Moth bean and tepary bean as green nitrogen sources in intensive winter wheat cropping systems

Use of cover crops have been suggested to increase agricultural sustainability by providing multiple ecosystems services. Replacing summer fallow with drought tolerant legumes could serve both as a cover and a green source of N for winter wheat (Triticum aestivum L.) and help mitigate economic and environmental problems by increasing resilience of agroecosystems in the United States (US) Southern Great Plains (SGP). Field experiments were conducted in 2018 and 2019 at the USDA ARS Oklahoma and Central Plains Agricultural Research Center near El Reno, OK. The overall objective of the study was to quantify the potential of two summer legumes, tepary bean [Phaseolus acutifolius (A.) Gray] and moth bean [Vigna aconitifolia (Jacq.) Marechal], as green sources of N for winter wheat production in comparison with soybean [Glycine max (L.) Merr.]. The PROC MIXED procedure of the SAS statistical software was used to analyze biomass production by legumes, their impacts on soil water, soil N and yield of winter wheat, and N transfer from green N biomass to following winter wheat. Green N crops did not differ in biomass production, but soybean provided 22 % and 40 % more N than tepary bean and moth bean, respectively. Soil water was reduced under all green N crops than summer fallow at termination of green N crops and wheat planting. Biomass of green N crops increased N content in soils at wheat planting. Grain yield of winter wheat was significantly higher under tepary bean (5295 kg ha-1) than soybean (4300 kg ha-1), moth bean (4560 kg ha-1) and the control treatment (4323 kg ha-1). Nitrogen recovery in wheat biomass was greater under moth bean and tepary bean compared to soybean. Both moth bean and tepary bean could serve as green sources of N for winter wheat in the US SGP.