Experiments at the North Willamette Experiment Station in 1979 and 1980 indicated that, for N applied as ammonium nitrate at 160 pounds N/acre, sweet corn yields were increased by delaying application of most of the N until the corn was 10 to 12 inches tall. These experiments were at fairly high levels of early season irrigation, and the lower yields when all N was applied at planting may have been caused by leaching of nitrate-N out of the root zone. In a trial in 1984, however, splitting the N application did not increase yield with ammonium nitrate as N source. In addition, application of N as urea or urea plus ammonium chloride did not increase yields over those with ammonium nitrate, indicating no leaching of nitrate.
The objective of the 1985 trial was to compare the yield response of sweet corn to three rates of N, applied as either ammonium nitrate or urea, with all N applied at planting. In addition, three rates of split application of ammonium nitrate, with three methods of application (surface banded, subsurface banded, irrigation water) were compared. In 1986, yield of sweet corn was studied as a function of N rate and form, a nitrification inhibitor, and timing of N application.
Methods
1985
'Jubilee' sweet corn was seeded in a Willamette silt loam, pH 5.8, on May 14, 1985, following a broadcast application of potassium sulfate at 85 pounds K/acre. Plot size was 4 rows x 40 feet, between row spacing 30 inches, and plant population about 28,000/acre. Forty pounds N and 120 pounds P205/acre (13-39-0) was banded 2 inches below and two inches to the side of the seed row at planting on all plots. In addition, treatments 1, 2, and 3 received an additional 60, 120, or 180 pounds N/acre, respectively, as ammonium nitrate broadcast at planting. Treatments 4, 5, and 6 received an additional 60, 120, or 180 pounds N/acre, respectively, as urea, also broadcast at planting. Treatments 7, 8, and 9 received a surface banded application of ammonium nitrate on June 26, when the corn was about 12 inches tall. The N rates were 60, 120, and 180 pounds/acre, respectively. Treatments 10, 11, 12 received a subsurface banded application of ammonium nitrate on June 26 at the above rates. For treatments 13, 14, and 15, the three rates of N were applied on June 26, after the appropriate amounts of ammonium nitrate were dissolved in 5 gallons of water. Application was from sprinkler cans to simulate the effect of applying N through the irrigation system. Treatments were replicated four times in randomized complete block design.
Although it was a dry spring and soil moisture was low, the stand was not irrigated up, in order to maintain normal grower irrigation practices. Leaf samples were taken for tissue analysis on July 22, at first tasseling. All ears were harvested from 20-foot sections of the center two rows of each plot on August 22 and were graded as mature, immature, or culls. Culls were not included in yield measurements.
1986
Methods were as in 1985 except that treatments 1,2,and 3 received an additional 60 pounds N/acre as ammonium nitrate, urea, or urea plus DCD-treated urea (2:1 ratio), broadcast at planting (May 29). The DCD-treated urea contained 7.2 percent dicyandiamide. Treatments 4, 5 and 6 received an additional 60 pounds N/acre ammonium nitrate, urea, or urea plus DCD-treated urea (2:1 ratio) sidedressed on July 8. Treatments 7-12 received the above forms of N and timing of N application, but the additional N applied was 160 pounds/A (200 pounds total N/acre). Treatments were replicated four times in randomized complete block design.
The stand was irrigated up to assure even emergence. Harvest was on September 3.
Results
1985
Total ear yield (sum of mature and immature ears), mean ear weights, and ear lengths varied significantly with treatment (Table 1). However, the main effects of N rate, method of placement and timing, and N source were not statistically significant except that total yield was reduced with urea as compared to ammonium nitrate, and mean weight of mature ears increased with increasing N rate (Table 2). Both leaf tissue N and Ca concentrations increased significantly with increasing rate of N (Table 3). Nitrogen source and application method had no effect on leaf N and Ca concentrations and there were no significant interactions. Only the main effects of N rates are given in Table 3. Leaf tissue P, K, and Mg concentrations were not affected by treatment (data not shown).
This experiment provided no evidence for any yield differences attributable to timing or method of placement of N. A combined ammonium and nitrate source of N gave yields equal or superior to those with a source containing no nitrate. Since 1985 was a very dry year, with only 4.3 inches precipitation between planting and harvest, leaching of nitrate-N was probably negligible.
Table 1. Effects of rate, source, timing, and placement of N on sweet corn yield, 1985 Treatment Total N SourceZ Application Ear yield Mean ear weight Ear number applied of N method Mature Total Mature Total length lb/A --tons/acre-- ----pounds----- inches 1 100 Am. nitr. surfaceY 6.4 8.6 0.76 0.72 8.8 2 160 Am. nitr. surfaceY 6.9 8.6 0.74 0.72 9.1 3 220 Am. nitr. surfaceY 7.5 9.3 0.77 0.72 9.4 4 100 Urea surfaceY 6.3 8.1 0.78 0.74 9.0 5 160 Urea surfaceY 5.9 7.4 0.78 0.72 8.9 6 220 Urea surfaceY 6.1 7.9 0.79 0.72 8.7 7 100 Am. nitr. surfaceX 5.9 8.0 0.78 0.70 8.8 8 160 Am. nitr. surfaceX 8.1 9.5 0.77 0.73 8.8 9 220 Am. nitr. surfaceX 6.9 8.7 0.80 0.74 9.0 10 100 Am. nitr. subsurfaceX 7.5 9.5 0.78 0.70 8.9 11 160 Am. nitr. subsurfaceX 7.4 9.5 0.77 0.70 8.8 12 220 Am. nitr. subsurfaceX 7.5 9.9 0.79 0.72 9.3 13 100 Am. nitr. sprinklerX 5.6 7.5 0.76 0.70 9.2 14 160 Am. nitr. sprinklerX 7.0 8.7 0.78 0.72 9.0 15 220 Am. nitr. sprinklerX 7.2 9.3 0.83 0.77 9.1 LSD(0.05) NS 0.7 0.06 0.06 0.6 ZAll plots received 40 pounds N/acre as 13-39-0 at planting. YAll N applied at planting. XBulk of N applied on June 26. NS: no significant differences. Table 2. Main effects of N source on total ear yield and main effect of N rate on mean ear weight of mature ears, 1985 N source Total yield N rate Mean ear weight (tons/acre) (pounds/acre) of mature ears (pounds) Amm. nitrate 8.9 100 0.77 Urea 7.8 160 0.77 *Z 220 0.80 * Z*: significant differences among means at 5% level. Table 3. Main effects of N rate on leaf tissue N and Ca concentrations, 1985 N rate (pounds/acre) Leaf N (%) Leaf Ca (%) 100 3.13 0.68 160 3.30 0.71 220 3.35 0.74 **Z * ______________________________________________ Z**,*: significant differences at 1% and 5% levels, respectively.
1986
Total ear yield, mean ear weights, and ear lengths varied significantly with treatment (Table 4). However, the main effects of timing of application and N source were not statistically significant. Increasing the N rate from 100 to 200 pound/acre increased total yield and ear length and tended to increase ear weight and yield of mature ears (Table 5).
This experiment provided no evidence for any yield differences attributable to timing of application or source of N. A combined ammonium and nitrate source of N gave yields essentially equal to those with a source containing no nitrate. The presence of a nitrification inhibitor also did not affect yield. 1986 was, again, a very dry year, with only 1.7 inches precipitation between planting and harvest. Leaching of nitrate-N was probably negligible. Nitrate-N may be lost more readily in early plantings in wet springs and if irrigation is not kept to the minimum required for adequate plant growth.
Table 4. Effects of N rate, source, and timing of N application on sweet corn yield, 1986 Treatment Total N Source Timing of N Ear yield Mean ear wt. Ear number applied of N application Mature Total Mature Total length lb/A --tons/acre-- ---pounds---- inches 1 100 Am. nitrate planting 8.8 9.3 0.63 0.61 8.2 2 100 Urea planting 9.7 10.0 0.70 0.69 8.1 3 100 Urea-DCD planting 9.4 10.0 0.66 0.63 8.1 4 100 Am. nitrate split 8.7 9.2 0.68 0.67 8.2 5 100 Urea split 8.9 9.3 0.64 0.63 8.3 6 100 Urea-DCD split 10.1 10.2 0.66 0.66 8.0 7 200 Am. nitrate planting 9.9 10.5 0.67 0.67 8.5 8 200 Urea planting 9.8 10.2 0.69 0.68 8.6 9 200 Urea-DCD planting 10.8 11.0 0.70 0.69 8.4 10 200 Am. nitrate split 9.6 10.1 0.67 0.67 8.4 11 200 Urea split 9.8 10.3 0.65 0.64 8.3 12 200 Urea-DCD split 8.7 9.2 0.65 0.65 8.4 LSD(0.05) NS 1.3 0.05 0.05 0.5 Table 5. Main effects of N rate, source, and timing of application on sweet corn yield, 1986 Ear yield Mean ear weight Ear Treatment Mature Total Mature Total length --tons/acre-- -----pounds---- inches Amm. nitrate 9.3 9.8 0.66 0.65 8.3 Urea 9.5 9.9 0.67 0.66 8.3 Urea + DCD 9.8 10.1 0.67 0.66 8.2 NSZ NS NS NS NS 100 lb N 9.3 9.7 0.66 0.65 8.2 200 lb N 9.8 10.2 0.67 0.66 8.4 NS * NS NS * planting 9.7 10.1 0.67 0.66 8.3 split 9.3 9.7 0.66 0.65 8.3 NS NS NS NS NS ZNS, *: means do not differ significantly, and significant differences between means at the 5% level, respectively.