**•"«/ Division of Agricultural Sciences UNIVERSITY OF CALIFORNIA *<^ SWEET CORN FERTILITY EXPFRII IN THE COACHELLA VALLEY « I K. B. TYLER A. F. VAN MAREN O. A. LORENZ F. H. TAKATORI CALIFORNIA AGRICULTURAL EXPERIMENT STATI O N BULLETIN 808 SWEET CORN FERTILITY Experiments in the Coachella Valley THIS BULLETIN summarizes the results for nine crops of sweet corn grown with various rates of commercial fertilizer and ani- mal manures. It reports the effects of the treatments on yield, plant composition, and soil composition. THIS BULLETIN will help sweet corn growers determine their fertilizer needs, particularly on crops grown under light sandy soil conditions. THE AUTHORS: K. B. Tyler is Assistant Olericulturist in the Experiment Station, River- side; A. F. Van Maren is Farm Advisor in the Extension Service, River- side; O. A. Lorenz is Olericulturist in the Experiment Station, Davis; and F. H. Takatori is Associate Specialist in the Experiment Station, Riverside. DECEMBER, 1964 2] THE FINDINGS Field experiments were conducted in the Coachella Valley of California to evalu- ate fertilizer effects of manure, to study changes in soil chemical composition re- sulting from repeated manuring and fer- tilizing with N and P, and to determine nutrient deficiency levels in sweet corn and relate these to yield and time of sampling. Most of the results came from a long-term study in which sweet corn was grown for nine consecutive spring and fall crops. Soil and growing condi- tions were representative of sweet corn production in the Coachella Valley. Ammonium sulfate, as a nitrogen source, was much more efficient than feedlot manure in producing high yields in sweet corn. One hundred pounds of N from ammonium sulfate produced yields comparable to 500 lbs of N from manure (10-ton rate). Indications were that the manure was more efficient in supplying P and K than in its ability to supply N to the growing crop. Manuring and inorganic N fertiliza- tion both increased salinity of surface soil, although manuring had a more in- jurious effect on stand and growth of the corn plants. Manure applications mark- edly increased bicarbonate soluble P and exchangeable K, Mg, and Na in the soil. Exchangeable Ca and soil pH were changed very little by manure additions. Appreciable movement of nutrients to the lower soil depth (12- to 24-inch) occurred in the manured soils but not in the non- manured soils. Results developed by these experi- ments demonstrate that plant tissue anal- ysis can be used effectively for diagnos- ing the status of N and P available for sweet corn production. Midrib tissue of leaves opposite the primary ear was used for plant analysis. Levels of NO s -N and P0 4 -P extractable with 2 per cent acetic acid below 500 ppm were considered deficient. Above 1,000 ppm, either nu- trient would be considered sufficient at the early tassel stage of growth. Sweet corn, an important vegetable crop in California, is grown on more than 20,000 acres a year, having a farm value of nearly 7 million dollars (Calif. Crop and Livestock Rep. Serv., 1963). While the crop is grown throughout the state, more than 70 per cent of the total acre- age is found in the five southern Cali- fornia counties of Kern, Los Angeles, Orange, Riverside, and San Bernardino. More than 5,000 acres are grown in the Coachella Valley of Riverside County where the experiments described in this bulletin were conducted. Fertilization of sweet corn generally includes the use of nitrogen. Application rates vary markedly and depend on the supply of available nitrogen in the soil as influenced by the texture and porosity of soils on which the corn is grown, as well as on the season of growth. Rates of nitrogen as low as 50 pounds per acre are often used for plantings on fine-tex- tured soils, yet four to six times that rate is commonly used on corn grown on sandy soils such as those found in the Chino area of western San Bernardino County or in the Coachella Valley. One- fourth to half of the nitrogen may be applied at planting and the remainder in two or more post planting applica- tions. The use of phosphorus for sweet corn has been increasing. The application of animal manures — dairy, feedlot, and poultry — is a common practice for supplying nutrients to sweet corn in most areas of southern California. Large supplies of manure, available at fairly low costs, make the use of these materials attractive, especially to vegeta- ble growers. The usual practice for sweet corn has been to broadcast the manure prior to the preparation of the seed bed. Application rates vary from 3 to about 10 tons of manure per acre. A number of field fertility experiments with sweet corn have been conducted in southern California. Generally, these ex- periments have shown responses to ni- [3] trogen and manures, but little or no re- sponse to phosphorus and potassium. Shadbolt (1959) investigated the influ- ence of plant spacing and nitrogen fer- tilization on shriveling kernels of sweet corn. He concluded that the rate of ni- trogen was less important in preventing shrivel than the timing of nitrogen ap- plication. Late nitrogen application re- duced the occurrence and severity of shrivel. MacGillivray et al. (1962) stated that a high level of nitrogen is required by sweet corn during the early growth and that nitrogen can be supplied either by chemical fertilizers or by manures. They recommended 10 to 12 tons of barnyard manure per acre, or 4 to 5 tons poultry manure applied and worked into the soil before planting. They also stated that phosphorus fertilization may prove bene- ficial for early plantings in certain areas, including some parts of Coachella Valley. The experiments described here were conducted with the following objectives: 1) to evaluate the effectiveness of cur- rent fertility practices, especially with reference to manuring for sweet corn production; 2) to determine nutrient de- ficiency levels in sweet corn which might help assess the nutrient status of any given crop of sweet corn; 3) to evaluate the changes in soil chemical composi- tion, pH, and salinity from repeated fer- tilizing with chemical fertilizers and manure. METHODS A long-term field study was established in the Oasis District in Coachella Valley in the spring of 1959. This study included nine consecutive crops; five in the spring and four in the fall. The variety of sweet corn was Golden Cross Bantam, T Strain. Spring corn plantings were made from January 14 to 24. Fall corn plantings varied from August 23 to September 6. Individual plots were 12 feet wide and 60 feet long. The rows were 3 feet apart and plants were thinned to about 8 inches in the row. Plots were replicated four times for each treatment and were arranged in randomized block design. Plots received the same treatment throughout the nine consecutive tests. The fertilizer treatments consisted of three rates of inorganic N, three rates of manure, two combinations of manure and inorganic N, and two rates of inorganic P. In addition, there were two manure treatments which were imposed on spring corn but omitted in the fall season to test the residual effect from the spring crop to the fall crop. Fertilizer materials applied broadcast prior to planting included all of the in- organic P, half of the inorganic N and all of the manure. These materials were in- corporated into the surface soil with a spring-tooth harrow. Following this the soil was harrowed, furrowed-out and then irrigated. When sufficiently dry, the soil was disked, bedded up, and planted. When corn plants were 12 to 15 inches high the remaining N was ap- plied by sidedressing 6 to 8 inches on each side of the plant row and about 3 inches deep. In the fall season the post- plant N was applied in two equal appli- cations instead of only one; the first, two to three weeks after emergence; and the second, when plants were about 18 inches high. Inorganic N was in the form of ammonium sulfate (21 per cent N) and inorganic P was applied as treble super- phosphate (20 per cent P). Each crop re- ceived a different lot of steer manure ob- tained from near-by feedlots. Analyses of all lots of manure were similar and averaged 16 per cent moisture, 2.5 per cent N, 0.6 per cent P, 3.2 per cent K, 1.6 per cent Ca, 0.8 per cent Mg and 1.6 per cent Na. The soil was Coachella very fine sand, [4] a Red Desert Aeolian Sand, calcareous in both surface and subsoil. The soil was very low in organic matter, less than 0.5 per cent, and had a cation exchange ca- pacity of 5.02 meq per 100 grams. Both the soil and the cultural methods were typical for much of the sweet corn grown in the Coachella Valley. Soil samples of the surface layer of soil (0 to 12 inches deep) were collected at the start of the experiment and periodically during the study. Available soil phosphate (P0 4 ) was determined by the bicarbonate extraction method of Olsen et at. (1954) and is ex- pressed as parts per million P. Exchange- able potassium, calcium, magnesium, and sodium were extracted using neutral, nor- mal ammonium acetate as the extractant and are expressed as parts per million K, Ca, Mg, and Na, respectively. Soil pH and electrical conductivity of the satura- tion extract were determined on all soil samples. Plant sampling was initiated when the first ears appeared on plants growing in the most advanced plots. Sampling was continued at two-week intervals and two to three samplings were obtained from each plot for every crop. Sections of midribs of leaves opposite and above the primary ear were collected, washed, dried, ground, and analyzed. Nitrate (N0 3 ) and phosphate (P0 4 ) in midrib tissue were extracted with 2 per cent acetic acid and analyzed according to methods described by Johnson and Ul- rich (1959). These values were reported as parts per million N and P, respec- tively. Total potassium (K), calcium (Ca), and magnesium (Mg) were determined after ashing a sample of the midrib tissue. Sweet corn yields were determined after picking and grading all ears from 100 feet of the two center rows of each plot. Usually two harvests were made and the yields were expressed as dozens of marketable ears per acre. Table 1. AVERAGE SEASONAL YIELDS AND DAYS FROM PLANTING OF SWEET CORN TO 50 PER CENT SILKING AS INFLUENCED BY FERTILIZER APPLICATION Treatment Fertilizer treatment Average marketable yields* Average time from plant- ing to 50 per cent silking comparisons N P Manure Spring Fall Spring Fall lbs/acre tons/acre doz/acre days 52 107 a 232 a Rates of N 100 52 931 b 774 b 97 58 200 52 1171c 880 b 97 57 400 52 1175 c 847 b 99 58 Rates of P 400 911a 726 a 102 58 400 52 1175 b 847 a 99 58 52 107 a 232 a Rates of manure 52 5 703 b 726 b 94 56 52 10 980 c 860 b 93 56 52 20 953 c 859 b 93 56 Rates of N + 5 tons 52 5 703 a 726 a 94 56 manure 200 52 5 1150 b 993 a 94 56 400 52 5 1106 b 814 a 96 57 ♦ Residual effect of 52 107 a 232 a manure 52 5t 582 b 656 b 96 58 52 lot 881c 690 b 94 57 * Values in each comparison followed by the same letter are not significantly different at the 5 per cent level t Manure applied in these treatments to spring crop but omitted for fall crop. [5] RESULTS Yields The influence of inorganic N alone, manure alone, and combinations of in- organic N and manure on sweet corn yields are shown in figure 1 and table 1. Yields of all inorganic N fertilized corn were higher in the five spring crops than in the four fall crops. This was also true for plots receiving 10 and 20 tons of manure per acre. Where inorganic N alone was applied for spring-fall crops (graph la), the largest increase in yield resulted from the first 100-lb increment and there was no increase from applica- tions greater than 200 lbs N per acre. Ten tons of manure alone produced much higher yields of spring corn than 5 tons alone. Yields from the 20-ton applications were little different than those from 10 tons (graph lb). In the fall corn, there were indications that 200 lbs N with 5 tons manure was better than any rate of N alone or any rate of manure alone. In the spring crops, N alone at 200 or 400 lbs per acre was as good or better than the 200 lbs N, 5-ton manure treatment. Inorganic phosphorus application at the rate of 52 lbs P per acre increased yields 22 per cent in spring as compared to corn receiving neither P nor manure (see table 1). Spring corn fertilized with 200 lbs N and 52 lbs P per acre yielded no higher when 5 tons of manure per acre were applied. The 5- and 10-ton manure applica- tions applied only to the spring crop were compared with applications made twice yearly. Yields of fall corn from plots manured both in the spring and fall were superior to those manured only for the spring crop. Five and 10 tons of manure applied twice yearly produced fall yields of 726 and 860 dozen per acre, respectively. This increase at the 10- ton rate was about 25 per cent in favor of the twice-yearly manuring of sweet corn. There was considerable carry-over effect of the spring manure fertilization to the fall crop, when com- pared with the unfertilized corn (table 1). Unfertilized corn yields in fall were 232 dozen per acre as contrasted with 656 and 690 dozen per acre from plots re- ceiving only spring applications of 5 and 10 tons of manure per acre, respectively. Effects of inorganic N and manure fertilization on average weight of ears are shown in figure 2. The first increment SPRING - 5 crops 800 400 200 100 200 RATE OF N Lbs /Acre N a MANURE 5 10 20 RATE OF MANURE Tons /Acre 100 200 400 RATE OF N+5T. MANURE Lbs /Acre Fig. 1. Sweet corn yields as influenced by a) nitrogen, b) manure, and c) combinations of nitrogen with manure. [6] 400 5 10 RATE OF MANURE Lbs /Acre Tons /Acre Fig. 2. The effect of nitrogen and manure fertilization on ear weight of sweet corn. 100 200 RATE OF N of inorganic N (100-lb rate) produced the largest increase in ear weight of spring corn. Ear size continued to in- crease with N applications up to 200 lbs or more of N per acre. In fall corn, ear size continued to increase up to and in- cluding the highest rate of N applied, which was 400 lbs per acre. The effect of 20 tons of manure per acre on average ear weight was similar to that of 400 lbs N per acre. Ear weights resulting from 10 tons manure were similar, both in spring and fall, to those resulting from 100 lbs N per acre from ammonium sulfate. There was no meas- urable effect of 5 tons of manure on ear size in the fall crop. In the spring corn, the largest increase in average ear weight came from this first 5-ton incre- ment of manure where the ear size was about the same as that produced by the 100-lb N application. Earliness Three conditions were shown to delay maturity of sweet corn. Insufficient N delayed and even prevented the matura- tion process as shown in table 1. In more than half of the seasons, sweet corn without inorganic N or manure did not reach the stage where 50 per cent of the plants produced ears which silked be- fore the crop on the average plots was harvested. Failure to apply P delayed silking by about three days. This condi- tion of insufficient P was more noticeable in spring than in fall season corn. High rates of N also delayed silking, but to a lesser extent than either of the other two conditions. Manuring, on the other hand, hastened silking by as much as three to six days in the spring crops and by one to two days in fall corn as compared to plots not receiving manure. Soil changes resulting from fertilization Several soil properties were modified as a result of fertilizing with manure or inorganic fertilizers. The accumulation of total soluble salts in the surface layer (upper 12 inches) of soil was estimated by determination of the electrical con- ductivity of soil saturation extracts. Soil samples were taken before manuring and fertilizing of each crop. The values for the various crops were averaged and are O X N MANURE O « 5 E M o 1 4 1 tj!^ r 1 >- - ^S 3NDUCTIVIT i 1 jl ( ~> o i i i ( 100 200 400 ( D 5 10 20 RATE OF N Lbs /Acre RATE OF MANURE Tons/Acre Fig. 3. The effect of nitrogen and manure fertilization on salt accumulation in the surface foot of soil. 5 10 20 RATE OF MANURE Tons/Acre Fig. 4. Bicarbonate extractable phosphorus levels in soil as affected by manure application to three, six, and nine crops of sweet corn. shown in figure 3. Manure application and inorganic N fertilization both in- creased the salinity of the surface soil. The increases in electrical conductivity resulting from application of 100 and 200 lbs N were about the same as those resulting from application of 10 and 20 tons of manure, respectively. In the fall crop samples, 20 tons of manure per acre resulted in higher salinity, than did 400 lbs of N from ammonium sulfate. Soil salinity at all levels of manure and N was always higher in samples taken before the fall crop than in those taken before the spring planting. In ad- dition, salinity resulting from the appli- cation of 20 tons of manure before the fall crop nearly always reduced the stand and retarded growth of the corn. Conductivity readings on soil samples collected after the final crop of sweet corn were much higher than correspond- ing averages of samples taken during the study. The soil reaction was not measurably altered by any of the fertilizer treat- ments and remained at approximately pH 7.9 throughout the study. Bicarbonate extractable phosphate, a measure of available P, was greatly in- 8 creased through manure application as shown in figure 4. After nine applica- tions, 10 tons of manure per acre had more than doubled the bicarbonate P level and 20 tons of manure had tripled it as compared with the nonmanured plots. After only three crops, the 10- ton application of manure had very greatly increased the available P level in the soil while 20 tons had approximately doubled it. With the 10- and 20-ton rates of application greater relative in- creases in available soil P were noted after three crops than after six or nine crops. Exchangeable soil K after nine crops was nearly tripled by application of 10 tons of manure twice yearly and quad- rupled by 20 tons per acre (figure 5). After only three crops the application of manure had approximately doubled the exchangeable K level in the soil. It is not surprising that exchangeable soil K was increased by manure application since each ton of manure contained an average of 64 lbs of K. Exchangeable calcium levels in this calcareous soil were not changed as a result of manure application, but manur- ing increased the exchangeable magne- sium and sodium levels as shown in figure 6. Exchangeable Mg, at all manure application rates, was about 10 per cent higher in samples of soil taken before the fall crop than those taken before the spring crops. After nine successive applications, 20 tons of manure, which supplied a total of 2,880 lbs of Mg, in- creased the level of exchangeable Mg in the soil about 10 per cent. Fertilization with inorganic N had no effect on ex- changeable soil Mg. Exchangeable soil Na was also in- creased by manuring. Like Mg, ex- changeable Na was higher in samples taken prior to the fall crop than in those collected before the spring crop. Twenty tons of manure per acre increased the exchangeable Na levels in the soil by about 30 per cent. Since the manure con- tained 1.6 per cent Na, 20 tons of manure would have supplied 640 lbs of Na to the soil with each application or 5,760 lbs for the total of nine applications. From soil analyses, it appears that the 600 SOIL K / Jo / & / &/ E 500 V / o. Q. 7 / 400 UJ -J 1 £/ J/ / CD / ^//^ < UJ O 300 z / VAT < I o X Ul 200 1 1 1 5 10 RATE OF MANURE Tons/Acre 20 Fig. 5. Exchangeable soil potassium as influenced by manure application to three, six, and nine crops of sweet corn. 240 o 22 ° UJ -I CD < UJ o z < I o X Ul 200 180 160 140 SOIL Mg a Na tf 1 1 — 1 1 RATE OF MANURE Tons/Acre Fig. 8. Phosphate-phosphorus (PO,-P) levels in first and second samplings of sweet corn leaf midribs as influenced by manure application. Average of nine crops. 5 10 RATE OF MANURE Tons/Acre 20 Fig. 9. Total potassium (K) levels in first and second samplings of sweet corn leaf midribs as influenced by manure application. Average of nine crops. 11 Sweet corn fertility experiment in the Coachellct Valley showing difference in earliness due to fertilization. Left (treatment 11): Plants fertilized with 400 lbs N, 52 lbs P, and 5 tons of manure per acre further advanced than treatment 12 (right) which were fertilized with 400 lbs N only. Planting sweet corn in winter in Coachella Valley. Seeding is done on the South slope of beds to gain benefits from higher soil temperatures. [12] Two rows of P-deficient sweet corn in the center. Other rows received adequate amounts of P. manure was roughly equal to 100 lbs inorganic N. The effect of manure application of P0 4 -P levels in leaf midribs is shown in figure 8. All treatments had a base rate of 52 lbs P per acre. Except for the 20- ton rate of manure, P0 4 -P in midrib tissue was higher at the second sampling than at the first. Despite the fact that manure applications greatly increased available P in the soil, soluble P levels in the plant actually decreased with the application of 5 and 10 tons of manure. This was particularly evident at the time of the second sampling. The 20-ton rate of manure halted further decrease in solu- ble P in the second sampling and resulted in an increased concentration of P in midribs at the first sampling. This was possibly due to higher available N and better growth associated with the higher levels of manure application. N deficiency is sweet corn usually appears early in Coachella Val- ley. Half-grown corn on the right received no N, that on the left received an ample supply. 1.0 £ .6 o <■> .4 .2 oNin SAMPLING 1ST SAMPLING N 100 200 RATE OF N Lbs /Acre 400 MANURE 1ST SAMPLING 2ND SAMPLING 5 10 RATE OF MANURE Tons/Acre 20 Fig. 10. The effects of manure and nitrogen fertilization on total calcium (Ca) levels in sweet corn leaf midribs. Average of nine crops. Potassium levels in sweet corn midribs were increased by manuring, as shown in figure 9. Levels at first sampling were considerably higher than corresponding second sampling levels. All values were in a range considered sufficient for this nutrient. Although fertilization had little effect on levels of exchangeable Ca in the soil, there was a small, but consistent effect on total Ca in the midrib tissue of sweet corn. As shown in figure 10, inorganic N application increased midrib Ca when compared with sweet corn receiving no N. Manuring had an opposite effect, namely that of decreasing total Ca slightly in midrib tissue in comparison with the corn receiving neither manure nor in- organic N. Total Mg levels in midribs of sweet corn receiving various rates of manure are shown in figure 11. There was an over-all decrease in plant Mg levels as manure rates were increased, despite the fact that manuring increased the supply of exchangeable Mg present in the root zone. For comparison, see figures 6 and 12. Undoubtedly, the K-Mg antagonism 5 10 RATE OF MANURE Tons/Acre Fig. 11. Total magnesium (Mg) levels in first and second samplings of sweet corn leaf midribs as in- fluenced by manure application. Average of nine crops. 14 phenomenon accounts for this depression of Mg absorption. As manure was ap- plied, the readily available K, which it contained, inhibited the uptake of Mg to the extent observed. The relation of sweet corn yields to levels of NO3-N in leaf midribs at first sampling is shown in figure 12. Data from treatments in which P might have been limiting were omitted. Very low yields were usually associated with NO3-N levels of less than 1,000 parts per million. On the basis of these and other data derived by the authors, critical levels for N in sweet corn tissue analysis are suggested below: Less than 500 ppm NO s -N: Deficient — Will respond to N 500 to 1,000 ppm NO3-N: Low — Response likely More than 1,000 ppm NO s -N: Sufficient — Response unlikely The relation of yield and leaf midrib P0 4 -P level is shown in figure 13. Data from any treatments low or deficient in N were not included. Critical levels for P in sweet corn are suggested as follows: Less than 500 ppm P0 4 -P: Deficient — Will respond to P 500 to 1,000 ppm P0 4 -P: Low — Response likely More than 1,000 ppm P0 4 -P: Sufficient — Response unlikely An additional experiment was con- ducted with sweet corn in the Coachella Valley during the spring of 1958. Meth- ods and procedures were similar to those described earlier in this bulletin. The soil was of the same type. Yields, average ear weights, and midrib N and P from the experiment conducted are shown in table 3. Steer manure was also used in this study with nutrient composition and moisture content similar to that given as an average for the nine-crop study. Nitro- gen alone at 400 lbs per acre produced higher yields than manure alone at 5 or 10 tons or 200 lbs N plus manure at either rate. Soluble N was deficient or low with inorganic N rates lower than 200 lbs per acre and with manure ap- plied at the 5-ton rate. All P values were in the intermediate range. z 1200 - 800 400 - 1 l±J ^ 200 V) SPRING FALL 1000 2000 3000 4000 5000 6000 NO3-N, ppm At 1st Sampling Fig. 12. The relation of sweet corn yield to levels of nitrate-nitrogen in leaf midribs at the first sam- pling. 1400 ■ •„ ° Z 1200 u t . • < V. . * # °o N *o ° • ° 1000 ■ • , . % m Ed 80 ° o > • f • * Z 600 • • •