydroxide in the irrigation water at emergence yielded less than those re- ceiving all of their nitrogen from ammo- nium sulfate at planting. A comparison of the different nitrogen sources applied in the irrigation water at plant emergence shows that in 2 of the 3 years better results were obtained from ammonium sulfate than from ammonium hydroxide, urea, or sodium nitrate. In the third year all of the sources tested produced about equally. In all compari- sons the yields from ammonium hydrox- ide were about equal to those from urea or sodium nitrate. Further studies included the time of application of ammonium hydroxide in the irrigation water (table 14). Highest yields were obtained by applying all of the nitrogen from ammonium sulfate 2 inches to both sides and 2 inches below the seed at planting. When one third of the nitrogen was supplied from ammo- nium sulfate at planting and the re- mainder from ammonium hydroxide in the irrigation water at plant emergence or 3, 6, or 9 weeks later, the yields from the two latter applications were much below those from the earlier applications. When ammonium hydroxide in the irri- gation water was used as the sole source of nitrogen and applied at intervals after plant emergence, the yields decreased progressively as the applications were delayed. In both of the tests there was very little benefit from applications made 6 weeks or later after plant emergence. Table 14. Total Yield in Hundredweights Per Acre of White Rose Potatoes from Tests Comparing the Times of Application of Am- monium Hydroxide with Bed Placement of Ammonium Sulfate U. S. Cotton Field Station, Kern County Pounds of nitrogen per acre from ammonium sulfate placed in bed at planting Pounds of nitrogen per acre from ammonium hydroxide applied in irrigation water at specified times Year of test 1949* 1951 1 cwt 268 468 372 393 337 324 319 310 212 cwt 113 284 239 213 190 184 144 115 100 0. . 33 67 — at emergence 33 67 — 3 weeks after emergence 33 67 — 6 weeks after emergence 67 — 9 weeks after emergence 33 100 — at emergence 0. 100 — 3 weeks after emergence o 100 — 6 weeks after emergence L. S. D. 5% level 43 13 * 1949 — potatoes planted on February 8 emerged by March 5, and were harvested June 21. t 1951 — potatoes planted on February 7 emerged by April 2, and were harvested June 11. [25 In 1952 a similar experiment was conducted. Half of the nitrogen was sup- plied from ammonium sulfate and placed in the bed at planting. The remainder was derived from ammonium hydroxide and applied in the irrigation water at plant emergence or 3 and 6 weeks later. The yields for the ammonium hydroxide applications made at emergence and 3 weeks later were 216 and 217 sacks per acre, respectively, as compared to only 188 sacks for the application made 6 weeks after emergence. These compare with yields of 235 sacks per acre from plots fertilized with ammonium sulfate at planting and 86 sacks from unfertilized plots. Numerous observations and tests have demonstrated the necessity for applying some fertilizer even before the plants emerge. Consequently, in the injection experiments with anhydrous ammonia, part of the nitrogen was applied from ammonium sulfate placed in the bed 2 inches below and 2 inches to each side of the seed piece at planting, and the remainder from anhydrous ammonia was injected 6 inches to each side and slightly below the seed piece one week after plant emergence. The results from two such tests are presented in tables 15 and 16. In the 1952 experiment the potatoes were planted on February 7, the anhy- drous ammonia was applied on April 4, and harvest was on June 11. The results show that following the application of 60 pounds of nitrogen per acre from am- monium sulfate in the bed at planting, the injection of 60 or 90 pounds of nitro- gen per acre from anhydrous ammonia produced yields identical to those ob- tained when all of the nitrogen was sup- plied from ammonium sulfate at planting (table 15). The 1953 experiment (table 16) was much more extensive. The potatoes were planted and the ammonium sulfate fertilizer applied on February 10. The anhydrous ammonia was injected one week after emergence on March 24, and the potatoes were harvested on June 9. Treble superphosphate at a rate supply- ing 120 pounds of phosphoric acid per acre was applied to all plots at the time of planting. Ammonium sulfate was ap- plied at rates of from none to 180 pounds of nitrogen per acre at 30-pound incre- ments. To plots receiving some of the low rates of nitrogen at planting, anhy- drous ammonia was injected in amounts to make the total rates of nitrogen appli- cation equal to 90, 120, 150, and 180 pounds per acre. In every case the yields produced by the injection treatments were practically identical to those receiv- ing comparable rates of nitrogen from ammonium sulfate at planting. The data indicate that as little as 30 pounds of nitrogen can be applied as ammonium sulfate at planting and the remainder of the nitrogen requirement met by anhy- drous ammonia injection. In no case was there any plant injury noted from inject- ing the anhydrous ammonia 6 inches to the side of the seed piece. Effect of nitrogen sprays on yields Two field experiments were conducted using "Nugreen" as the source of nitro- gen. "Nugreen" is a commercial form of urea analyzing about 44 per cent nitro- gen. In an experiment in 1949 "Nugreen" was applied to the foliage at rates of 5 and 10 pounds per 100 gallons of water. The lower dosage was applied one, three, and six times, and the 10-pound dosage one and three times. The potatoes were planted on February 9 and harvested on June 22. Plants were fully emerged on March 28, and the first sprays were ap- plied on April 20, when the plants were about 10 inches tall. At each spraying the plants were fully wetted until water dripped from the leaves. The amount of spray applied was recorded, and plants sprayed six times with 5 pounds of "Nu- green" per 100 gallons received a total of 25.4 pounds of nitrogen per acre. Those sprayed three times at the 10-pound per [26 Table 1 5. Total Yields in Hundredweights Per Acre of White Rose Potatoes Fertilized With Varying Rates and Combinations of Ammonium Sulfate and Anhydrous Ammonia U. S. Cotton Field Station, Kern County, 1952 Pounds of nitrogen per acre from ammonium sulfate at planting Pounds of nitrogen per acre from anhydrous ammonia one week after emergence Total pounds of nitrogen applied per acre Total yield per acre cwt 101 60 60 219 120 120 260 60 60 120 264 60 90 150 263 L. S. D. 5% level 14 100 gallon rate received a total of 23.8 pounds of nitrogen per acre. The plants were grown without soil application of nitrogen. There were four plots of each spray treatment. The yield data for the sprays are pre- sented in table 17. None of the spray treatments gave a significant increase in yield above that of unfertilized plots. Also none of the sprays produced any Table 16. Total Yields in Hundredweights Per Acre of White Rose Potatoes Fertilized With Varying Rates and Combinations of Ammonium Sulfate and Anhydrous Ammonia U. S. Cotton Field Station, Kern County, 1953 Pounds of nitrogen per acre from ammonium sulfate at planting Pounds of nitrogen per acre from anhydrous ammonia one week after emergence Total pounds of nitrogen applied per acre Total yield per acre cwt — 131 30 - 30 249 60 - 60 297 90 - 90 344 120 - 120 380 150 - 150 377 180 - 180 416 60 60 120 384 60 90 150 392 60 120 180 383 30 60 90 366 30 90 120 365 L. S. D. 5% 40 27] visible effect on the foliage, either as in- creased size or as darker color. The soil used for these tests was definitely defi- cient in nitrogen, as the yield of adj acent plots (fertilized in the soil at planting with 100 pounds of nitrogen per acre from ammonium sulfate) was 468 sacks per acre, as compared to a yield of 243 sacks for the unfertilized plots. A similar experiment was conducted in 1950 but using higher rates of "Nu- green." The potatoes were planted on February 6, had fully emerged by March 15, and were harvested on June 14. The first sprays were applied April 14, about 4 weeks after plant emergence. The plots sprayed with 20 pounds of "Nugreen" per 100 gallons of water at weekly inter- vals received a total of approximately 150 pounds of nitrogen per acre. The re- sults of this test presented in table 18 show no significant increase in yield due to the spray treatments. Adjacent plots receiving 100 pounds of nitrogen from ammonium sulfate at planting yielded 320 sacks per acre, as compared to only 183 sacks for the highest-yielding spray treatment. The spray treatments were not without some effect, however, as plants grown on the sprayed plots were darker in color than those not sprayed. Also the nitrate nitrogen content of the petiole tissue of the sprayed plants on April 21 averaged 273 parts per million on a fresh-weight basis, as compared to only 92 parts per million for those not receiv- ing nitrogen spray. Some burning of the foliage always occurred with the 20 pounds per 100 gal- lon concentration of "Nugreen," and the injury usually became more severe as the air temperatures at time of treatment in- creased. Occasionally there was some burning with the 10 pounds per 100 gal- lon concentration, but it was seldom severe. Table 17. Total Yields in Hun- dredweights Per Acre of White Rose Potatoes When Nitrogen Fertilizer Was Applied as Foliage Sprays U. S. Cotton Field Station, Kern County, 1949 Pounds of "Nugreen" per 100 gallons of water Number of applications of spray Total yield per acre cwt None None 248 5 1* 293 5 3f 274 5 6J 267 10 1* 280 10 st 306 L. S. D. 5% N.S. * Applied April 20. t Applied April 20, 28, May 5. t Applied April 20, 28, May 5, 12, 20, 25. Table 18. Total Yields in Hun- dredweights Per Acre of White Rose Potatoes When Nitrogen Fertilizer Was Applied as Foliage Sprays U. S. Cotton Field Station, Kern County, 1950 Pounds of "Nugreen" per 100 gallons of water Number of applications of spray Total yield per acre cwt None None 148 20 2* 166 20 4f 170 20 61 170 20 Weekly § 174 10 Weekly§ 183 L.S.D. 5% level N.S. * April 14, 21. t April 14, 21, 28, May 5. t April 14, 21, 28, May 5, 11, 26. § April 14, 21, 28, May 5, 11, 26, June 3. 28] Table 19. Total Yields in Hundredweights Per Acre of White Rose Potatoes as Related to Depth of Fertilizer Placement U. S. Cotton Field Station, Kern County Tests by years Depth of fertilizer placement* 1950 1951 33^2 inches below seed piece cwt 299 320 311 256 cwt 306 2 inches below seed piece 321 Level with seed piece 336 2 inches above seed piece 320 L. S. D. 5% level 18 N.S. * 650 pounds per acre of 16-20-0 Ammo-phos fertilizer applied as a double band 2 inches to each side of the seed piece at planting. Depth of fertilizer placement and yields The results from two experiments showing the effect of depth of fertilizer placement on yield of potatoes are pre- sented in table 19. All of the fertilizers were applied in bands 2 inches to each side of the seed piece, so that only the depth of placement varied. The soil type was Hesperia fine sandy loam. In the 1950 test, placing the fertilizer 2 inches above the seed piece resulted in a con- siderably lower yield than placing it 2 inches below the seed. Also a slightly lower yield resulted from placing the fer- tilizer SY2 inches below the seed piece, as compared to only 2 inches below. There was no difference in yield between placing the fertilizer 2 inches below the seed and placing it level with the seed piece. In the 1951 test equally good re- sults were obtained from all of the dif- ferent placements. It is probable that fer- tilizer placement is not very critical for the early-crop potatoes grown on heavily irrigated sandy soils. The fertilizer should be placed far enough away from the seed so that burning of the young seedlings does not occur, and should still be in an area of the soil where it will be readily available to the young plant and where it is not likely to leach from the soil. In commercial fields numerous cases have been observed of fertilizer burn on young seedlings, especially when high rates of nitrogen were used. In these in- stances a better practice would be to place all of the phosphorus and perhaps one third of the nitrogen 2 inches to each side and 2 inches below the seed piece at planting, and then to sidedress with the remainder of the nitrogen at plant emer- gence or shortly thereafter. Fertilizers and grades of potatoes The data in table 20 show the effect of various fertilizer treatments on the grade and yield of potatoes grown for 3 years at the U. S. Cotton Field Station at Shafter. In these tests all of the pota- toes from each plot were processed through a commercial packing shed and graded according to U. S. Department of Agriculture standards. Grading was a combination of machine and hand meth- ods, as is customary for all potatoes grown in this area. In the years 1940 and 1941 when the yield from plots not receiving nitrogen was very low, both the yield and the per- 29 flH S3 N ^"3 09 O H CO CO N lO ffl t» ss °1 |H CO tC (O (O lO IQ O k 0) uu O cn « CO O lO IO CO o ^ C5 E w £ CO O O t-I CO CN CO CN & o k CNJ en *^ 01 H 0) *"! -a N O 00 ^ C3 ^ CO CO e9 W E rt< tJ U3 CO H N CO "tf 6 ti a rH CN C» W H t» N CO H X l M W C- C- CO t- C- t- No. 1's to. 1 wa c 3 u &* 4) t> co a "^ o o c w 1* ^ io to « to to CO CN «/> z k 0) P U b ■o 2 •«■ ■g £ ^ h co w ^ ^ t- CO Ik H o H CO CO CO CO CO CO c .2 c rade a mum S CiH C u » . w "c3 » N lO W W 05 tO tO °I I* IO t- t- > t- t- t* o- E 1- o k tH 73 CO O W u CN CN CN CN CN CN C 3 X G 3 o ^ C- OS O tH O iH t- t- £ ^ t» O CM CO OJ H "^ V) H o tH CN CO CO CO CN CO "C ^™ o ? ■g* q o o o o o o o 00 .2 M IO IO IO IO LO K) !> . "5.8 w iH iH r-i tH i-I i-H V o to a q CN CN CN t- C- t- t> IO o £ i-l iH iH iH tH W Jj s§ p SI o o o o o o o CO 2 m o io o o o H H N (N N i-4 centage of U. S. No. l's was increased by applying 50 pounds or more of nitrogen per acre. In 1942 the yield of U. S. No. l's was increased by nitrogen applica- tions, but the percentage of U. S. No. l's of the total was not affected. In none of the tests did the application of phos- phoric acid or potash have any effect on the percentage of U. S. No. l's. In experiments in Tulare and Madera counties 50-pound samples of tubers were taken from all plots at harvest. The sam- ples were graded by hand, since it was thought that this method would be much more accurate than shed or commercial grading for small lots of potatoes. The potatoes from each plot were placed in two quality grades: U. S. No. l's and a combination of U. S. No. 2's plus culls. In addition the tubers of the U. S. No. 1 grade were sized by the use of rings into three sizes, namely: over 2% inches, 1% to 2% inches, and smaller than 1% inches. All tubers in this grade over 1% inches would be classified as meeting the U. S. Department of Agriculture stand- ards for U. S. No. 1 size A. The data for four tests are presented in tables 21 to 24 inclusive. These tests were selected since the plots showed wide ranges in yield due to fertilizer treatments. The effect of fertilizer treatment on tuber size is best determined by com- parisons within the No. 1 grade. The yield of potatoes over 2 1 / 4 inches in diam- eter increased in direct relation with the total yield. Large total yields were associ- ated with large tubers, and small total yields were associated with small tubers, since the number of tubers per plot did not vary appreciably. Often the yield of potatoes in the 1% to 2 1 / 4 inch size as well as those below 1% inches decreased as the total yield increased. Fertilizers may influence grade by in- creasing or decreasing the yield of No. l's, No. 2's, and culls; or they may in- fluence the percentage of tubers of the total within any particular grade. The yield of both U. S. No. l's and U. S. No. 2's plus culls increased as the total yield increased. When the total yield was low the actual yield of U. S. No. l's was low; however, the percentage by weight of U. S. No. 1 tubers 1% inches or more in diameter (Size A) did not vary greatly or consistently with fertilizer treatment. The total yield of U. S. No. 2's and culls as well as the percentage of these of the total yield increased with any fertilizer treatment associated with a marked in- crease in yield. As the tubers become larger they have a tendency to crack, be- come knobby, or sunburn, which places them in the lower grades. Since the total yields were increased greatly by high nitrogen fertilizer, these treatments were associated with a high yield of No. 2 po- tatoes, but this was not associated with a reduction in the yield of U. S. No. l's. The effect of fertilizers on grade of potatoes was also determined from other tests in Madera and Tulare counties and at Tulelake. The results were in agreement with those reported in tables 20 to 24. As a general summary for tests con- ducted throughout the state, the follow- ing points may be listed in regard to the effect of fertilizers on grade: 1 . In tests where the total yields were increased, the yields of U. S. No. l's and U. S. No. 2's were both increased. 2. There was no effect of fertilizers on the percentage of U. S. No. l's (Size A) unless the yields of the unfertilized plots were very low because of small tuber size. The percentage of U. S. No. l's was in- creased when the fertilizer materially in- creased tuber size from below to above the minimum diameter of 1% inches. 3. All of the three nutrients can im- prove yields of U. S. No. l's when used on soils deficient in any one of the nutri- ents. In these tests nitrogen was the nutri- ent most closely associated with grade, since it was the one most frequently as- sociated with increased total yields. 4. Phosphoric acid and potash applied in addition to nitrogen did not affect the grade of potatoes unless they increased [31] Table 21 . Yields and Grade of White Rose Potatoes from a Fertilizer Ex- periment Conducted on the Kiggens Ranch, Tulare County, 1951 Yield per acre Per cent of total Nutrients applied (pounds per acre) Total U. S. No. 1 grade U.S. No. 2 grade and culls U. S. No. 1 w and over u. s. No. 2 Over2M" lVs-2H" Under 1 % " and culls N P 2 5 K2O 50 100 150 150 150 150 150 150 cwt 231 376 404 406 461 435 cwt 148 276 263 257 305 285 cwt 27 18 13 21 20 17 cwt 4 2 3 5 2 1 cwt 52 80 125 123 134 132 per cent 73 78 68 69 71 69 per cent 23 21 31 30 29 30 L. S. D. 5% level. . . 72 64 N.S. N.S. 51 the total yields. Phosphoric acid did not (as often popularly stated) make smoother potatoes. 5. Both yield and percentage of U. S. No. 2's was usually increased by nitro- gen, phosphoric acid, and potash appli- cations when these nutrients were indi- vidually associated with increased total yields. Fertilizers and keeping quality Several tests were conducted where samples of potatoes from various fer- tilizer treatments were placed in storage and shrinkage losses determined. In two tests in Madera County in 1950 approxi- mately 50-pound samples were taken from each fertilizer plot in the field and Table 22. Yields and Grade of White Rose Potatoes from a Fertilizer Ex- periment Conducted on the Lapadula Ranch, Tulare County, 1951 Nutrients applied (pounds per acre) Yield per acre Per cent of total Total U. S. No. 1 grade U.S. No. 2 grade and culls U. S. No. 1 IVs" and over u. s. No. 2 and culls Over 2 M " m^A" Under 1 % " N P2O5 K2O cwt cwt cwt cwt cwt per cent per cent 118 26 54 14 24 68 20 50 279 170 47 6 56 78 20 100 340 213 31 3 93 73 27 150 368 202 29 4 133 63 36 150 150 412 190 33 3 186 54 45 150 150 150 395 218 29 5 143 63 36 L. S. D. 5% level. . . 31 44 N.S. 5 37 [32] Table 23. Yields and Grade of White Rose Potatoes from a Fertilizer Experiment Conducted on the Frank Martin Ranch, Madera County, 1950 Nutrients applied (pounds per acre) Yield per acre Per cent of total Total U. S. No. 1 grade U.S. No. 2 grade and culls U. S. No. 1 w and over U. S. No. 2 and culls Over V/i " 1K-2M" Under 1%" N P2O5 K2O cwt cwt cwt cwt cwt per cent per cent 166 41 53 28 44 57 27 50 223 80 57 14 72 61 32 100 271 137 47 9 78 68 29 150 . . 290 124 29 9 128 53 44 150 150 283 110 47 13 113 55 40 150 150 150 381 156 24 8 193 47 51 L. S. D. 5% level. . . 34 38 14 9 29 the samples placed in cold storage at 40° F., for 10 days in one test and for 13 days in another. This period of time would ap- proximate the normal transit time from this area to the markets farthest east. At the end of the storage period there were no differences in appearance between po- tatoes from any of the fertilized plots. The data presented in table 25 likewise show that there were no differences in weight loss of potatoes due to any of the fertilizer treatments. Different levels of nitrogen and the addition of phosphoric acid and potash in no way influenced the weight loss by the tubers. In tests conducted at Tulelake, samples Table 24. Yields and Grade of White Rose Potatoes from a Fertilizer Experiment Conducted on the Frank Martin Ranch, Madera County, 1950 Nutrients applied (pounds per acre) N P 2 O s K 2 Yield per acre Per cent of total Total U. S. No. 1 grade U.S. No. 2 grade and culls U. S. No. 1 W and over U. S. No. 2 and culls Over 2*4 " l^-2M" Under 1 y % " cwt cwt cwt cwt cwt per cent per cent 171 54 44 20 53 57 31 50 205 84 24 15 82 53 40 100 198 72 37 12 75 56 38 150 196 58 35 16 87 47 44 150 150 195 67 32 17 79 51 41 150 150 150 191 70 30 15 76 52 40 L. S. D. 5% level. . . 19 N.S. N.S. N.S. N.S. [33] of potatoes from widely different fertil- izer treatments were placed in commer- cial potato storages for periods of 5 months or longer (table 26). In each of three tests the loss in weight during the storage period was about 5 per cent and was in no way related to fertilizer treat- ment. The application of nitrogen, phos- phoric acid, and potash did not influence the weight loss of tubers grown on the re- spective plots. In one test the tubers re- mained in storage from September 12, 1951, to May 1, 1952, and showed ap- preciable sprouting when taken out of storage. The loss due to sprouting was about the same, regardless of the fer- tilizer treatment. Tubers fertilized with nitrogen alone had 3.0 per cent sprouts as compared to 2.5 and 2.2 per cent for the two treatments fertilized with nitro- gen plus phosphoric acid and nitrogen plus phosphorus and potash, respectively. Tissue analysis as related to yields The numerous fertilizer experiments offered many opportunities for studying the effect of fertilizers on the soluble- nutrient content of potato leaf petioles and the relationships of the nutrient lev- els to subsequent yields. Such methods of analysis are commonly referred to as tis- sue testing, leaf analysis, plant analysis, etc. These analyses could be of value in determining whether or not to add addi- tional fertilizers to the crop sampled — providing, of course, that accurate diag- nosis could be made early enough in the growth of the plant. The analyses could also be helpful in determining a particu- lar fertilizer practice to use in future years. Since in these studies it was de- sirable to follow both of these objectives at first, samples were taken when the plants were quite small, and several other samples were taken at regular intervals until near harvest. With later tests sam- pling was restricted to the critical pe- riods, as indicated by the earlier work. For the soluble-nutrient analyses, the third or fourth leaf from the top of the plant was selected. Samples were taken from 30 to 40 plants in each of two or more replicates in each fertilizer treat- ment. Fifteen grams of fresh petiole tis- sue was extracted with 60 ml. of 2 per cent acetic acid, using a Waring Blender. The methods of analysis were essentially those described by Carolus (1938) ex- cept that potassium was determined volu- metrically. Data are expressed on the fresh-weight basis. In some cases a por- Table 25. Weight Loss in Per Cent of White Rose Potatoes During a Short Term Storage at 40° F. (Potatoes Taken from 2 Fertilizer Tests Conducted in Madera County, 1950) Nutrients applied (pounds per acre) Test and days in storage Frank Martin test 10 days at 40° F Charles Haire test 13 days at 40° F N P 2 5 150 150 K 2 150 per cent loss 4.4 4.7 4.2 4.5 4.2 4.4 per cent loss 3.0 50 3.0 100 3.0 150 3.3 150 3.8 150 2.7 Differences in weight loss were not statistically significant in either test. [34] Table 26. Weight Loss in Per Cent of Russet Burbank Potatoes During A Long Period of Storage in Common Storage Houses at Tulelake, California. Potatoes Taken from 3 Fertilizer Experiments Conducted in the Tulelake Area During 1951 and 1952 Test and storage period Nutrients applied (pounds per acre) Oct. 2, 1951, to Mar. 26, 1952 Oct. 7, 1952, to Mar. 14, 1953 Sept. 12, 1951, to May 1, 1952 N P 2 6 K 2 120 per cent loss 5.1 5.9 5.2 per cent loss 4.7 4.2 4.5 5.3 per cent loss 120 5.0 120 120 5.0 120 120 120 5.0 Differences in weight loss were not statistically significant in any of the tests. tion of the petiole tissue also was dried, and analyses were made on the dry tissue for total nitrogen, phosphorus, and po- tassium. The relationship of the nutrient levels with subsequent yields was essen- tially the same whether the fresh or dry material was used. Drying the tissue did, however, result in a much higher soluble- phosphorus level than was obtained from the fresh material. Data selected from only several of many tests are presented to illustrate the possible use of petiole-tissue analysis as an aid both in potato fertilization and in diagnosing nutrient deficiencies in pota- toes. The data also show the variations in nutrient levels found in potatoes at various stages of growth when they are supplied with widely different fertilizer applications. The time of sampling is very im- portant in determining the nutrient level of potato plants. This is shown by the data in table 27, which follow the soluble- nitrogen level of plants fertilized with different rates of nitrogen from ammo- nium sulfate, from the time the plants were first large enough to sample until they approached maturity. The first sam- ples taken about 4 weeks after plant emer- gence tested high in nitrate nitrogen in all plants except those from plots not re- ceiving nitrogen. Two weeks later (sam- ples of May 7) plants receiving 100 pounds or more of nitrogen per acre were still high in nitrate, while those not re- ceiving nitrogen were very low, and those receiving 50 pounds were intermediate. As the plants approached maturity the soluble nitrogen dropped to a very low level in all the plants, regardless of the initial amount of nitrogen that had been supplied. In this test the low nitrate lev- els in the control plants at the first and second samplings were associated with low yields. Similar data are presented in table 28 for plants from a fertilizer experiment in 1953. At both sampling dates the nitrate content in the petiole increased as the amount of nitrogen applied to the soil increased. The first sampling shows a rather definite break in the nitrate con- tent between plants fertilized with 90 and with 120 pounds of nitrogen per acre. Likewise the yield was increased but lit- tle as the nitrogen applied was increased above 120 pounds. There was good agree- ment of yield and nitrate content of the petioles with nitrogen applications up to 120 pounds per acre. At the second sam- [35] Table 27. Nitrate Nitrogen Content of Potato Petioles as Related to Rates of Nitrogen Application and Yields. White Rose Potatoes, Planted March 17, 1941, Emerged about April 5, 1941 U. S. Cotton Field Station, Kern County, 1941 Nitrogen applied (pounds per acre) Total yield per acre Parts per million of nitrate nitrogen in leaf petioles expressed on fresh-weight basis 4/25/41 5 7 41 5/23/41 6/5/41 cwt 140 318 330 359 349 ppm 560 1,350 1,198 1,383 1,360 ppm 22 753 1,378 1,450 1,520 ppm 5 4 115 667 929 ppm 3 10 18 10 112 50 100 150 200 L. S. D. 5% level-yields 37 pling the nitrate content of all plants was low and showed little relation to the yields obtained. The soluble phosphorus was approximately four times higher at the first sampling than the second. Plants not receiving phosphorus were several times lower in phosphorus content than those fertilized with phosphorus, and this Table 28. Nitrate Nitrogen and Phosphorus Content of Potato Petioles As Related to Rates of Nitrogen and Phosphorus Fertilizer Applica- tions and Yields. White Rose Potatoes, Planted February 10, 1953, Emerged March 20, 1953 U. S. Cotton Field Station, Kern Count/, 1953 Nutrients applied (pounds per acre) Total yield per acre Parts per million soluble nutrients in petiole tissue expressed on fresh- weight basis when sampled at two dates Nitrate-Nitrogen Phosphorus 4/30/53 5/20/53 4/30/53 5/20/53 N P 2 6 120 cwt 131 249 297 344 380 377 416 340 ppm 1 65 346 650 1,256 1,344 1,505 1,204 ppm 1 1 1 43 92 190 314 315 ppm 110 206 213 246 295 272 302 47 ppm 67 63 51 44 52 50 70 16 30 120 60 120 90 120 120 120 150 120 180 120 120 L. S. D. 5% level— yields 40 [36] difference was associaed with increased yields from phosphorus fertilization. The data in table 29 are from an ex- periment in the San Joaquin Delta area in 1948, where yield responses were ob- tained from nitrogen, phosphorus, and potassium. The samples were taken just 4 weeks after plant emergence, which was probably a little early to show maximum differences. Low yields were associated with nitrogen levels of less than 700 parts per million, phosphorus levels of less than 80 parts per million, and potash content of about 5,000 parts per million or less. The results of yield and soluble-nutri- ent content from these and over 50 other experiments conducted throughout the State have given us information for mak- ing some general statements regarding the critical nutrient levels of potato plants. The summary below is based on analy- ses expressed on a fresh-weight basis of petiole tissue of the third or fourth leaf from the top of the plant, taken 4 to 6 weeks after emergence: Nutrient levels in the deficient range are practically always associated with re- duced yields, while those in the sufficient range are well on the safe side. Usually plants showing analyses near the critical level will give some response to the ap- propriate fertilizer treatment. If the plants are analyzed within 4 to 6 weeks after emergence and found to be deficient in fertilizer, there is usually still time to add supplemental fertilizers and obtain some yield benefit from them. However, it will often be necessary to allow the crop to grow 2 to 3 weeks longer than usual in order to obtain maximum bene- fit from the added fertilizer. Effect of fertilizers on tuber composition The influence of fertilizers on the com- position of tubers was determined in a number of tests. In some only the specific gravity of the tubers was determined, but in others analyses were made of dry mat- ter, nitrogen, phosphorus, potassium, cal- cium, and magnesium. High specific gravity and high dry-matter content are generally considered to be associated with starchy, high quality, mealy pota- toes. Variety and time of sampling are two important factors affecting dry matter and specific gravity of potatoes. Dry- matter content of tubers usually increases from the time of tuber set until they are mature. This is illustrated by some analy- ses of tubers from an experiment at Shafter in 1946, when the samples were taken at 65, 76, 91, 107, 117, and 124 days after planting. The dry matter on these days was 12.4, 12.6, 18.2, 20.8, 23.2, and 24.3 per cent, respectively. In table 30 are presented the results from four experiments in Tulare County, showing the influence of rates of nitrogen and the application of phosphoric acid and potash on potatoes. The figures rep- resent the results of duplicate samples from four plots in each test. Specific gravity was determined by the use of a Nutrient Deficient range Apparent critical level Sufficient range Nitrate nitrogen (N0 3 -N) ppm Less than 700 . . Less than 40 ... . Less than 5,000. ppm 800 50 6,000 ppm Over 1,000 Phosphate phosphorus (P0 4 -P) Potash (K 2 0) Over 80 Over 9,000 [37] commercial potato hydrometer. In none of these tests was the specific gravity of the tubers materially affected by the ferti- lizer treatment. In tuber samples taken from various fertilizer experiments at Shafter there has been a tendency for potatoes receiv- ing low amounts of nitrogen or none to be higher in specific gravity than those fertilized heavily with nitrogen. In some tests the differences have been very pro- nounced, as illustrated in the data from a test in 1942 (table 31). In this test the specific gravity decreased greatly as the nitrogen supply was increased from none up to 150 or more pounds of nitrogen per acre. The difference when calculated on the basis of starch content amounted to over 4 per cent, as potatoes grown without nitrogen contained 17.0 per cent starch, compared to 12.8 per cent for those receiving 150 pounds of nitrogen per acre. The potatoes grown on the plots receiving the high rates of nitrogen were much more immature at harvest than those grown with low applications of nitrogen or none — which probably ac- counts for the tubers being lower in starch content. If the potatoes on the plots receiving the high rates of nitrogen had been allowed to grow longer, they would undoubtedly have been much higher in starch content. The addition of phosphoric acid and potash had little or no effect on the specific gravity when tested along with 200 pounds of nitrogen per acre. The fact that nitrogen additions did not always result in decreased dry matter in the tubers is shown by data from sam- ples selected from two plots of each nitro- gen treatment for the years 1947, 1948, and 1949 (table 32). In these tests the dry-matter content was approximately the same whether the potatoes were fer- tilized with no nitrogen, 100, or 150 pounds per acre. There was even some indication that the nitrogen-fertilized po- tatoes were higher in dry matter than those grown on plots not supplied with nitrogen. In two tests in Madera County in 1950 Table 29. Nitrate Nitrogen, Phosphorus and Potash Content of Potato Petioles as Related to Rates of Fertilizer Applications and Yields. White Rose Potatoes, Planted June 24, 1948, Emerged July 18, 1948, Sampled August 12, 1948 Terminous, San Joaquin County, 1948 Nutrients applied Total yield per acre Parts per million soluble nutrients in petiole tissue expressed on fresh-weight basis (pounds per acre) Nitrate-nitrogen Phosphorus Potash N P 2 O b K 2 cwt ppm ppm ppm 149 676 30 7,820 160 160 194 547 38 8,640 80 160 160 254 1,279 94 8,645 160 160 160 303 1,318 122 8,380 160 160 247 1,430 23 9,080 160 80 160 275 1,457 78 8,455 160 160 220 1,559 140 5,040 160 160 80 275 1,470 134 7,785 L.S.D. 5% level— yields 54 [38] Table 30. The Specific Gravity of White Rose Potatoes Grown With Different Fertilizer Treatments in 4 Tests in Tulare County During 1951 and 1952. Yield Data for These Tests are Presented in Table 4 Specific gravity, year of test, and grower Nutrients applied (pounds per acre) 1951 Kiggens 1951 Lapadula 1952 Kiggens 1952 Lapadula N P>0 5 K2O 1.082 1.084 1.079 1.076 1.077 1.076 1.073 1.079 1.077 1.074 1.075 1.075 1.076 1.079 1.078 1.076 1.077 1.077 1.086 50 1.087 100 1.089 100 1.086 150 150 1.086 150 150 150 1.083 there was a consistent decrease in dry- matter content of the tubers with increas- ing nitrogen supply (table 33). In both of these tests the tubers from unfertilized plots analyzed about 22 per cent dry mat- ter, as compared to less than 20 per cent in one test and 19 in the other for those receiving 150 pounds of nitrogen per acre. In one of these tests the tubers were also analyzed for nitrogen, phosphorus, and potassium. The nitrogen content was increased by about one third, as the ni- trogen fertilization was increased from none to 150 pounds per acre. The tubers from unfertilized plots analyzed .250 per cent nitrogen on the fresh-weight basis, as compared to .317 and .355 for those receiving 100 and 150 pounds of nitrogen per acre, respectively. In the presence of nitrogen, the phosphorus content of the tubers was increased from .032 to .051 Table 31. The Specific Gravity and Calculated Starch Content of White Roses Potatoes Grown With Different Fertilizer Treatments at the U. S. Cotton Field Station, Kern County, 1942. Planted February 27 and Harvested June 18 Nutrients applied (pounds per acre) Specific gravity Starch — per cent of fresh weight* N P 2 6 160 160 160 160 160 160 K2O 150 150 150 150 150 160 1.096 1.089 1.083 1.075 1.076 1.072 1.074 17.0 50 15.6 100 14.4 150 12.8 200 13.0 200 12.2 200 13.0 * Calculated from specific gravity measure by formula Starch = 17,564 + 199.07 (specific gravity — 1.09879). 39 Table 32. The Dry-Matter Content of White Rose Tubers With Three Rates of Nitrogen Applications Derived From 3 Fertilizer Tests Conducted at the U. S. Cotton Field Station, Kern County (Yield Data for These Tests Are Presented in Table 1 .) Nitrogen applied (pounds per acre) Year of test and dry matter 1947 1948 1949 None : per cent 22.35 23.04 22.55 per cent 21.74 23.64 22.22 per cent 18.81 100 150 19.32 19.56 Year 1947. 1948 1949. Planting date Emergence Harvest February 27 April 5 June 24 February 9 March 10 June 29 February 8 March 5 June 21 per cent by the application of 100 pounds per acre of phosphoric acid. The potas- sium content was likewise increased from .385 to .432 by supplying 150 pounds oi potash per acre. In this test the yield had been increased significantly by nitrogen and potash applications but not by phos- phorus. In the tests with potatoes grown on peat soils in the San Joaquin Delta there has been little effect of fertilizer practice on the dry-matter content of the tubers. In general, tubers grown on these soils have averaged lower in dry matter than in any of the other growing areas. Data from two tests are presented in tables 34 and 35. In the McDonald Island South test, the dry-matter content of the tubers was slightly lower in those receiving ni- trogen than in those lacking nitrogen ap- plications. There was an indication that tubers grown on plots not receiving phos- Table 33. Dry Matter and Total Nitrogen, Phosphorus, and Potassium Contents Expressed as Per Cent of Fresh Weight of White Rose Tubers From 2 Fertilizer Tests Conducted in Madera County, 1950 (Yield Data for These Tests Are Presented in Table 5.) Grower and year of test Nutrients applied (pounds per acre) Haire test — 1950 Dry matter Martin test — 1950 Dry matter N P K N P 2 6 K 2 per cent 22.06 21.60 21.17 19.96 20.38 20.95 per cent 21.89 21.65 20.34 18.68 19.04 20.76 per cent .250 .272 .317 .355 .371 .321 per cent .047 .035 .035 .032 .051 .055 per cent 50 100 150 150 150 .385 150 150 150 .432 [40] phoric acid and potash were lower in dry matter than those receiving either of these elements. The nitrogen content of the tubers was increased from 1.39 to 1.62 per cent of the dry weight by applying 160 pounds of nitrogen per acre. Also the phosphorus content was increased from 0.21 to 0.25 per cent by supplying 160 pounds of phosphoric acid per acre. The potassium content of the tubers was increased only very slightly by potash fertilization, even though the yield was increased markedly. In the north test on McDonald Island (table 35) , there was a marked increase in yield from potash fertilization, al- though there was no effect on dry-matter or potassium content of the tubers. Nitro- gen application had no effect on the per cent of dry matter, although it did slightly increase the nitrogen content of the tubers. Phosphoric acid fertilization caused a slight increase in yield and in- creased the phosphorus content of the tubers from 0.22 to 0.27 per cent. Data are available from only one test in the Tulelake area (table 36). In this test the yield was increased by nitrogen fertilization. The dry-matter content of the tubers was reduced from 24.5 per cent in the tubers not receiving nitrogen to 19.3 for those fertilized with 120 pounds of nitrogen per acre. This was associated with an increased nitrogen content of the tubers from 1.24 to 1.86 per cent. Phosphoric acid applications had no effect on yield or dry-matter con- tent, yet the phosphorus content of the tubers was increased from 0.18 to 0.30 per cent. Potash application had no effect on either the dry-matter or potassium contents. Plant growth and nutrient removal Considerable data were collected rela- tive to growth rates and nutrient removal at various stages of growth. On pages 44 and 45 data are presented comparing growth and nutrient removal by two crops of potatoes grown at two different fertilizer levels at Shafter, California. In both of the years the tubers were still enlarging at the time of harvest, which was 119 days after planting in 1945, and 124 days after planting in 1946. These Table 34. Dry Matter and Total Nitrogen, Phosphorus, and Potassium Contents, and Total Yields of White Rose Potatoes From 1 Fertilizer Test Conducted on McDonald Island (South Test), San Joaquin County, 1948. Planted March 30, Emerged April 30, Harvested September 18 Nutrients applied Total yield per acre Dry matter per cent of fresh weight Per cent of dry weight (pounds per acre) N P K N P2O5 K2O cwt per cent per cent per cent per cent 160 160 ... 387 18.5 1.39 .20 2.02 80 160 160 ... 466 18.3 1.50 .24 2.21 160 160 160 ... 492 17.9 1.62 .25 2.13 160 160 ... 456 17.4 1.56 .21 2.20 160 80 160 ... 464 18.5 1.67 .24 2.13 160 160 ... 374 17.3 1.83 .26 2.07 160 160 80 ... 452 18.0 1.79 .25 1.99 L.S.D. 5% level- yields 77 [41] Table 35. Dry Matter and Total Nitrogen, Phosphorus, and Potassium Contents, and Total Yields of White Rose Potatoes From 1 Fertilizer Test Conducted on McDonald Island (North Test), San Joaquin County, 1948. Planted March 22, Emerged April 20, and Harvested August 18 Nutrients applied Total yield per acre Dry matter per cent of fresh weight Per cent of dry weight (pounds per acre) N p K N P2O5 KoO cwt per cent per cent per cent per cent 160 160 ... 404 18.6 1.84 .23 2.02 80 160 160 ... 380 17.9 2.05 .27 1.95 160 160 160 ... 402 19.2 1.97 .27 2.08 160 160 ... 373 18.4 2.08 .22 1.98 160 80 160 ... 407 18.6 2.02 .26 1.93 160 160 ... 293 17.7 2.02 .26 1.99 160 160 80 ... 357 17.5 2.08 .28 1.95 L.S.D. 5% level- yields 43 may be compared with many commercial fields, which are often harvested 110 days or less after planting. The data indicate that yields could be increased by allow- ing the plants to grow for a longer period. The rate of growth will obviously vary from season to season and with different seed lots. Potatoes planted during the main season in the southern San Joaquin Valley usually emerge from the soil about 30 days after planting, and there is no appreciable tuber growth until 60 or 70 Table 36. Dry Matter and Total Nitrogen, Phosphorus, and Potassium Contents, and Total Yields of Russet Burbank Potatoes From a Fertilizer Test Conducted at the Tulelake Field Station, Siskiyou County, 1948 Planted May 14 and Harvested October 17 Nutrients applied (pounds per acre) Total yield per acre Dry matter per cent of fresh weight Per cent of dry weight N P K N P2O5 K2O cwt per cent per cent per cent per cent 120 ... 387 24.5 1.24 .26 2.21 60 120 ... 418 21.2 1.48 .26 2.27 120 120 ... 432 19.3 1.86 .30 2.25 120 ... 420 20.4 1.72 .18 2.29 120 60 ... 406 19.6 1.73 .26 2.32 120 120 120 ... 414 20.4 1.48 .24 2.36 L.S.D. 5% level- yields N.S. [42] days after planting. Practically the entire growth of the tubers occurs from 60 or 70 to 110 days or longer after planting. In many instances tuber yield was found to increase at rates of from 10 to 15 100- pound sacks per acre per day during rapid periods of growth. The over-all average growth rate for a 400-sack crop produced between 60 and 110 days after planting would be eight sacks per day. The rate of nutrient removal is very closely related to the tuber growth. Dur- ing the first 30 days after planting there is practically no nutrient removal. From 30 to 60 days after planting, all of the nutrients move into the tops, but this usually amounts to less than 10 per cent of that eventually removed by the entire plant. After active tuber growth com- mences, the tubers account for most of the nutrient absorption, and by the time of harvest more than two thirds of the total nutrients removed from the soil are found in the tubers. This should not be interpreted as meaning that growers de- lay fertilizing until about 60 days after planting. The time-of-fertilizer-applica- tion studies showed the best results from fertilizers applied at planting and that little benefit results from fertilizers ap- plied more than one month after plant emergence. In the 1945 test, the yield of the un- fertilized potatoes was 131 sacks per acre. The entire plants had absorbed 59 pounds of nitrogen, 17 pounds of phosphoric acid, and 126 pounds of potash per acre. The tubers alone removed 33 pounds of nitrogen, 14 of phosphoric acid, and 79 of potash per acre. Approximately half of the nutrients were absorbed during the last 30 days of growth. In the same test, plants fertilized with 100 pounds of nitro- gen and 125 pounds each of phosphoric acid and potash per acre removed 148 pounds of nitrogen, 34 of phosphoric acid, and 245 of potash. The yield of tubers was 314 sacks per acre; these ac- counted for the removal of 92 pounds of nitrogen, 25 of phosphoric acid, and 162 of potash per acre. This was equal to about two thirds of the nutrients removed by the entire crop. In the 1946 crop, comparisons were made of unfertilized potatoes and those fertilized with 100 pounds of nitrogen per acre. The unfertilized crop, which yielded 165 sacks per acre, removed 64 pounds of nitrogen, 14 of phosphoric acid, and 138 of potash per acre. Plots fertilized with 100 pounds of nitrogen per acre yielded 375 sacks per acre and removed 121 pounds of nitrogen, 25 of phosphoric acid, and 233 of potash. The tubers accounted for slightly over 80 per cent of the nitrogen and potash removed and nearly 90 per cent of the phosphoric acid. [43] UNFERTILIZED | UJ rr 3 2! 70 80 90 100 110 120 250 "" 200 - POTASH (K 2 0) 150 100 Total Plant 50 •f\ r~^\ 1 "^J^Tub«r 1 1 1 100-125-125 | 140 - 120 - 100- Totol Plant NITROGEN X (N) / 80 / / 60 / // 40 / ^^—_j— Tub«r 20 ( 1 ^1 (III 90 100 110 120 DAYS AFTER PLANTING DAYS AFTER PLANTING Fig. 3. Nutrient removal by entire plants and by tubers alone of unfertilized and fertilized potatoes grown at the U. S. Cotton Field Sta- tion in 1945. The fertilized plot received 100 pounds of nitrogen, 125 pounds of phosphoric acid, and 125 pounds of potash. Growth rate is shown in graph at left. 70 80 90 100 110 120 DAYS AFTER PLANTING [44] o < LU CL 00 O z 3 O CL Z LU cr »- Z 140 UNFERTILIZED J 120 - 100 80 ~ NITROGEN (N) 60 - Totol Plont ^ — 40 - ^^\^^"~~ 20 _L_ ^ ^ Tub«r . — X^\ 1 1 1 1 100-0-0 \ 60 70 80 90 100 110 120 25 20 ~ PHOSPHORIC ACID 15 - (P 2 05) Totol Plont 10 5 I —T^l 1 1 Tube' 1 1 60 70 80 90 100 no 120 60 70 80 90 100 110 250 200 POTASH (K 2 0) Total Plont ^^^^"^ 150 - s£ « — Tub«r 100 " 50 1 '\ 1 1 1 1 90 100 110 120 DAYS AFTER PLANTING DAYS AFTER PLANTING £ 400 u X 350 U a. 300 t- 9 O 250 O i 200 a w 150 > 5 100 m *~ 50 J I I I Fig. 4. Nutrient removal by entire plants and by tubers alone of unfertilized potatoes and those receiving 100 pounds of nitrogen per acre. U. S. Cotton Field Station, Kern County, 1946. 60 70 80 90 100 HO 120 DAYS AFTER PLANTING 45 ] LITERATURE CITED Carolus, R. L. 1938. The use of rapid chemical plant nutrient tests in fertilizer deficiency diag- nosis and vegetable crops research. Va. Truck Exp. Sta. Bui. 98:1531-1556. Fairbank, J. P., and P. A. Minges 1942. An accurate fertilizer applicator for field test plots. Amer. Soc. Hort. Sci. Proc. 41 :310-314. Lindsay, M. A., and H. W. Longfellow 1937. Ammonium sulfate tests on Irish potatoes in Kern County. Univ. of Calif. Agr. Ext. Service Mimeo. Lorenz, 0. A., M. P. Zobel, and J. P. Underhill 1952. Potato fertilizer trials. San Joaquin Delta, 1948, 1949, 1950. University of California Truck Crops Mimeo. No. 54. Lorenz, 0. A., and C. M. Johnson 1953. Nitrogen fertilization as related to the availability of phosphorus in certain California soils. Soil Science 75:119—129. Porter, D. R. 1932. Potato production in California. Calif. Agr. Exp. Sta. Ext. Circ. 61. Porter, D. R., and J. B. Schneider 1939. Potato production in California. Calif. Agr. Exp. Sta. Ext. Circ. 61 (rev.). ACKNOWLEDGMENTS The authors acknowledge the splendid cooperation of the many growers who donated land and otherwise assisted in these tests. Mr. James Perdue, Mr. Fred Howard, and Dr. Mas Yamaguchi assisted in much of the chemical work. The following commercial companies furnished fertilizers and otherwise aided in the studies: Shell Chemical Company; John Grant Company; Agriform Com- pany; Nitrogen Division, Allied Chemical and Dye Corporation; Chilean Nitrate Educational Bureau. In order that the information in our publications may be more intelligible it is sometimes necessary to use trade names of products or equipment rather than complicated descriptive or chemical iden- tifications. In so doing it is unavoidable in some cases that similar products which are on the market under other trade names may not be cited. No endorsement of named products is intended nor is criticism implied of similar products which are not mentioned. [46] Co-operative Extension work in Agriculture and Home Economics, College of Agriculture. Uni co-operating. Distributed in furtherance of the Acts of Congress of May 8, and June 30, 1914 7jm-10,'54(4142)AA IN PRODUCING one fourth of this nation's vegetables There's a bumper crop of jobs in a wide variety of rewarding fields — all helping Califor- nia produce one fourth of the vegetable crop of the United States. growing • shipping • developing new varieties • producing seed sup- plies • chemical fertilizers • pest control • processing contacts. These jobs are hard to fill, for they need very special training. These jobs are thoroughly covered by the University of California vegetable crops curric- ulum at Davis. It provides a balanced and thor- ough course covering all aspects of vegetable production and handling in different areas. breeding • handling • storage and transit • crop varieties • insect studies • plant diseases • weed control • vegetable growth. These jobs require special skills that can be developed only through practical experience under able guidance, using the many and varied facilities that the College of Agriculture at Davis can offer. For further Information . . . write to or 140 acres of land for class work and experiment • greenhouses and spe- cial equipment • irrigation facilities • a faculty of national reputation. Department of Vegetable Crops UNIVERSITY OF CALIFORNIA Davis, California see your University of California Farm Advisor for college entrance requirements