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

Authors: SINGH, HARDEEP - Kansas State University; Northup, Brian; GOWDA, PRASANNA - US Department Of Agriculture (USDA); BAATH, GURJINDER - Oklahoma State University; PRASAD, VARA - Kansas State University

Submitted to: Journal of Agriculture and Food Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/20/2023
Publication Date: 12/24/2023
Citation: Singh, H., Northup, B.K., Gowda, P., Baath, G.S., Prasad, V.P. 2023. Moth bean and tepary bean as green nitrogen sources in intensive winter wheat cropping systems. Journal of Agriculture and Food Research. 15. Article 100938. https://doi.org/10.1016/j.jafr.2023.100938.
DOI: https://doi.org/10.1016/j.jafr.2023.100938

Interpretive Summary: Winter wheat is an important part of agriculture in the U.S. southern Great Plains (SGP), with roughly 16 million acres planted yearly to produce grain, hay, and grazing. Most wheat in the SGP is grown in continuous rotations without irrigation, with crops separated by periods of summer fallow to conserve moisture for the next wheat crop. However, the wheat-summer fallow system has issues that affect its performance, including poor water storage, use of applied nitrogen (N), and soil erosion. Growing green N crops during summers may help to offset some of the factors affecting wheat-summer fallow systems. Green N crops can protect soils from erosion, provide N for wheat, and increase water use in growing crops rather than allowing losses through evaporation from bare soil. We compared the responses of winter wheat to two drought-tolerant grain legumes from different parts of the world (tepary bean from northern Mexico and the US Desert Southwest; and moth bean from India) to soybean (a check crop for green N supply), and summer fallow with no N applied as a control. During 2019 to 2020, we measured the amount of biomass produced and N supplied by the three legumes, how they impacted soil water, soil nitrogen, yield of winter wheat, and the amount of N transferred from the green N legumes to wheat. We found the green N crops produced similar amounts of biomass, and that soybean provided 22% and 40% more N than tepary bean and moth bean, respectively. All green N treatments reduced available soil water by similar amounts, and increased N content of soils, compared to summer fallow, but only at planting of wheat. Grain yields of winter wheat were greater in response to tepary bean than soybean or the control, while moth bean supported grain yields that were intermediate between tepary bean and soybean. Though, soybean provides greater amounts of N, the recovery of N in wheat biomass was higher under the moth bean and tepary bean treatments. Therefore, both moth bean and tepary bean are capable of serving as green sources of N for winter wheat in the US SGP. Further research is needed to define how planting dates and lengths of growing periods applied to the green N crops affects soil water available for wheat, and yields produced by winter wheat. Such information will provide an improved understanding of the potential of such novel crops to perform as green N crops.

Technical Abstract: Replacing summer fallow with cover or green N crops could help mitigate economic and environmental problems and increase resilience of agroecosystems in the United States (US) Southern Great Plains (SGP). Drought tolerant legumes could be appropriate choices, as they can provide both cover and serve as green source of nitrogen (N) for winter wheat. This 2-year experiment (2019-2020) evaluated the potential of two summer-grown grain legumes [tepary bean (Phaseolus acutifolius) and moth bean (Vigna aconitifolia)] as green sources of N in comparison to soybean (Glycine max). Biomass production by legumes, their impacts on soil water, soil nitrogen, yield of winter wheat, and N transfer from green N biomass to wheat were measured. Biomass production by the different green N crops was not different, and soybean provided 22% and 40% more N than tepary bean and moth bean, respectively. Soil water was reduced under all green N treatments compared to 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 greater under tepary bean than the soybean or control treatments, while yield responses to moth bean were intermediate to tepary bean and the other treatments. Though, soybean provided greater amounts of N than moth bean and tepary bean, N recovery in wheat biomass was greater under moth bean and tepary bean. Therefore, it can be concluded that both moth bean and tepary bean can serve as green sources of N for winter wheat in the US SGP. Future research on effects of planting dates and lengths of growing period on soil water and subsequent yields by winter wheat will improve the understanding for the potential of such novel crops as summer-grown green N.