Wheat (Triticum aestivum L.) Cultivar Selection Affects Double-Crop and Relay-Intercrop Soybean (Glycine max L.) Response On Claypan Soils.

Field research (2003-2005) evaluated the effect of wheat row spacing (19- and 38-cm) and cultivar on double-cropped (DC) response, 38-cm wheat on relay-intercrop (RI) response, and wheat cultivar selection on gross margins of these cropping systems.  Narrow-row wheat increased grain yield 460 kg ha^-1, light interception (LI) 7%, and leaf area index (LAI) 0.5 compared to wide rows, but did not affect DC soybean yield.  High yielding wheat (P25R37) with greater LI and LAI had lower (330 kg ha^-1) soybean yields in a RI system than a low yielding cultivar (Ernie).  Gross margins were $267 ha^-1 greater when P25R37 was RI with H431 Intellicoat (ITC) compared to Ernie.  Gross margins were similar for monocrop H431 non-coated (NC) or ITC soybean, P25R37 in 19- or 38-cm rows with DC H431 NC soybean, and P25R37 in 38-cm rows with RI H431 ITC soybean in the absence of an early frost.