Abstract
Scientists and farmers have been evaluating the intercropping of soybean [Glycine max (L.) Merr.] into wheat (Triticum aestivum L.) before harvest as an alternative to doublecropping in the lower Midwest. It was our objective to examine the interrelationships of soybean row spacing, planting date, and N applied to wheat in a wheatsoybean intercropping system. The experiment was conducted near Columbia, MO, in 1983, 1984, and 1985, on a Mexico silt loam (Udollic and Mollic Ochraqualf). Whole-plot treatments consisted of two cropping systems (conventional and intercropped), drilled and skiprow planting patterns (0.2- and 0.8-m row spacings of soybean), and three soybean planting dates coinciding with wheat growth stages. Subplots consisted of spring applied N treatments (0, 56, and 112 kg ha−1). A wheat-soybean double crop was also included. Wheat yields were reduced 23 and 16% when soybean was intercropped in the drilled and skiprow patterns, respectively. The date of planting did not significantly (P < 0.05) influence wheat yield in the skiprow patterns. However, wheat yield was significantly (P < 0.05) decreased as planting date was delayed in the drilled pattern because of mechanical damage. Intercropped soybean yielded 27% less than conventional soybean but 28% more than doublecropped soybean over all years and treatments. Drilling soybean at the heading stage of wheat resulted in greatest yields. In 1985, N applied in excess of 56 kg ha−1 produced excessive wheat vegetative growth resulting in competition for light which caused a reduction in drilled, intercropped soybean yield. Where mechanical damage to wheat can be minimized, drilling soybean in wheat at heading can result in optimum intercrop performance. Copyright © . .