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Fluid Journal : Fluid Journal 2002-2004
2 Fluid Journal Summer 2002 and soil management will be necessary to coax more out of the crop biomass potential. In this article, focus will be on a more detailed understanding of corn yields, as well as soil processes regarding carbon sequestration at different cropping intensity. Yields improved Plant density and nutrient management levels significantly affected yield, harvest index, stover yield, components of yield, and nutrient uptake requirements of corn. Intensive fertilizer management (M2) significantly increased yield in all three years over the recommended fertility regime (M1) as shown in Figure 1. Maximum grain yields ranged from 249 to 257 bu/A in all three years of the study. In all three years, treatment CS- M2-P2 produced consistently high yields of 245 to 252 bu/A that were close to the simulated yield potential for this plant density (Figure 1). Continuous corn yields were below those obtained in the corn/soybean rotation at the recommended level of nutrient management (M1), but the differences diminished for M2 nutrient management. 1999. Corn was planted late (May 13) and grain yield increased with both increasing population density and management intensity, with a high of 258 bu/A for the CS-M2-P3 treatment. At the M2 level of nutrient management, the harvest index of maize decreased with increasing plant density due to greater vegetative biomass accumulation. Sink size (number of kernels/m2) and nutrient uptake also increased with increasing plant density and nutrient management level. The 100-seed weight was about 4 percent larger in M2 treatments than in M1, but decreased with increasing plant density. 2000-2001. Corn was planted in late April and growth was much affected by hot temperatures during grain filling. Highest yield was 249 bu/ A in 2000 (CS-M2-P2 treatment) and 252 bu/A in 2001 (CS-M2-P2 and CC- M2-P3 treatments). In 2000, at all population and nutrient management levels, grain yield in continuous corn Table 1. Nutrient accumulation per unit grain yield as affected by fertility management (M) and plant density (P). Averages of 1999 and 2000, corn after soybean. Plant NPK---lbs/A Yield N P2O5 K2O Mg S population bu/A lbs nutrient/bu/A yield Aboveground nutrient uptake P1 M1 UN-L-rec (120-0-0) 224 1.06 0.43 1.55 0.10 0.12 P2 M2 intensive (234-92-93) 247 1.08 0.42 1.76 0.10 0.11 P3 M2 intensive (234-92-93) 247 1.12 0.41 1.84 0.10 0.11 Nutrient removal with grain P1 M1 UN-L-rec (120-0-0) 224 0.69 0.32 0.22 0.05 0.06 P2 M2 intensive (234-92-93) 247 0.68 0.32 0.23 0.05 0.06 P3 M2 intensive (234-92-93) 247 0.67 0.31 0.22 0.05 0.05 Figure 2. Comparison of estimated total C input to soil from 1) aboveground crop residues after grain harvest and 2) roots, after two years (1999 to 2000) in continuous corn (CC) and corn/soybean (CS) in M2 nutrient management and P2 plant densities. Total C recycled into soil (ton/acre) 3.0 3.5 4.0 4.5 5.0 5.5 6.0 6.5 CC CS was below that of corn grown after soybeans, but the difference was smallest in M2 treatments. Similar observations were made for M1 treatments in 2001, but corn yield in M2 treatments with high plant density was similar in the CC and CS rotations (Figure 1). Increasing plant density beyond the P2 level did not significantly increase yield and plant nutrient accumulation in 2000 and 2001, or even lead to the decrease observed in 2000. Actual plant densities in the P3 treatment were about 5 percent greater than in 1999 (P3: average of 46,500 plants/A in 2000 and 2001 vs. 44,200 plants/A in 1999), which may have further accelerated crop stress under high temperatures during grain filling. Biomass x temperature interactions on crop respiration losses may explain why in 2000 and 2001 yields did not increase in the highest density treatment because the actual plant density in P3 was probably excessive, whereas it was already near optimal (37- 41,000 plants/A) in the P2 treatment. At the intensive level of nutrient management, harvest index of maize decreased with increasing plant density due to greater vegetative biomass accumulation. Stover yield (stalks, leaves, cobs, tassels) increased with increases in both population and fertility management. For example, averaged over three years, stover yield was 6.8 tons/A dry matter in corn after soybeans at the currently recommended plant density (P1, 30,000 plants/A) and fertilizer management level (M1). By contrast, stover yield at very high density (P3) and intensive fertilizer
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