Biological nitrogen fixation of cool‐season legumes in agronomic systems of the Southern Great Plains

Abstract

AbstractBiological nitrogen fixation (BNF) is a key ecosystem service rendered by legumes, but quantitative information is lacking regarding BNF in the Texas Rolling Plains (TRP), an easterly portion of U.S. Southern Great Plains where cool‐season legumes can typically be grown as cash or cover crops in dryland conditions. Using three diverse cropping systems studies (Site 1, long‐term cotton [Gossypium hirsutum L.]‐cover crop systems; Site 2, short‐term cotton‐cover crop systems; and Site 3, transitional organic wheat [Triticum aestivum L.] system), our research objective was to quantify and compare BNF and associated parameters among four cool‐season legumes (Austrian winter pea [Pisum sativum subsp. Arvense], hairy vetch [Vicia villosa], crimson clover [Trifolium incarnatum], and lentil [Lens culinaris]) in different settings. At Sites 1 and 2, winter pea had growth of 2.73 to 3.44 Mg ha−1, the greatest percent N derived from the atmosphere (%Ndfa; 57.2–72.6%) and, depending on site, the greatest level of BNF (67–74 kg N ha−1). Results from the organic system (Site 3) demonstrated winter pea was also productive in growth and BNF when intercropped with wheat in N‐poor soil, with exceptionally high %Ndfa (92.7%). Hairy vetch and lentil differed in growth and %Ndfa, but had comparable BNF (46–51 kg N ha−1) at Sites 1 and 2. Growth of crimson clover was poor. This data provides insights on how cool‐season legumes differ in BNF in the TRP in a year when legume growth was average for the region. The TRP has a volatile climate, however, indicating further study is needed to fully understand the BNF benefit cool‐season legumes can provide in the region.