Summer pulses as sources of green manure and soil cover in the U.S. Southern Great Plains

Abstract

Winter wheat (Triticum aestivum L.) – summer fallow rotations in the Southern Great Plains (SGP) have numerous sustainability issues, such as low precipitation use efficiencies and increased soil erosion. Replacing summer fallow with a legume grown as a green manure would help reduce soil erosion, improve precipitation use efficiency, and add nitrogen (N) credits for the subsequent wheat crop. A two-year field experiment evaluated the capabilities of three summer pulses: soybean [Glycine max (L.) Merr.], moth bean [Vigna aconitifolia (Jacq.) Marechal], and tepary bean [Phaseolus acutifolius (A.) Gray] to serve as green manures and soil cover. We examined their performance across two row spacings (38 and 76 ​cm) and two moisture regimes (rainfed and irrigated). Narrow row spacing (38 ​cm) provided greater canopy cover, aboveground biomass, and N accumulation than the broad row spacing (76 ​cm) during the early growing season. Among species, tepary bean demonstrated consistent and higher canopy cover early in the season. Soybean produced the highest aboveground biomass (5,327–8,855 ​kg ​ha−1) and N accumulation (115–269 ​kg ​ha−1) among the three pulses. Multilinear regression (MLR) models suggested that canopy height and canopy cover could estimate both aboveground biomass (R2 ​= ​0.62) and N accumulation (R2 ​= ​0.55) for tested pulses. Based on results, soybean was the most promising choice among tested pulses, considering its higher aboveground biomass and N accumulation. Modelling studies to simulate growth of these crops with long-term weather scenarios are encouraged to identify the most reliable cover crop for different areas of the SGP.