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Fluid Journal : Fluid Journal 1999-2001
2 Fluid Journal Summer 2001 plant populations, and fertilizer require- ments needed to achieve yields that approach the crop's potential. Primary objectives during the first two years of this research were to: • Establish a long-term experiment in which several key factors govern- ing optimal soil productivity and yield potential of corn and soy- beans can be identified • Quantify crop nutrient uptake requirements, crop growth rates, leaf area, and root development needed to achieve yield potential levels • Determine the C sequestration potential of cropping systems that consistently produce yields near the yield potential levels, measure N, P, and S composition of the newly formed humus, and estimate the rate of organic matter turnover in these systems • Validate appropriate crop simulation models that accurately predict the yield potential of corn and soy- beans in different years and locations with different climatic regimes. Results reported are preliminary as many of the comprehensive soil and plant analyses performed are still in progress. These experiments began in 1999, following a soybean crop. 1999 As shown in Figure 1, grain yields ranged between a low of 162 bu/A for the unfertilized control (30,000 plants/A) and 258 bu/A for intensive management (M2) treatment at a high population (44,000 plants/A). The M2 treatment significantly increased yield at all population levels, resulting in an average grain yield increase of 25 bu/A over the recommended fertility regime (M1). Grain yield also increased linearly with population. An average difference of 11 and 22 bu/A was observed by increas- ing population from 30,000 to 44,000 plants/A for the M1 and M2 fertility regimes, respectively. Fertility manage- ment had a significant effect in reducing the percentage of barren stalks, as shown in Figure 2. Stover yield increased with both an increase in population and fertility management and ranged from 3.44 tons/ A in the control to 5.5 tons/A under intensive management having a population density of 44,000 plants/A (Figure 3). This resulted in a significant increase in the amount of carbon added to the soil in corn residue under intensive management (Figure 4), which we hypothesize will result in improved soil quality and a greater capacity for this soil to sustain high yields under intensive management in future years. Harvest index (grain yield/total biomass yield) of the 1999 corn crop was near the maximum published values observed for maize and averaged 0.55 across population and management treatments (Figure 5). 2000 We were able to compare the effects of crop rotation as an additional treatment. Corn grain yield in 2000 was not as we anticipated. We observed an average yield increase of 14 bu/A due to the previous soybean crop in the fertilized treatments (Figure 6). The M2 treat- ment resulted in a significant but smaller yield increase over the M1 treatment (8 bu/A) than observed in 1999. Averaged across population, grain yield was highest at 37,000 plants/A by approxi- mately 8 bu/A. We anticipated a much higher yield in 2000 than in 1999, based upon observed crop development. Vegetative (leaf and stalk) development averaged 12 percent higher in 2000, with the greatest PLANT POPULATION DENSITY (pl/A) Figure 4. Population and management effects on Carbon returned to soil in crop residue, 1999. CARBON IN STOVER (ton/A) 30,000 37,000 44,000 3 2 1 0 CONTROL RECOMMENDED (M1) INTENSIVE (M2) PLANT POPULATION DENSITY (pl/A) Figure 5. Population and management effects on corn harvest index, 1999. 30,000 0 0.2 HARVEST INDEX 0.4 0.6 37,000 44,000 CONTROL RECOMMENDED (M1) INTENSIVE (M2) CONTINOUS CORN CORN AFTER BEAN CONTROL RECOMMENDED INTENSIVE 300 250 200 150 100 30,000 Figure 6. Population and management effects on corn grain yield, 2000, PLANT POPULATION DENSITY (pl/A) CORN GRAIN YIELD (bu/A) 37,000 44,000 30,000 37,000 44,000
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