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eturn to table of contents growing under stress during pollination produce ears with barren portions (examples shown in Figure 12). Portions of the cob are barren because mature ovules were not properly fertilized. These unfertilized ovules begin to disintegrate and disappear before the ear reaches physiological maturity. devoted primarily to starch and storage tissue deposition to support new plant growth when this generation of seed is planted. All kernels are attached to the cob (Figure 11), and all kernels compete for available food and water. Only those kernels that receive ample moisture and nutrients live. Typically, kernels near the butt of the ear develop a little earlier and are closer to the source of nutrients than kernels at the tip of the ear. When stress is present, the ear will often sacrifice the tip kernels in favor of kernels at the butt of the ear. Depending upon the severity of the stress, tip kernel dieback will continue until the point at which the corn plant has the ability to supply adequate water and nutrients to support growth of the remaining kernels. Normal Ear* Day 2 Day 3 Day 4 *silks exposed to pollen daily Day 5 Day 6 Day 7 Day 8 Day 9 Day 10 Day 11 Figure 11. Kernel attachment to the cob. Percent of Normal Ear Grain Harvest Wt (oz/ear) 120 100 80 60 40 20 0 Day 1 Grain Weight and Kernel Count of Ears Exposed to Pollen for One Day Field is 50% Silk on Day 4 Day 2 Day 3 Day 4 Day 5 Day 6 Day 7 Sample Day Day 8 Kernel Weight Kernel Count Day 9 Day 10 Day 11 Grain Yield Per Ear as a Function of Kernels Per Ear 8 7 y = 0.0098x 6 R 2 = 0.95 5 4 3 2 1 0 0 100 200 300 400 500 600 700 800 Kernels per Ear Kernel formation or the lack thereof is an indicator of the time of stress occurrence – whether it occurred before or during pollination or during grain fill. If a portion of the cob is barren with no evidence of viable kernel formation, the stress occurred at or before pollination. If a portion of the cob shows either very small kernels or kernel dieback, the stress occurred sometime during the grain-filling process. If tip kernels did not abort but their test weight is decreased, the stress occurred during the very latter part of grain fill. CONCLUSIONS The size, placement, and amount of corn kernel set documents when the ear was subjected to environmental stresses and the severity of these stresses. Knowledge of ear development helps agronomists and corn producers determine when stresses occurred. It also provides a starting point for developing management practices to mitigate these stresses in the future. This could lead to more complete pollination and grain fill in addition to subsequent higher grain yields. Figure 10. Relating kernel count to grain yield. ENVIRONMENTAL STRESS DURING GRAIN FILL A successfully fertilized kernel goes through two phases in the approximately eight weeks between pollination and physiological maturity. For approximately the first three weeks after pollination, embryo cells are rapidly differentiating and dividing to produce the tissues necessary for the embryonic corn plant contained within the kernel. The remaining weeks of grain fill are Figure 12. Stress during grain fill very often results in tip kernel dieback or some sort of kernel abortion. 36

eturn to table of contents IMPACT OF CORN STOVER HARVEST ON SOIL PROPERTIES AND PRODUCTIVITY by Francisco J. Arriaga, Ph.D., Assistant Professor, Department of Soil Science, University of Wisconsin-Madison BACKGROUND • With the increasing demand for non-petroleum based fuels, corn stover presents a potential raw material for ethanol production. • Corn stover provides various benefits to soil, including the cycling of nutrients and soil organic matter. Removing this resource for use in ethanol production could affect soil function and crop productivity in the future. • Previous studies have shown a negative to neutral impact of removing stover from fields; therefore, understanding the response of specific soil types to stover removal is important in making recommendations to producers. These impacts have not been studied in detail in Wisconsin soils. OBJECTIVES • Evaluate the effect of stover harvest on corn productivity and its influence on nitrogen fertilization rates. • Determine the impact of corn stover harvest on soil properties. STUDY DESCRIPTION Years: 6 (2010-2015) Locations: Arlington, WI (Plano silt loam) Lancaster, WI (sloped Fayette silt loam) Replications: 4 Factors: • Nitrogen Application Rates: »» 0 lbs/acre » 150 lbs/acre »» 50 lbs/acre » 200 lbs/acre »» 100 lbs/acre » 250 lbs/acre • Stover Removal Rates: »» 0% » 50% » 100% • Plots at both locations were fall chiseled followed with a soil finisher in the spring. • Soil samples were collected for bulk density, nutrient, and organic matter analysis. RESULTS - IMPACT ON YIELD • Stover removal effects on grain yields during the six growing seasons at Arlington were sporadic, often occurring in the nitrogen rates that were lower than the UW-Extension recommended annual application rate of 150 lbs N/acre (Figure 1). Corn Yield (bu/acre) 250 200 150 100 50 Stover Removal Rate 0% 50% 100% 0 0 50 100 150 200 250 Nitrogen Rate (lbs N/acre) Figure 1. Average (2010-2015) corn grain yield in Arlington as influenced by nitrogen application rate and stover removal rate. Corn Yield (bu/acre) • Stover removal effects on grain yield at Lancaster were also sporadic and only occurred in plots that were fertilized with rates less than the UW-Extension recommended rate (Figure 2). 250 200 150 100 50 Stover Removal Rate 0% 50% 100% 0 0 50 100 150 200 250 Nitrogen Rate (lbs N/acre) Figure 2. Average (2010-2015) corn grain yield in Lancaster as influenced by nitrogen application rate and stover removal rate. RESULTS - IMPACT ON SOIL PROPERTIES • Soil nitrate-nitrogen content from 0 to 2-foot depth at corn emergence from the 150 lb/acre nitrogen fertilization rate was similar between corn stover removal rates within years at the Arlington site (Table 1). • At Lancaster, soil nitrate-nitrogen contents were similar between stover removal rates during the first three growing seasons. During the last three growing seasons (2013-2015) at Lancaster, nitrate-nitrogen was lower in the 100% removal rate, but overall nitrate contents were generally low (Table 1). 37

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