Illinois
Fertilizer Conference Proceedings
January 25-27, 1993
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R.J. Lambert, R.G. Hoeft, and R.H. Teyker
The research presented in this paper developed from a greenhouse study by R. H. Teyker (1) on the response of corn inbreds to different forms and rates of nitrogen. He evaluated 28 day old seedling growth of ten corn inbreds for their response to nitrogen forms (Ca NO3 and NH4OH with nitrapyrin) and two nitrogen rates (80 mg kg-1 and 160 mg kg-1 of soil). He was able to classify the ten inbreds into three groups based on their seedling response to these variables. Inbreds LH74, C103 and LH51 preferred NO3-N over NH4-N at the 80 mg rate. Inbreds 38-11, L317, B68, and B14 preferred NH4-N over NO3-N at the 80 mg rate, but growth was suppressed at the high NH4-N rate. Inbreds WF9, LHE136, and Oh545 preferred NH4-N and had a greater tolerance to higher rates.
The objective of this field study was to evaluate the response of three corn hybrids to a factorial arrangement of supplemental-N, involving placements, rates, and forms of nitrogen. The corn hybrids involved several of the inbreds used in Teyker's study.
The experiment was planted on the Agronomy Plant Pathology farm of the University of Illinois, Urbana, IL, on May 18, 1992. The soil type was a Flanagan silt loam, with a yield potential of 140 to 150 bu ac-1. The previous crop was corn and had received 198 lbs ac-1 of supplemental-N in 1991. A previous soil test of this field showed a pH of 6.3, P1, = 52 and K1, = 356. Supplemental-N was applied eight days before planting as anhydrous ammonium with and without a nitrification inhibitor. The N was applied seven to eight inches below the soil surface. Control plots receiving no supplemental-N were used in each replicate for each hybrid. Soil samples were taken in each replicate 30 days after nitrogen application and at anthesis to assess the soil NO3-N status.
Individual plots consisted of 4 rows with rows spaced 30 inches apart, 17.5 ft. in length, and with three replications. All plots were machine planted and harvested. Plots were overplanted and thinned to a plant density of 23,869 p.p.a. No statistical differences were observed among the treatment means for percent plant stands. The three corn hybrids used were LH74 x LH51, LH 119 x Oh545 and LHE 136 x C103.
Plant and ear height and leaf length measurements were taken on five plants in each plot and plot means used in the analysis. Leaf chlorophyll content was estimated using a SPAD 502 chlorophyll meter several times during the growing season (data not shown). Before harvest a five ear sample was taken from each plot in two replications to evaluate grain yield components. The yield components measured were grain yield plant-1, ear length, kernel weight and kernels plant-1. Stalk lodging data was taken prior to harvest, and was found to vary from 0.8% to 3.07% with no affect on harvested grain.
A factorial experiment arranged in a randomized complete block design was used.
The supplemental-N rates were applied so that the placements were underneath
the row (0") and in the center of a 30 inch row (15"). The supplemental-N
rates used were 60, 120, and 180 lbs ac-1 with and without the nitrification
inhibitor. Analysis of variance procedures were used to analyze for differences
among treatment means.
Supplemental-N placement effected leaf height or early growth at the 10 to 15 leaf stage. The hybrids grown with the supplemental-N placed directly under the row (0") had an average leaf length of 144 cm compared to 134 cm for hybrids with the supplemental-N placed in the center of a 30" wide row. For leaf height an interaction was observed for supplemental-N placement x N-form. The placement of supplemental-N underneath the row average 146 cm for leaf height with nitrogen only and 142 cm for nitrogen plus the inhibitor. For the supplemental-N placement in the center of the row the hybrids had an average leaf height of 132 cm for nitrogen only but increased to 137 cm for nitrogen plus the inhibitor or an increase of 5 cm. These differences were also observed for plant height so that the average for hybrids where supplemental-N was placed underneath the row was 231 cm compared to an average of 225 cm for supplemental-N placement in the center of the row. The observed differences in leaf height and plant height may relate to some of the observed differences in grain yields.
The results for grain yield of the different factors are presented in Table 1. The average yield for all plots with supplemental-N placement underneath the row was 166 bu ac-1 compared to 149 bu ac-1 for supplemental-N placement in the center of the row or a 17 bu increase (significant at the 10% level). In this comparison a total of 54 plots were used to calculate each mean. For individual hybrids, placement of supplemental-N underneath the row produced greater yields compared to the center of the row; for LH74 x LH51 placement under the row produced 174 bu compared to 157 bu (+17) in the center of the row; for LH119 x OH545 placement underneath the row produced 183 bu compared to 160 bu (+23) in the center of the row; for LHE 136 x C103 placement underneath the row produce 140 bu compared to 130 bu (+ 10) in the center of the row.
Averaged over placements, N-forms and hybrids the supplemental-N rates of 60, 120, and 180 lbs ac-1 had an overall decrease of 10 bu. This yield decrease was 15 bu greater for N-rates when the supplemental-N was placed underneath the row compared to only 4 bu when placement was in the center of the row (Table 1). The LHE136 x C103 hybrid had the largest yield decreases with increasing supplemental-N rates with an observed decrease of 16 bu for placement over the row compared to 10 bu for placement in the center of the row. The other two hybrids (LH74 x LH51 and LH119 x Oh545) showed similar yield decreases for placement over the row but very minor decreases for placement in the center of the row (Table 1).
The high yields of the hybrid LH119 x OH545 at each supplemental-N rate and placements are difficult to explain, especially the high yields at the 60 lbs ac-1 supplemental-N rate. Some of this affect could be explained by the carry-over nitrogen of the previous crop. This is supported by the observation that the control plot for this hybrid averaged 139 bu ac-1 for the experiment.
In general the form of N used had little effect on grain yields in this experiment.
The data on grain yield components (Table 2) explains how some of these observed differences were obtained. The two yield components with greatest effect on grain yield were weight of grain plant-1 and kernels plant-1. Kernels plant-1 is usually highly correlated with grain yield plant-1. The average kernels plant-1 for supplemental-N placement underneath the row was 621 kernels plant-1 compared to 569 (significant at 10%) for hybrids with placement in the center of the row. Reductions in kernels plant-1 for all three hybrids at the two placements were also observed. For LH119 x OH545 the reduction in kernels plant-1 for under the row placement compared to the center of the row was 74 kernels plant-1, for LH74 x LH51 36 kernels plant-1, and for LHE136 x C103 45 kernels plant-1. A significant interaction of supplemental-N placement x N-form was observed, and showed that for placement underneath the row, the nitrogen only treatment produced more kernels plant-1 than nitrogen plus inhibitor (630 vs 612); for supplemental-N placement in the center of the row nitrogen only produced fewer kernels plant-1 than nitrogen plus inhibitor (553 vs 586).
Caution should be used in the interpretation of the data. The experiment was grown in only one year at one location. An abnormal amount of rainfall (estimated 15.5") occurred during July. Based on grain yields of the check plots receiving no supplemental-N a considerable amount of carry-over nitrogen was available in 1992. The hybrids used in the study were unique. The inbred parents of the hybrids had shown unique seedling response to forms of supplemental-N. Except for LH74 x LH51 none of the hybrids are being grown commercially. The data indicate unique genotypes may be developed in corn that can maximize grain yields by supplemental-N placement and be more efficient in nitrogen use.
Teyker, R. H., 1992. Influence of environment and genotype on response to enhanced ammonium supply by corn. In Proceed. of Symposium. Effects of Enhanced Ammonium Diets on Growth and Yield of Wheat and Corn. Soil Sci. Soc. of Am. Foundation for Agronomic Research, Atlanta, GA.
