Soybean‐Wheat Doublecropping: Implications from Straw Management and Supplemental Nitrogen' 1

Doublecropped soybean [ Glycine max (L.) Merr.] following winter wheat ( Triticum aestivum L.) is usually planted past the optimum date for monocropped beans. To make good yield, early growth of doublecropped soybean is very important. The purpose of this experiment was to determine wheat straw leachate, wheat straw management, and supplemental N effects on soybean germination, growth, and yield. Leachate concentrations of 0, 20, and 100 g L −1 (straw to deionized water) were used for germination and radicle growth studies. Leachate concentrations of 0, 2, and 20 g L −1 were used in sand culture and the Ap horizon of Okolona silty clay (fine, montorillonitic, thermic Typic Chromudert) to study germination and early growth of soybean. A 3‐yr experiment on Okolona silty clay, consisting of six management practices and two N levels (0 and 28 kg ha −1 ), was used to study soybean growth and yield in the field. Management practices consisted of monocropped soybean planted near the optimum date and at the doublecropped date and doublecropped soybean planted where wheat straw was either burned, physically removed, soil‐incorporated, or left standing. Germination was not significantly affected by leachate but was reduced by late planting in the field. The 100 g L −1 leachate inhibited radicle growth, while 20 g initially inhibited but then stimulated radicle growth. The 20 g L −1 leachate inhibited early growth in the laboratory but only in the silty clay, while the 2 g L −1 leachate stimulated growth, especially in the sand. Wheat straw inhibited growth and yield in the field. Supplemental N was most effective in overcoming depressed growth and yield where straw was left on the soil surface. Early monocropped soybean produced the largest average yield, but doublecropped soybean where straw was burned produced the greatest economic returns.