UNIVERSITY OF CALIFORN r . • ;■' St' > II. Fertility Experiments with Potatoes in Southern California O. A. LORENZ K. B. TYLER F. H. TAKATORI J. C. BISHOP P. M. NELSON I. Plant and Soil Analyses as Guides in Potato Nutrition K. B. TYLER O. A. LORENZ F. S. FULLMER CALIFORNIA AGRICULTUR EXPERIMENT STATIO m California farmers grow some 110,000 acres of potatoes, repre- senting a farm value of about $100 mil- lion. Potatoes are produced through- out the state from Tulelake in the north to Riverside County in the south. They are grown on a wide variety of soils ranging from the peat and muck soils of the San Joaquin Delta to the sands of Fresno and San Bernardino counties. As a rule, ferti- lization is heavy but application rates vary greatly from one district to the next, and even within the same pro- ducing area. Adequate diagnostic methods are needed to evaluate the effectiveness of these fertilization prac- tices. In answer to these needs, plant and soil analyses have been developed. They have proved effective tools to assess potato fertilization practices and to predict fertilizer requirements. Plant analyses may be used to indi- cate the adequacy of present and past fertilizer practices for a particular field. As a guide for fertilization of the current season they may be limited, especially for such rapidly growing crops as potatoes; but results can be used effectively as a fertilization guide for subsequent crops in the same field. Soil analyses can often be used to determine the phosphorus and potas- sium needs for the next crop where fertilization needs of the crop are un- known and previous plant analyses are lacking. Soil analyses for these two elements are most useful to determine the need for applying either of these nutrients rather than to determine the quantities that should be applied. This bulletin, in its first part (pages 4-15) reports the results of plant and soil analyses carried out in California between 1956 and 1960. The second part of this bulletin (pages 15-24) summarizes the results of fertilizer experiments conducted in potato fields of southern California during this same period. THE AUTHORS: K. B. Tyler is Assistant Olericulturist in the Experiment Station, Riverside. O. A. Lorenz is Professor of Vegetable Crops and Oleri- culturist in the Experiment Station, Riverside. F. S. Fullmer is Agronomist, American Potash Institute, Newport Beach. F. H. Takatori is Assistant Special- ist in the Department of Vegetable Crops, Riverside. J. C. Bishop is Associate Specialist in the Department of Vegetable Crops, Davis. P. M. Nelson is Labora- tory Technician II in the Department of Vegetable Crops, Riverside. AUGUST, 1961 The authors gratefully acknowledge the excellent cooperation and assist- ance in all phases of the field experiments in the various counties given by Farm Advisors of the Agricultural Extension Service: D. C. Purnell Chino area of San Bernardino County D. N. Wright Kern County M. Snyder and H. Hall Santa Maria Valley, Santa Barbara County V. H. Schweers Tulare County O. A. Harvey and N. C. Welch . . .Western Riverside County The authors thank the various growers who assisted in these experiments by making their land and services available for field tests. Mr. Gilbert Crowell, Mr. Keith Grant, Mr. James Stillman, and Mr. Fred Whiting of the Depart- ment of Vegetable Crops, Riverside, assisted in some of the chemical analyses and in harvesting and sampling the potatoes. Financial assistance for these studies was provided by the California Long White Potato Advisory Board, California Spray-Chemical Corporation, Ameri- can Potash Institute, Inc., Collier Carbon and Chemical Corporation, and Western Phosphates, Incorporated. I PLANT AND SOIL ANALYSES AS GUIDES IN POTATO NUTRITION K. B. Tyler • O. A. Lorenz • F. S. Fullmer CONTENTS Previous Results of Fertilizer Experiments and Nutrient Studies 4 Procedure and Methods 5 Field Experiments 5 Plant Analyses 6 Collection of Samples 6 Sample Preparation 6 Methods of Analysis 6 Soil Analyses 6 Sampling 6 Sample Preparation 7 Soil Analytical Methods 7 Plant Nutrient Surveys 7 Results of Plant and Soil Analyses 7 Plant Analyses 7 Nitrogen 8 Phosphorus 9 Potassium 11 Magnesium 13 Soil Analyses 13 Phosphorus 14 Potassium 14 Literature Cited 24 Previous Results of Fertilizer Experiments and Nutrient Studies 1 The practicability of using plant analyses for improving crop fer- tility practices in California has been demonstrated for several crops including alfalfa (Martin et al, 1955; Salle et ah, 1959) 2 , avocados (Embleton et al., 1960), cotton (Mikkelsen, 1955), oranges (Chapman and Brown, 1950), and sugar beets (Ulrich et al., 1959). Soil analyses have been less frequently employed but have been found useful 1 Submitted for publication, January, i960. : ' See "Literature Cited" for (-Rations referred to in the text by author and date. in work with such crops as cotton (Stromberg, 1960) and grain (Martin and Mikkelsen, 1960). Information on fertilization of po- tatoes in California was reported by Porter (1932) and Porter and Schneider (1939). Davis (1949) presented recom- mendations for the fertilization of po- tatoes in many areas of California. Lorenz et al. (1954) summarized the results of potato fertility studies con- ducted in the major potato producing areas prior to 1954. This publication pointed out that growth response to nitrogen fertilization was universal in the mineral soils of California. Phos- phorus response was fairly common, but up to that time potassium response with potatoes had been observed in very few soils. Since 1954, the need for high rates of nitrogen has been in- vestigated, many areas of phosphate response have been further defined, and growth responses to potash appli- cation have been found in many areas of the state (Lorenz et al., 1956 and 1960; Tyler et al, 1958 and 1960). Tentative nutrient levels for nitro- gen, phosphorus and potassium in the petiole tissue of California-grown po- tatoes were presented by Lorenz et al. (1954). The importance of early samp- ling for determination of nitrate and phosphate in the tissue was empha- sized. From leaf-analysis surveys conducted in Kern and Madera counties in 1954, Fullmer (1957) reported that nitrate- nitrogen was deficient in 30 per cent of the petiole samples from Kern and [4] in 55 per cent of those from Madera County. Phosphate-phosphorus was de- ficient in 18 per cent of the Kern samples and in 30 per cent of those from Madera County. Potassium was rated as deficient or low in 15 per cent of the Kern samples and in 78 per cent of the Madera County samples. A high positive correlation was found between the exchangeable potassium content of the soil and the total potassium con- i tent of the petiole tissue. All these surveys and investigations led to a combined effort of University of California research and extension personnel, fertilizer industry repre- sentatives, and numerous individual potato growers to develop the informa- tion presented in this publication. Procedure and Methods FIELD EXPERIMENTS Fields for potato experiments were selected in each of the producing areas with a view of providing a good repre- sentation of potato soils of that district. Many of the locations were chosen as a result of previous nutrient surveys conducted in that particular area. After selecting a tentative site for a field experiment, soil samples were usually taken from the proposed test location to depths of 10 to 12 inches and analyzed in the laboratory and used as an aid in determining the de- gree of soil-nutrient variability in the field. Upon choosing a fairly uniform site, the experimental plots were laid out in four replications for each treat- ment in randomized block design. Each plot consisted of four single-row beds 60 feet long or two single-row beds 100 feet long, with 32 inches be- tween centers of beds. Cultural opera- tions commonly associated with pro- ducing the potato crop were generally performed by the grower except fer- tilization and, in some cases, planting the seed. A tabulation of tests and field surveys according to year and area is shown below: Field Field Year Production Area Experiments Surveys 1956 Santa Maria Valley 6 25 1957 San Bernardino County - 15 1958 Kern and Tulare Counties 8 20 Riverside County .... 2 13 1959 Kern County 6 — Riverside County .... 8 — San Bernardino County 2 1960 Kern County 1 Riverside County .... 4 — San Bernardino County 3 Total 40 73 For purposes of comparison, basic units of fertilizer application were kept the same in most tests; however, treat- ment combinations were modified slightly from one producing area to another as was thought to be appropri- ate. Nitrogen (N) and phosphorus as P 2 5 were applied in increments of 60 pounds, with potassium as K 2 ap- plied in increments of 100 pounds per acre. Fertilization was accomplished at planting by banding the materials 2 inches below and 2 inches to each side of the row of seed. When applied after planting, usually within two days, the materials were sidedressed 2 inches be- low and 4 to 5 inches to each side of the seed row. Yield measurements at harvest were made in the field using a large sled- borne scale for taking tuber weights from each plot. In each case the po- tatoes were harvested by mechanical diggers and picked up by hand. Yield results were subsequently correlated with plant nutrient levels of petiole tissue from plants of each treatment. Grade determinations on a stub sack taken from each plot were made with the use of a portable grading table. Most experiments were made with the White Rose variety, but results 5] indicate comparable responses in yield and plant composition to those ob- tained using Russet Burbank, Pontiac and Kennebec varieties. PLANT ANALYSES Collection of samples Sampling was initiated when the plants were about 12 inches high and continued at approximately two-week intervals throughout the season. Each sample consisted of 40 to 50 petioles of the fourth leaf below the growing tip of the plant. In general, the fourth leaf is the youngest fully expanded leaf of the plant. The petiole samples con- sisted of that portion of the plant be- tween the stem and the base of the first leaflet. For convenience in classifi- cation the samplings were arranged into three categories with respect to age of the plant as follows: Early season From the stage when plants were first large enough to provide ap- propriate samples until blossoming or beginning of tuber set. In general, this was four to eight weeks after plant emergence. Midseason From blossoming or early tuber set until tubers were half-grown. Gen- erally from six to ten weeks after emergence. Late season From time tubers were half-grown until maturity. Since length of growing season for potatoes varies widely, even within the same district, it is advisable to classify plants and samples according to their physiological age rather than to age from planting. Under certain ideal conditions tubers may be harvested within 90 days from planting while under other conditions the crop may be grown for as long as 150 days before harvest. Also, depending on dormancy of the seed and soil temperatures, po- tatoes in one field may emerge in two weeks while under other conditions it may take six weeks or even longer for emergence. The ideal point from which to date potato samples would be emergence, but growers seldom maintain records of the emergence date; for practical purposes, such as the use of these techniques by com- mercial laboratories, the planting date must frequently be used. Sample preparation After collection, petiole samples were thoroughly washed in tap water and rinsed under distilled water to remove soil particles, dusts, sprays and other possible surface contaminants. Drying was accomplished in a forced- draft oven at 70°C. When thoroughly dried, the samples were ground to pass a 40-mesh screen and stored until analyzed. Methods of Analysis Petiole samples were routinely ana- lyzed for total calcium, potassium, and magnesium in the ash and for nitrate- nitrogen and phosphate-phosphorus extractable from the dried, ground samples in 2 per cent acetic acid solu- tion. Methods of analysis and dry ash- ing were similar to those described by Johnson and Ulrich (1959). Calcium and potassium were ana- lyzed with the Perkin-Elmer flame photometer and magnesium by the Thiazole Yellow method (Young and Gill, 1951). Nitrate-nitrogen in the extract was determined by the phenol- disulfonic acid method and phosphate- phosphorus by the ammonium mo- lybdate-stannous chloride procedure. SOIL ANALYSES Sampling In sampling the soil of a prospective field experiment, one composite sam- ple was taken from the area of each replication so that a comparison of the samples from each of the four replica- [6] tions would provide an index of the soil variability within the experiment. Each soil sample consisted of a com- posite of 20 to 30 cores from the surface foot taken with an Oakfield soil tube. Sample preparation Samples brought to the laboratory from the field were first allowed to air- dry by spreading the soil thinly on large pieces of paper and leaving it several days in a room where there was no risk of contamination. When dry, the samples were rolled to break the clods and passed through a 2 mm sieve. Soil analytical methods In analyzing for the exchangeable cations — sodium, calcium, potassium, and magnesium — 50 grams of air-dry soil were extracted with 500 ml of neutral, normal ammonium acetate. Analyses of the extract for the first three elements were effected using a Perkin-Elmer flame photometer. The Thiazole Yellow method (Young and Gill, 1951) was employed for determin- ing magnesium in the same extract. Available phosphorus in the soil was determined by the bicarbonate extrac- tion method described by Olsen et al. (1954) and expressed as P0 4 . Electrical conductivity of the saturation extract and pH measurements of the 1:1 soil to water suspension were also taken on each soil sample. PLANT NUTRIENT SURVEYS In addition to the replicated field experiments, nutrient surveys of 73 growers' fields were conducted. These surveys consisted of taking soil samples from randomly selected fields and of analyzing petioles from plants growing in these fields. In 1958 the survey in- cluded sampling replicated strips in each of 20 fields which had received high rates of phosphorus or potassium in addition to what fertilizer the grower might have supplied. No yield data were obtained from fields in- cluded in the surveys. Many of the field experiment locations in 1958 and 1959 were chosen on the basis of the nutrient surveys of previous years. Results of Plant and Soil Analyses Results of the analyses are based primarily on samples collected from 40 replicated field fertilizer experi- ments and from 73 field nutrient sur- veys conducted with potatoes in Cali- fornia during the years 1955 through 1960. Because it was impractical to present the vast volume of data re- sulting from these studies, examples typical of the conditions described are presented to emphasize the important aspects of the study. PLANT ANALYSES Petiole levels of nitrogen, phos- phorus and potassium varied consider- ably according to age of the potato plant and to nutrient availability. During the early growing season, plant levels of these three nutrients were 12,000- E 9- 9,000 o. z i O 6,000- 3,000 - YIELD OL/A 1 100 Days after Planting Fig. 1. Nitrate-nitrogen concentrations in leaf petioles and tuber yields of White Rose potatoes fertilized with five rates of nitrogen. (Field Experiment 6-59, Riverside County). [7] relatively high, but without fertiliza- tion they decreased rapidly. Since so much variation existed with stage of growth, the time of sampling was of major importance in characterizing the nutrient status of any given field of potatoes. In addition, experience has indicated that sampling should be done on at least two separate dates to ascertain reliably the true nutrient status of a given crop. Nitrogen The data in figure 1 were taken from a field experiment in Riverside County. The trend shown here is fairly typical of that observed in similar ex- periments in other areas. As the potato growing season progressed, nitrate- nitrogen in the plant decreased rapidly. In many fields, nitrate-nitrogen was relatively high in the leaf petioles in early season but decreased rapidly with growth and maturity. Even though nitrogen concentrations may decrease to low levels at late season, yields generally remained unaffected, as in this test, if sufficient nitrogen was maintained through midseason growth. High levels of nitrate-nitrogen found in plants approaching maturity meant that sufficient or excess nitrogen was applied to the crop. This does not mean that these levels of nitrogen were required for the production of maxi- mum yields. Nitrate-nitrogen fre- quently drops to practically zero in mature plants without yield reduc- tions, and larger differences in nitrate levels are obtained in early season with varying rates of nitrogen applied. For these reasons, early and mid-season samplings are more reliable than late- season samplings for reflecting the nitrogen status of the potato crop. Early samplings not only are more accurate in predicting likely yield re- sponse to nitrogen fertilization, they also often allow time for diagnosing plant needs and for applying ad- I5,000r 12,000- i o 9,000 •£ 6,000 o Q. 3,000 Early 60 70 80 Midseason 90 Late Days after Planting Fig. 2. Nitrate-nitrogen concentrations in leaf petioles and tuber yields of White Rose potatoes fertilized with six rates of nitrogen. (Field Experiment 1-60, San Bernardino County). ditional nitrogen fertilizer for use by the current crop. In contrast to figure 1, figure 2 shows levels of petiole nitrate-nitrogen in plants grown on a soil better sup- plied with available nitrogen. Yields leveled off above the 120 pound rate of nitrogen and high petiole concen- trations of nitrate were maintained in plants receiving 180 pounds or more of nitrogen per acre. At the two lower rates of nitrogen application, the ni- trate levels in the plant decreased rapidly from midseason. The wide range of nitrate-nitrogen concentrations found in potato plants during growth is shown in figure 3. The upper curve of this graph indi- cates the highest levels of nitrate ob- served in plants from a field very high in nitrogen while the lower curve marks the lowest levels found in plants from a test which did not receive nitro- [8] 25,000 20,000 15,000 k> 2E a: 10.000 5,000 N0 3 -N Early Midseason Late Fig. 3. Range of nitrate-nitrogen levels ana- lyzed in leaf petioles of potatoes. Levels below shaded portion considered deficient. 5,000 „400 YIELD E CL °- 4,000 or 1 3,000 <300 •200 * 100 O |[ 1 O. 60 120 ^ Lbs. P 2 5 /Acre 2,000 CL ^0 20 "^^^60\. 1,000 ■v/ •— 50 Early 60 70 Midseason 80 90 Late Days after Planting Fig. 4. Phosphate-phosphorus concentra- tions in leaf petioles and tuber yields of White Rose potatoes fertilized with three rates of phosphorus. (Field experiment 11-59, River- side County). gen fertilizer. Analyses which fall above the shaded sector would be con- sidered sufficient in nitrate content and would, as far as this nutrient is concerned, produce high tuber yields. Analyses falling in the shaded area may or may not result in maximum yields, depending on the particular growth conditions of the potato plants. Values below the shaded portion would be classified as deficient and normally would be associated with re- duced yields. Based on the results of these field in- vestigations, the following ranges are recommended as a guide in determin- ing the nitrogen status of a potato crop through petiole analysis: ppm Nitrate-nitrogen (NO ;j -N) in petiole — DRY WEIGHT BASIS Defi- Inter- Age of Plant cient mediate Sufficient Early season <8,000 8,000-12,000 > 12,000 Midseason ...< 6,000 6,000-9,000 > 9,000 Late season . . <3,000 3,000-5,000 >5,000 Phosphorus Phosphorus in the potato plant generally decreases in concentration with age and maturity, but less rapidly than nitrogen. Changes in phosphorus concentration of potato plants from a soil of low phosphate availability (26 ppm P0 4 ), with and without applied phosphorus, are shown in figure 4. In this field the supply of available phos- phorus was very low and yields were unsatisfactory unless phosphorus was added to the soil. At early-season sampling the phosphorus levels in plants taken from the three differently treated plots varied markedly from one treatment to another; however, at the final sampling in late season, plants from all three treatments were low and similar in phosphorus content. This point emphasizes the necessity of early sampling — in early or mid- season — to evaluate accurately the phosphorus status of potatoes. [9 5,000 4,000 3.000 2,000 1,000 No yield response to P application OLa, 50 60 70 80 90 Eorly Midseason Late Days after Planting Fig. 5. Phosphate-phosphorus concentra- tions in leaf petioles of Kennebec potatoes fertilized with three rates of phosphorus. (Field experiment 5-60, Riverside County). The data in figure 5 show levels of petiole phosphorus in plants grown on a soil somewhat better supplied with available phosphorus (69 ppm P0 4 ), and where no yield response was obtained by phosphorus fertilization. In this field, phosphorus levels re- mained fairly high throughout the season in both the untreated and the fertilized plants although phosphorus application did maintain plant phos- phorus at a higher level throughout the sampling period. Plant analyses are especially useful in detecting phosphorus deficiency in potatoes. Plants growing in fields with- out sufficient phosphorus often remain undetected because symptoms of phos- phorus deficiency consist merely of stunted or retarded plant growth. Without normal plants in the same field for comparison, phosphorus de- ficiency by visual observation defies proper diagnosis. 12,000 10,000 ^\^^ 8,000 . po 4 -p 6,000 4,000 2,000 ■ c^^^ Early Midseason Late Fig. 6. Range of phosphate-phosphorus levels analyzed in leaf petioles of potatoes. Levels below shaded portion considered de- ficient. ^ E 3 "w W o £ YIELD 70 Days 80 90 100 after Planting 120 Fig. 7. Petiole potassium levels and tuber yields of White Rose potatoes fertilized with four rates of potassium. (Field experiment 6- 58, Kern County). [10 As shown in figure 6, extremely high and very low levels of phosphorus have been found in petioles of California potatoes. Upper and lower curves of the graph mark the limits of the wide range of phosphate-phosphorus petiole concentrations found in plants grow- ing in different potato fields. Phos- phorus values falling below the shaded portion indicate deficiency levels which normally result in reduced tuber yields. Analyses falling above the shaded area indicate levels of suf- ficiency where no response to phos- phorus fertilization would be expected. Values falling in the shaded portion may or may not indicate deficiency, depending on the particular growing conditions. By relating plant phosphorus analy- ses to yield results, the following classi- fication is suggested to indicate the phosphorus concentration ranges in the potato plant: PPM PHOSPHATF.-PHOSPHORUS (P0 4 P) IN PETIOLE DRY WEIGHT BASIS Defi- Inter- Age of Plant cient mediate Sufficient Early season < 1,200 1,200-2,000 > 2,000 Midseason ..< 800 800-1,600 > 1,600 Late season .. < 500 500-1,000 > 1,000 Potassium During early growth, potassium con- centrations are fairly high in young potato plants regardless of the avail- ability of the nutrient in the soil. How- ever, as the season progresses, differ- ences in potassium concentration re- lated to its soil availability become greater. This is seen in figure 7 which shows results from a potato experiment on a soil of low exchangeable potas- sium (46 ppm K). At early season, plants from all treatments of this test were within a narrow range of potas- sium concentrations. At midseason the difference between the unfertilized plants and those which received 400 pounds of K was more than several No yield response to K application ^^ Early Midseason 60 70 80 90 100 120 Days after Planting Fig. 8. Petiole potassium levels of White Rose potatoes fertilized with two rates of potassium. (Field 23-58, Kern County). fold the difference at early season and this difference remained large the rest of the season. The data in figure 8 show potassium levels in plants grown on a soil well supplied with available potassium. Potassium levels were high throughout the season in both potas- sium-fertilized and nonpotassium-fer- tilized plants. With potassium fertiliza- tion the early season concentration of this nutrient was 14.5 per cent as con- trasted to 12 per cent in the nonpotas- sium-fertilized plants. At late season comparable values for the potassium- fertilized and nonpotassium-fertilized plants were 9 per cent and 8 per cent, respectively. From the information presented in figure 7, the necessity for later samp- ling to determine reliably the potas- sium status of potato plants can be understood. Before midseason, potas- sium levels, as contrasted with nitro- gen and phosphorus levels, are not well defined, and very early prediction through plant analyses of response to [in potassium fertilization is seldom reli- able. Differences in potassium content between potassium-deficient plants and those grown with sufficient potassium fertilizer remain small until tuber growth commences. Usually these dif- ferences become greater as the plants approach maturity. Potassium concentrations in the plant can be maintained relatively high throughout the growing season, even in potassium-deficient soils (figure 7), provided that sufficient potassium is applied to the soil. Even though yields have been increased by potas- sium fertilization in numerous areas of California, with few exceptions the magnitude of these increased yields has not been nearly as large as those obtained with nitrogen and phos- phorus fertilization. Plant potassium may often drop to very low levels during the late growing season with- out greatly reducing potato yields. Through use of a systematic program of plant petiole analyses and by care- ful observation for leaf symptoms, po- tassium deficiencies can be diagnosed and remedial action taken to prevent / ,:< >* Potassium deficiency symptoms in potato leaves. 16 r 14 12 10 ui 8 o Early Midseason Late Fig. 9. Range of petiole potassium levels analyzed in potatoes. Levels below shaded por- tion considered deficient. serious yield losses of subsequent crops. Foliar symptoms of potassium de- ficiency were observed in all fields where yield response to potassium ap plication was obtained. These symp- toms were characterized by leaf scorch and bronzing and spotting of the leaves as shown in the photo on the left. Small necrotic areas on the stems and at the nodes were also common. In some areas the symptoms were simi- lar but in addition, leaf roll of the younger leaves preceded the appear- ance of the other symptoms and the entire foliage took on a darker, blue- green cast which set it apart from plants adequately supplied with po- tassium. Such symptoms were observed in a number of Kern County fields where tuber yields remained unaf- fected by potassium applications. That these plants were on the borderline of potassium deficiency was further veri- fied by petiole analyses which showed them to be low in potassium (4 to 6 per cent K) at the end of the season. Visual symptoms of potassium defi- [12 ciency usually are not noted until the later stages of plant growth. As shown in figure 9, potassium levels in petioles of potato plants were found as high as 16 per cent at mid- season and as low as 0.2 per cent at late season. The deficiency levels for potassium through the various stages of growth are indicated by the portion of the graph beneath the shaded area, Analyses above the shaded area indi- cate potassium sufficiency and those found within the shaded sector may or may not be deficient. A classification compiled on the basis of these experiments is pre- sented below to aid in assessing the potassium status of the potato crop: Per cent potassium (K) in petiole — DRY WEIGHT BASIS Deft- Inter- Age of Plant cient mediate Sufficient Early season <9 9-11 >11 Midseason <7 7-9 >9 Late season <4 4-6 > 6 Magnesium Magnesium levels in potato petioles were found from 0.25 per cent to 2.5 per cent as indicated by the two curves in figure 10 which show the upper and lower limits of magnesium Lbs. K 2 per acre 3- Mg Early Midseason Late Fig. 10. Range of petiole magnesium con- centrations analyzed in potatoes. o Days after Planting Fig. 11. Petiole magnesium levels in White Rose potatoes fertilized with four rates of potassium. (Field experiment 7-58, Kern County). concentrations analyzed in California potatoes. Magnesium concentrations generally increased with the age of the plant and at final sampling were often double or triple the concentration found at the earliest sampling. Magnesium concentration in the plant invariably was decreased by po- tassium fertilization, as shown in fig- ure 11. In certain instances where this occurred, magnesium appeared to be approaching the deficiency levels of less than 0.20 per cent proposed by other investigators, although symp- toms generally attributed to magne- sium deficiency have not yet been di- agnosed in California potatoes. SOIL ANALYSES Reliable soil tests are useful prior to the production of a crop in an area where cropping history is lacking or where proper fertilizer practices have not been determined. Soil tests are of additional value in determining whether abnormal plant behavior is [13 due to a nutrient deficiency or to a climatic, pathological, soil or other conditions. To be of maximum use and reli- ability in fertility investigations, soil tests must be correlated with nutrient levels in the crop plant and to yield response. Each plant species varies in its ability to remove nutrients from the soil, and nutrient levels which may be more than adequate for plants such as small grains may be deficient for other crops such as potatoes or celery. Phosphorus Soil levels of bicarbonate soluble phosphate (P0 4 ) as low as 14 ppm and as high as 160 ppm were ana- lyzed in the potato soils of California. Soil phosphate values as related to plant phosphorus concentrations at midseason, and tuber yields are shown in figure 12. Fields in which soil phos- phate was less than 40 ppm responded by increased yields when fertilized with phosphorus. In these same fields 160 140 120 100 - 80 60 40 20- Response to P -No response 500 1000 1500 Plant P0.-P 2000 2500 p.p.m. Fig. 12. Relation of phosphate-phosphorus in potato leaf petioles at midseason to bicar- bonate soluble phosphorus in the soil. From 1958-59 field experiments. plant phosphorus levels were gen- erally deficient at midseason — less than 800 ppm — where phosphorus ap- plication was omitted. In the range be- tween 40 and 80 ppm soil phosphate, there were some fields which gave a yield response to phosphorus applica- tion but many did not; in this soil phosphorus range, plant phosphorus concentrations were divided between the deficiency range and the inter- mediate range. Above 80 ppm soil phosphate, yield responses were lack- ing and plant levels of phosphorus were high. From the results of these experi- ments and surveys the following classi- fication of soil phosphorus levels is suggested: Parts per million bicarbonate soluble phosphate (p0 4 ) in soil air drv basis <40 ppm-Deficient Response to phosphorus fertilization 40-80 ppm-Intermediate Response to phosphorus fertilization unlikely >80 ppm-Sufficient No response to phosphorus fertilization Potassium Exchangeable soil potassium (K) values varied widely in California potato soils ranging from 30 to 400 ppm. Most of the low-potassium soils were of lighter texture and had been in potato production for a number of years. Many of the soils which have been cropped frequently to potatoes, heavy feeders on potassium, show signs of becoming depleted of the ex- changeable form of this nutrient. Sam- ples from strips of uncropped soil bordering on older potato fields ana- lyzed up to four times higher in ex- changeable potassium than those from corresponding adjacent areas within the potato fields. Plotting exchangeable soil potas- sium values against plant petiole po- tassium at. late season makes it pos- sible to distinguish soil levels which [14 • 400 350 . E d. a-300 . •• • • 2£ = 250 - • • • Exchangeable o o o o " • • • • •• • • •• •• • •• -> • 4 1 • Deficient Medium! Sufficient I 2 3 4 5 6 7 8 9 10 II 12 13 Plant K, % Fig. 13. Relation of potassium in potato leaf petioles at late season to exchangeable potassium in the soil. From 1956-59 field surveys and experiments. may be considered as deficient and sufficient for producing maximum po- tato yields (figure 13). In soils where the exchangeable potassium level was less than 100 ppm, plant potassium was generally in the deficient range — less than 4 per cent at late-season sampling. Between 100 and 150 ppm the points are scattered, indicating yield response to potassium applica- tion to be uncertain. Above 150 ppm soil potassium the response is un- likely and above 200 ppm a yield re- sponse in potatoes to potassium fer- tilization is highly improbable. This information is summarized as follows: Parts per million exchangeable poi \ssii \i (k) in soil air drv basis < 100 ppm-Deficient Response to potassium fertilization 100-150 ppm-Lou- May respond to potassium fertilization 150-200 ppm-Medium Response to potassium fertilization unlikely >200 ppm-Sufficient No response to potassium fertilization 11 FERTILITY EXPERIMENTS WITH POTATOES IN SOUTHERN CALIFORNIA O.A. Lorenz • K.B.Tyler • F. H.Takatori J. C. Bishop • P. M. Nelson CONTENTS Santa Maria Valley 17 Western Riverside County 17 Chino Area — San Bernardino County 19 Kern and Tulare Counties 21 Literature Cited 24 The results of numerous potato fertilizer experiments conducted in many areas of California pre- vious to 1954 were reported by Lorenz et al. (1954). Since that time, much new and additional information has been obtained, particularly from areas in southern California. The data from each experiment in the various areas have been reported in detail in several mimeographed reports (Lorenz et al.. 1956 and 1960; Tyler et al., 1958 and 1960). The second part of this bul- letin summarizes the results by areas for fertilizer experiments conducted [15 from 1956 through 1960. Data of soil analyses from the various experiments are also included. Nitrogen in the form of ammonium sulfate was applied at rates from to 300 pounds per acre at 60-pound in- crements. Phosphorus was applied at rates of 0, 60, and 120 pounds of P 2 5 per acre from treble superphosphate. In most tests, potassium from sulfate of potash was applied at rates of 0, 100 and 200 pounds K 2 per acre but in some tests applications as high as 1,000 pounds per acre were made. Nitrogen levels were tested in the presence of 120 pounds of P 2 O g per acre and or 200 pounds of K 2 per acre. Phosphorus levels were tested in combination with rates of 180 or 240 pounds of nitrogen per acre and with or 200 pounds of K 2 per acre. Po- tassium levels were tested in combina- tion with nitrogen applied at 180 or 240 pounds per acre and with phos- phorus at 120 pounds P 2 5 per acre. The fertilizer materials were banded approximately 2 inches to each side and 2 inches below the seed piece at planting, or were banded slightly farther from the seed piece within a day or two after planting. In each field there were four plots per fer- tilizer treatment. Each plot consisted of four rows 60 feet long or two rows 100 feet long. Petiole samples from plants in plots TABLE 1. FERTILIZER TREATMENTS AND TOTAL YIELDS OF POTATOES FROM SIX FERTILIZER EXPERIMENTS IN SANTA MARIA VALLEY— 1956. BUSSET BUKBANK VARIETY Total yields— cwt. per acre Fertilizer treatment (lbs/acre) Fields Ave. 1-56 2-56 3-56 4-56 5-56 6-56 Nitrogen (N) 214 314 266 305 331 266 149 266 339 361 331 58 270 398 461 517 483 461 403 461 467 475 494 43 253 310 337 356 343 337 289 337 341 368 365 33 356 387 360 367 379 360 356 360 367 364 376 N.S. 265 297 281 296 270 281 282 281 284 310 313 N.S. 248 334 366 362 366 366 327 366 371 357 356 38 273 60. . . 340 120 345 180 367 Phosphorus (P2O5) 362 100 345 Potassium (K2O) 301 100 345 200 .. . 362 400 .. . 373 600 .. . 373 L.S.D. 5% level Soil Data Soil type pH Parts per million in soil Field Exchangeable K Bicarbonate soluble P0 4 1-56 7.3 6.5 7.4 7.9 6.7 100 50 175 100 100 136 2-56 3-56 Yolo fine sandy loam 174 4-56 Yolo silt loam 175 5-56 Yolo fine sandy loam 175 6-56 Yolo fine sandy loam 195 [16 of all fertilizer experiments were col- lected and analyzed at intervals of ap- proximately two weeks during the growing season. Data from these were used to help establish the plant nu- trient concentrations presented in the first part of this bulletin. Santa Maria Valley The experiments in Santa Maria Valley were conducted with the Netted Gem variety in 1956. Results of these tests are presented in table 1. The yields showed marked responses from nitrogen and potassium applica- tions but not from phosphorus. A complete interpretation of the nitro- gen effect is not possible since some nitrogen from aqua ammonia was ap- plied in the irrigation water to four of the fields, and yields from plots with- out nitrogen were not available. Field 1 received 12 pounds of nitrogen per acre, Field 2 had 48 pounds, Field 4 received 40 pounds, and Field 6 re- ceived 36 pounds. In four of the six fields, nitrogen application in excess of that in the irrigation water gave a significant increase in yield and in the two other fields the same trends were observed. In at least three of the fields, higher yields were obtained from ap- plications of 120 or 180 pounds of nitrogen than from only 60. Based on these observations, applications of from 120 to 180 pounds of nitrogen per acre should result in good produc- tion, with the higher rate required on the more sandy and heavily leached soils. There was no yield increase from phosphorus application in any of the six tests. Petiole analyses showed that the plants had a high concentration of this nutrient. It is probable that the phosphorus level of many of these soils had been built up by past ap- plications since analyses show that the soil phosphorus levels were very high. Potassium fertilizers produced sig- nificant increases in yield in four of the six tests. In the Pleasanton sandy loam soil, considerably higher yields were obtained from application of 200 pounds per acre or more of potash than from only 100 pounds. In this test, plants which received less than 200 pounds of potash per acre ex- hibited marked symptoms of potas- sium deficiency. The two fields which did not give significant increases from potassium had received heavy applica- tions of manure during the past years. The exchangeable soil potassium level of one of these was at a level con- sidered to be sufficient and the other in a range where yield response has not usually been obtained. Western Riverside County Thirteen fertilizer experiments were conducted in western Riverside County from 1958 to 1960, inclusive. In all experiments, nitrogen was ap- plied at rates as high as 240 pounds per acre. Excellent yield increases due to nitrogen were obtained in every ex- periment. In five of the 13 experi- ments, higher yields were obtained with 240 pounds of nitrogen per acre than with lesser amounts. On the other hand, in three experiments there was little or no increase in yield from applications greater than 60 pounds of nitrogen per acre. In these three soils the organic matter had been increased appreciably by the addition of much plant residue. In another three tests there were yield increases with nitro- gen additions of 120 pounds per acre with no additional benefit from in- creased rates. These data are presented in table 2. The averages for the 13 fields show that 60 and 120 pounds of nitrogen per acre increased the yields 78 and 1 12 sacks per acre, respectively, as compared to the untreated plots. The application of 180 and 240 [17] cpcG CO o to CO CO 00 O) ■* lO N °p U q z o u H2 2 co n s o id t— "* t~- CO O <— i "f Oi Oi <— i co -f t 1 -"-r co co x to » * to O) OS CT> CO i-i CM CO CO — i CM CO CO CO -h CO CO CO CO CO •f to lO CO *N O0 00 W O -H CO — OS CO Tf ■* -*f CO — < f N -i tO tO CN - CM O OS O CO OtOO N * OO O! ® i-h CO OJ Oi O) H OS CM CM CM CM CO CM ass I £ r§s«°§§ £J -i o CM Tt< >> 83 > O 2 White Rose Russet Burbank White Rose White Rose White Rose White Rose White Rose Russet Burbank White Rose Kennebec White Rose White Rose White Rose 'o CO a a o 1 a a *9 «1 OOOlOOOOOtO-P"— i ffl ffi 00 00 3 o oO'ffos'O'— i *— i »ra i-- r-- <— i <— i w a > -1-2 *o oq Hanford sandy loam Hanford sandy loam Ramona sandy loam Hanford sandy loam Ramona sandy loam Ramona sandy loam Ramona sandy loam Hanford sandy loam Ramona sandy loam Hanford sandy loam Ramona sandy loam Riverwash sand Riverwash loamy sar 2 OOOOCTiOSOSOSO^O^OOOOO 0)OO00OO«W1 | 10®NX pounds of nitrogen per acre in each case increased the yield by only eight sacks per acre over the next lowest rate of application. The effect of phosphorus fertiliza- tion was tested in 12 experiments. In four of the 12, phosphorus application had little or no effect on yield. In four other experiments, yield increases re- sulted from fertilization with 60 pounds of P.,0- per acre, however higher rates of application failed to provide any additional yield increases. In the remaining four tests, 120 pounds of P.,0- per acre produced yield increases above those obtained at the 60 pound rate. Averages of all the tests showed that 60 pounds of P 2 O g per acre resulted in a yield in- crease of 32 sacks of potatoes and that applying 120 pounds per acre in- creased the yield 17 sacks above that obtained with only 60 pounds. Twelve of the 13 experiments showed no definite yield response to potassium fertilization and in one field only was there any conclusive evi- dence of response to this nutrient. In this latter case, the yield was increased, the composition of potassium within the plant greatly increased, and po- tassium deficiency symptoms of the plant eliminated or reduced by potas- sium application. Exchangeable soil potassium was at levels considered to be sufficient for potatoes in all except four fields. Of these four, three were at levels where yield increases might or might not be expected with potassium fertilization. The other was at a level considered to be deficient and in this soil a yield increase was obtained by potassium fertilization. Chino Area — San Bernardino County Five fertilizer experiments were con- ducted in the Chino area during 1959 and 1960. The results of these are [19] TABLE 3. FERTILIZER TREATMENTS AND TOTAL YIELDS OF POTATOES FROM FIVE FERTILIZER EXPERIMENTS IN THE CHINO AREA OF SAN BERNARDINO COUNTY. 1959-60. WHITE ROSE VARIETY * Significant response to P2O5 at 5% level. t No significant response to K2O. Soil Data Total yields — cwt. per acre Fertilizer treatment (lbs/acre) Fields Average five fields 1-60 2-60 3-60 7-59 12-59 Nitrogen (N) 120 263 284 307 307 329 297 307 307 310 174 344 356 373 374 374 286 374 374 398 116 248 284 278 353 354 318 353 353 366 145 359 401 423 440 439 440 440 440 420 224 347 379 404 422 415 382 422 422 424 156 60 312 120 . 341 180 357 240 379 300 382 Phosphorus (P2O6) 120 Potassium (K2O) 345 379* 379 200 384 1 Field 1-60 2-60 3-60 7-59 12-59 Soil type Hanford sandy loam Hanf ord fine sand . . . Tujunga fine sand. . . Hanford fine sand . . . Hanford fine sand . . . pH 7.4 7.2 7.6 7.1 8.1 Parts per million in soil Exchangeable K 94 63 94 172 Bicarbonate soluble PO4 172 53 given in table 3. Increased yield re- sponses to nitrogen fertilization were obtained in all tests. In all of the ex- periments, yields were increased by nitrogen applications up to 180 pounds per acre. In three experiments there were definite trends for highest yields with applications of 240 pounds of nitrogen per acre with little or no additional benefit by increasing the rate to 300 pounds per acre. An aver- age for the five experiments shows that 60 pounds of nitrogen per acre increased the yield by 156 sacks, or double that of the unfertilized plots. The application of 120 pounds per acre increased the yield by only 29 sacks above that obtained with the 60-pound rate. Additional yield in- creases resulting from nitrogen appli- cation at rates of 180, 240 and 300 pounds per acre were 16, 22 and 3 sacks per acre, respectively. Yield increases of 35 sacks per acre or more due to phosphorus applica- tions were obtained in three of the five tests. An average of the five tests shows that 120 pounds P 2 5 per acre re- sulted in a yield increase of 34 sacks per acre as compared to the non- phosphorus fertilized plots. The soil analyses show that phosphorus was low in four of the fields and relatively high in one. In this latter field there was no increase in yield due to phos- phorus fertilization. Based on an average of all the tests, potassium application failed to in- [20 crease tuber yields significantly. In one field (2-60) where exchangeable soil potassium was extremely low, foliar symptoms of potassium deficiency were evident and plant potassium was deficient throughout the season. In this field and in three others where soil potassium was on the borderline of deficiency and where plant potas- sium levels were low, potassium ferti- lization resulted in large increases — from 30 to 80 per cent higher concen- trations — in petiole potassium levels. In the fifth field (7-59) where the soil was well supplied with exchangeable potassium, application of potassium resulted in a very small increase in plant uptake of this nutrient. Kern and Tulare Counties Thirteen fertilizer experiments were conducted with White Rose potatoes in Kern and Tulare counties in 1958 and 1959. In nine of the experiments comparisons were made of rates of application of nitrogen, phosphorus, and potassium, but in the remaining four experiments only rates of appli- cation of phosphorus were compared. Results of the nine experiments are presented in table 4. Yields during the 1958 season were somewhat below the average for this area due to unfavor- able growing conditions. Plant re- sponses to nitrogen were observed in all experiments. Applications of nitro- gen greater than 60 pounds per acre resulted in a significant increase in yield in seven of the nine experiments and in the remaining two similar trends were observed. An average for the nine experi- ments shows that 120 pounds of nitro- gen per acre increased yields 49 sacks above that obtained with the 60- pound rate. Additional yield increases obtained from nitrogen fertilization at rates of 180 and 240 pounds per acre were 19 and 12 sacks, respectively. In only one experiment of these nine was there a significant yield in- crease due to phosphorus fertilization. An average of these experiments in- dicates that almost identical yields were obtained on plots fertilized with 120 pounds of phosphoric acid and those not receiving phosphorus. Soil analyses showed phosphorus to be within the medium range in three fields and high or sufficient in the re- mainder. In the four additional phosphorus fertilizer experiments conducted in 1959 (table 5) only one failed to ex- hibit a yield response to phosphorus application. In two of the experi- ments, yields were increased by phos- phorus applications of 100 pounds P.,0- per acre with no additional benefit from increased amounts. In the remaining experiment the highest yields were obtained with 400 pounds P 9 0. per acre. An average of the four tests reveals that 100 pounds of P.O. per acre increased the yield by 31 sacks per acre. In three of these fields avail- able soil phosphorus was low or de- ficient and of a medium concentra- tion in the fourth, where no yield in- crease due |o the application of this nutrient was observed. In four of the nine experiments (table 4) there were significant yield increases with the application of 100 pounds of K 2 0. In the remaining fields similar trends were observed although the yield differences were not large enough to be statistically significant. An average of the nine fields shows that 100 pounds of K.O increased yields by 31 sacks per acre, however yields were not increased with higher rates of potassium. In all of the nine experiments, potassium content of the plants was greatly in- creased and potassium deficiency symptoms eliminated or reduced by potassium fertilization. Soil analyses show that exchangeable potassium was low or below 100 ppm in three of the 21] soils and only slightly above this level in the other samples. The data presented in figure 14 summarize the yield response to rates of nitrogen application in the four areas. The yields between the various areas are not strictly comparable since the tests in the areas were conducted during different seasons, some of which were much more favorable for potato production than others. The Kern and Tulare county tests were conducted in 1958 when the yields were low as compared to other years. The data serve best as illustrating the rates of nitrogen associated with 50 100 150 200 250 300 POUNDS OF NITROGEN APPLIED PER ACRE Fig. 14. Rates of nitrogen application from ammonium sulfate and yield of potatoes for southern California producing areas. TABLE 4. FERTILIZER TREATMENTS AND TOTAL YIELDS OF POTATOES FROM NINE FERTILIZER EXPERIMENTS. KERN AND TULARE COUNTIES. 1958-59. WHITE ROSE VARIETY Fertilizer treatment (lbs/acre) Nitrogen (N) 60 120 180 240 Phosphorus (P2O5) 120 Potassium (K2O) 100 200 400 1000 L.S.D. 5% level.. Total yields — cwt. per acre Fields 1-58 185 225 230 227 226 230 211 212 230 214 2-58 3-58 4-58 5-58 6-58 7-58 8-58 162 157 171 116 183 203 308 166 189 210 194 243 269 365 175 217 206 224 266 304 391 190 211 223 249 283 312 404 188 178 244 215 275 327 391 175 217 206 224 266 304 391 156 195 194 174 194 296 386 161 229 218 230 258 341 408 175 217 206 224 266 304 391 176 193 222 221 254 313 406 171 211 232 210 298 310 379 34 14 30 42 42 43 48 5-59 482 548 571 576 571 536 563 571 577 Average of all fields 219 268 287 299 291 287 260 291 287 286 Soil Data Soil type pH Parts per million in soil Field Exchangeable K Bicarbonate soluble PO4 1-58 Delano sandy loam 6.0 4.6 4.6 4.7 6.9 7.0 7.1 7.4 7.0 101 106 104 105 70 46 101 93 80 142 159 80 157 101 80 HI 41 49 2-58 Delano sandy loam 3-58 Hanford sandy loam 4-58 Delano sandy loam 5-58 Hesperia sandy loam 6-58 Hesperia sandy loam 7-58 Hesperia sandy loam 8-58 Hesperia sandy loam 5-59 Hesperia sandy loam 22 ] TABLE 5. POTATO TUBER YIELDS FROM FOUR PHOSPHORUS FERTILIZER EXPERIMENTS. KERN COUNTY. 1959. WHITE ROSE VARIETY Rate of phosphorus (lbs P20f, per acre) Total yields — cwt. per acre Fields Average of all fields 1-59 2-59 3-59 4-59 455 435 430 482 477 476 527 529 538 407 447 457 492 442 100 473 200 400 Soil Data Soil type pH Parts per million in soil Field Exchangeable K Bicarbonate soluble P0 4 1-59 6.9 5 5 8.7 8.1 93 136 223 333 60 2-59 29 3-59 33 4-59 30 the maximum yield within the areas. The curves were fitted using the quad- ratic equation y = a + bx + ex 2 , where x = pound increments of nitrogen, and y = yield in hundredweights per acre. The equations for predicting yields as related to rate of nitrogen ap- plication are as follows: Santa Maria Valley y = 248.75 + .8552x - .00097x 2 Chino area y = 177.70+ 1.820x-.00394x 2 Western Riverside County y = 229.80 + 1 .327x - .00386x 2 Kern and Tulare counties y= 125.26+ 1.1825x-.00257x 2 In the Santa Maria Valley tests the calculated yields were still increasing at the highest rate of nitrogen applied which was 240 pounds per acre. With experiments in the Chino area of San Bernardino County maximum yields were obtained with 230 pounds ol nitrogen per acre and the yields ob- tained from applications between 200 and 270 pounds of nitrogen were nearly identical. In the Riverside County experiments 200 pounds ol nitrogen produced the highest yields. Small differences in yields were ob- tained with applications of between 180 and 240 pounds of nitrogen per acre. The Kern and Tulare county ex- periments showed that maximum yields were obtained with about 230 pounds of nitrogen per acre with little yield increase from nitrogen applica- tions greater than 180 pounds per acre. 23 LITERATURE CITED Chapman, H. D., and S. M. Brown. 1950. Analysis of orange leaves for diagnosing nutrient status with reference to potassium. Hilgardia. 19:501-540. Davis, G. N. 1949. Growing potatoes in California. Calif. Agr. Ext. Service Cir. 154. Embleton, T. W., W. W. Jones, and M. J. Garber. 1960. Fertilization of the avocado. Calif. Agr. 14 (1): 12. Fullmer, F. S. 1957. Leaf and soil analysis survey in two California potato growing areas. Amer. Soc. Hon. Sci. Proc. 70:385-390. Johnson, C. M., and A. Ulrich. 1959. Analytical methods for use in plant analysis. Calif. Agr. Exp. Sta. Bui. 766:25-78. Lorenz, O. A., J. C. Bishop, B. J. Hoyle, M. P. Zobel, P. A. Minges, L. D. Doneen, and A. Ulrich. 1954. Potato fertilizer experiments in California. Calif. Agr. Exp. Sta. Bui. 744:1-46. ■, F. H. Takatori, Herman Timm, J. W. Oswald, Tulley Bowman, F. S. Fullmer, Marvin Snyder, and Harwood Hall. 1956. Potato fertilizer and blackspot studies, Santa Maria Valley — 1956. Vegetable Crops Series No. 88. -, K. B. Tyler, F. H. Takatori, P. M. Nelson, and D. C. Purnell. 1960. Potato fertility studies in Chino area of San Bernardino County 1957-60. Vegetable Crops Series No. 107. Martin, W. E., A. Ulrich, M. D. Morse, and D. S. Mikkelsen. 1955. Potassium deficiency of alfalfa in California. Better Crops with Plant Food. 39 (1 0):6— 12. , and D. S. Mikkelsen. 1960. Grain fertilization in California. Calif. Agr. Exp. Sta. Ext. Service Bui. 775:1-40. Mikkelsen, D. S. 1955. Cotton phosphate fertilization. Calif. Agr. 9 (1):7, 15. Olsen, S. R., C. V. Cole, F. S. Watanabe, and L. A. Dean. 1954. Estimation of available phosphorus in soils by extraction with sodium bicarbonate, U.S.D.A. Cir. 939. Porter, D. R. 1932. Potato production in California. Calif. Agr. Exp. Sta. Ext. Cir. 61. , and J. B. Schneider. 1939. Potato production in California. Calif. Agr. Exp. Sta. Ext. Cir. 61 (rev.). Sallee, W. R., A Ulrich, W. E. Martin, and B. A. Krantz. 1959. High phosphorus for alfalfa. Calif. Agr. 13 (8):7, 8. Strom berg, L. K. 1960. Need for potassium fertilizer on cotton determined by leaf and soil analyses. Calif. Agr 14(4):4-5. Tyler, K. B., O. A. Lorenz, P. M. Nelson, J. C. Bishop, Herman Timm, F. S. Fullmer, V. H. Schweers, and D. N. Wright. 1958. Potato fertilizer studies Kern and Tulare Counties Spring 1960. Vegetable Crops Series No. 94. , O. A. Lorenz, F. H. Takatori, P. M. Nelson, O. A. Harvey, and N. C. Welch. 1960. Potato fertility studies in western Riversid-e County 1957-60. Vegetable Crops Series No. 108. Ulrich, A., F. J. Hills, D. Ririe, A. G. George, and M. D. Morse. 1959. Plant analysis, a guide for sugar beet fertilization. Calif. Agr. Exp. Sta. Bui. 766:1-23. Young, H. V., and R. Z. Gill. 1951. Determination of magnesium in plant tissue with thiazole yellow. Anal. Chem. 23:751. 7!m-8,'63 (C440).7.F.