Thesis (M.S.)--University of Wisconsin--Madison, 1983. / Typescript. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 90-97).

With the recent rise of wheat (Triticum aestivum L.) prices and the spike in cotton (Gossypium hirsutum L.) prices in 2011, a renewed interest in double-cropping cotton following wheat production occurred. Research was established to improve production practices of double-cropped cotton at three Mississippi locations, Starkville (2012-2013), Brooksville (2012-2013), and Stoneville (2013). Cotton following wheat has the potential to result in a higher return compared to soybeans; however, the financial risk associated with cotton is far greater than with soybeans. Growers should increase seeding rates by 20% when double-cropping cotton following wheat and burn the wheat stubble to maximize yield. No definitive N rate was observed to maximize yield; however, a normal rate full-season cotton is not recommended as high N rates delayed maturity and increased the potential yield loss.

Demand for potassium (K) increases with increasing soybean yield. Little research has been conducted on soybean response to K on coastal plain and piedmont soils of Virginia, especially in double-crop systems. Nineteen full-season and 14 double-crop soybean experiments were conducted in 2013 and 2014 in Virginia and northeastern North Carolina to determine full-season and double-crop soybean (with wheat straw remaining or removed) response to soil test K and K fertilizer application rates. Field moist, air dried, and oven dry soil test K extraction techniques were also compared to predict responsiveness of sites to K applications. Potassium fertilizer increased yield in five of 19 full-season experiments and one of 14 double-crop experiments. Full-season soybean yield plateaued at 88% relative yield and soil test K value of 38.8 mg K kg-1. Full-season plant K critical concentrations were 18.2 g K kg-1 for V5 and 24.6 g K kg-1 for R2. Although critical concentrations could not be determined for double-crop soybean, V5 and R2 concentrations ranged from 17.6 to 35.6 g K kg-1 or 13.2 to 28.1 K kg-1, respectively, most of which were within or above accepted sufficiency levels. Eight of 13 sites resulted in greater soil K concentrations when alternative soil drying methods were compared to air-dry methods. However, differences were not consistent and no single method was superior for these soils. More data is needed for double-crop soybean systems due to lack of response and lack of low soil test K sites in these experiments. / Master of Science

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