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Fluid Journal : Fluid Journal 1999-2001
3 Fluid Journal Summer 2001 treatment effects in continuous corn (Figure 7). However, the highest grain yield achieved in 2000 was treatment M2 following soybeans, producing 248 bu/ A at 37,000 plants/A. The resulting harvest index was well below the 1999 level and averaged 0.50 for fertilized corn (Figure 8). We believe the lack of a larger yield response, despite greater total dry matter production in 2000 compared to 1999, resulted from the unusually rapid grain filling rate due to high tempera- tures after silking in 2000. Total time Table 1 Fertilizer rate and timing applied to corn. N (lbs/A) Treatment Growth stage 1999 2000 Corn/soybean, M1 Preplant 58 92 V6 58 31 M2 Preplant 94 92 V6 54 89 V10 54 85 Corn M1 Preplant 92 V6 89 M2 Preplant 92 V6 116 V10 116 M1: no additional nutrients applied. M2: 44P-75K-20S-10Fe-5Zn applied preplant. from silking to black layer formation was 11 days shorter in 2000 compared to 1999, which provided a considerably shortened grain filling period. Simula- tion of crop growth using crop growth models gives credence to this hypoth- esis. With normal temperatures and a more typical length of grain filling, grain yields in 2000 should have surpassed the best yields obtained in 1999. Methodology Soil. The long-term experiment was established on a deep Kennebec silt loam (Cumulic Hapludoll). Soil test values to 8-inch depth were: pH 5.3, buffer pH 6.6, OM (%) 2.7, Bray ext. P (ppm) 67, and exch. K (ppm) 366. Plots. Treatments were arranged in a split/split plot design. Crop rotations (continuous corn vs corn/soybeans) were main plots. Three plant popula- tions planted in 30-inch rows were subplots. Level of fertilizer nutrient inputs was sub-subplots. Fertilization. Initial applications of N, P, K, S, Fe, and Zn were applied preplant and incorporated prior to planting by disking. Subsequent N splits were surface broadcast and then irrigated into the soil. Table 1 shows N rates. Lime was applied in fall of 1999 at 2 tons CCE/A. The authors of this report are research- ers for the Department of Agronomy at the University of Nebraska. CONTINUOUS CORN CORN AFTER BEAN PLANT POPULATION DENSITY (pl/A) Figure 8. Population and management effects on corn harvest index, 2000. 0.6 0.6 0.4 0.4 0.2 0.2 0 0 30,000 30,000 37,000 37,000 44,000 44,000 HARVEST INDEX HARVEST INDEX CONTROL RECOMMENDED (M1) INTENSIVE (M2) CONTINOUS CORN CORN AFTER BEAN CONTROL RECOMMENDED (M1) INTENSIVE (M2) 7 6 5 4 3 2 1 0 30,000 Figure 7. Population and management effects on stover yield, 2000. PLANT POPULATION DENSITY (pl/A) STOVER YIELD (ton/A) 37,000 44,000 30,000 37,000 44,000
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