Form and Timing of Applied Nitrogen on Sweet Corn Production (1984)

Recent experiments at the North Willamette Station indicated that, for a given level of N, yields are increased by delaying application of the bulk of the N fertilizer until the corn is 10 to 12 inches tall. These experiments used ammonium nitrate as N source and the late applied N was sidedressed on the soil surface. No additional benefit was obtained by delaying application of a portion of the N until tasseling or silking. The yield increase with split application of N could be from leaching of NO3-N below the root zone when all N is applied at planting. Some N also could be volatilized. One purpose of the 1984 experiments was to determine whether application of all N at planting would produce yields equal to those with a split application if an N source other than ammonium nitrate were used.

Methods

'Jubilee' sweet corn was seeded in a Willamette silt loam, pH 5.8, on. May 17, 1984. Plot size was 6 rows x 40 feet and spacing between rows was 30 inches. Thirty pounds N and 150 pounds P205/acre, as 11-55-0 ammonium phosphate were banded 2 inches below and Z inches to the side of the seed line at planting. In addition to the above, Treatments 1, 2, and 3 received 40, 100, or 160 pounds N/acre, respectively, as ammonium nitrate banded 2 inches below and 6 inches to either side of the seed line on July 3. Treatments 4, 5, and 6 received 100 pounds N/acre as ammonium nitrate, 100 pounds N/acre as urea (46-0-0), or 50 pounds N/acre as urea plus 50 pounds N/acre as ammonium chloride, respectively, banded 2 inches below and 6 inches to either side of the seed line at planting. Total N applied, form of N, etc. are summarized in Table 1. Herbicide and irrigation practices were normal for sweet corn in the Willamette Valley. First irrigation occurred on July 11.

Initial stands did not vary significantly with treatment and all plots were thinned to the desired average spacing of 1.5 plants/foot or about 26,000 plants/acre on June 12. All ears were harvested from 30-foot sections of the center 2 rows of each plot on September 5. Ears were graded as fully mature, immature, or culls.

Results and Discussion

Yield increased with increasing rate of ammonium nitrate-N, when N application was split (Table 1, Treatments 1-3). In comparing Treatment 2 (split application of ammonium nitrate at 130 pounds N/acre) with Treatment 4 (all ammonium nitrate at planting), there was no advantage to splitting the N application. This is in contrast to experiments in 1979 and 1980, in which splitting the ammonium nitrate application increased yields.

The lack of yield advantage in 1984 may have been from reduced leaching of nitrate. Also, all N in the earlier experiments, except for the 40 pounds/acre banded with P, was surface applied. Some loss to the atmosphere may have occurred when up to 160 pounds N/acre was applied to the soil surface in 1979 and 1980. In contrast, in 1984, all N, whether at planting or in July, was banded beneath the surface. Another possible explanation for the lack of advantage for split application in 1984 is that the subsurface banding in July may have caused root pruning and temporary stunting of plant growth. Application of N as urea or urea plus ammonium chloride did not increase mature or total ear yield over yields with ammonium nitrate (Treatments 4-6), indicating no leaching of nitrate.

Mean ear weight did not vary greatly with treatments, but the trends were the same as for ear yields. Ear weights were lowest at the low rate of N and N source did not affect ear weight.

In summary, this experiment has confirmed previous results concerning response of corn yields to rate of N but did not confirm previous evidence for the advantage of splitting N applications. No evidence was obtained which would indicate an advantage for any particular N source.

Table 1. Effects of N rate, source, and timing of application on sweet corn yield, 1984     Treatment  Total N     N source     Time of applic.  Mature ear  Total earZ   Mean ear wt.  number     applied  in 6-inch band  of N in 6-in.band  yield       yield     Mature  Total              lb/A                                        T/A         T/A	     -----lb------  1            70     Am. nitrate        July             7.6	    9.4      0.74     0.69  2           130     Am. nitrate        July             9.3	   10.8      0.79     0.75  3           190     Am. nitrate        July            10.0	   11.2      0.76     0.74  4           130     Am. nitrate        at planting      9.8	   10.5      0.76     0.74  5           130     Urea               at planting      8.4	   10.5      0.78     0.73  6           130     Urea+Am. chloride  at planting      8.9        11.0      0.76     0.70                                               LSD(0.05)  1.9         1.2      0.03     0.05  ZDoes not include culls.  

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