There is a lack of studies that have investigated grain yield, its components and photosynthesis in late stages of wheat growth, giving us insufficient understanding of how these factors interact to contribute to yield during this period. As a result, three field experiments were carried out examining 20 winter wheat genotypes of diverse origins under irrigated, terminal drought and dryland conditions in the southern Idaho. Our objective was to evaluate the interaction between post‐anthesis physiological traits, especially leaf‐level photosynthetic capacity, senescence and yield components on grain yield in different moisture regimes. Genotype differences were found in leaf‐level photosynthesis and senescence, canopy temperature depression, grain yield and yield components in each water regime. Grain yield was closely associated with traits related to grain numbers. In all three moisture regimes, positive correlations were observed between grain yield and photosynthesis that were dependent on the timing or physiological growth stage of the photosynthetic measurement: highly significant correlations were found in the mid‐ and late grain filling stages, but no correlations at anthesis. Consistent with these findings, flag leaf senescence at the late grain filling stage was negatively correlated with grain yield and photosynthetic rate (under terminal drought and dryland conditions). These findings provided evidence that grain yield was sink‐limited until the final stages of growth, at which time sustained photosynthesis and delayed senescence were critical in filling grain. Because the trends were consistent in moisture sufficient and deficient conditions, the results suggest that late‐season photosynthesis and delayed leaf senescence are driven by the size of the reproductive carbon sink, which was largely governed by factors affecting grain numbers.

Cover cropping in the fallow phase of winter wheat (Triticum aestivum L.)–fallow systems of the semiarid Pacific Northwest has been identified as an opportunity to build resilience and enhance farm profitability. Nine fall‐ and spring‐sown cover crops (CCs) grown during the traditional fallow period were evaluated at sites in the low and intermediate precipitation zones of the region in a 2‐year study (2021 and 2022). The fall‐sown CCs included winter pea (Pisum sativum L.), winter lentil (Lens culinaris Medik.), and fall species mix; and the spring‐sown CCs included common vetch, yellow mustard, lacy phacelia, tillage radish (Raphanus sativus L.), spring barley (Hordeum vulgare L.), and a spring species mix. CCs were evaluated for biomass production and impacts on soil water and weeds. CC growth was dependent on location, year, planting timing, and CC species. Fall‐sown CCs generally produced more biomass than spring‐sown CCs across site‐years, with winter peas and the fall species mix being most productive. Following a year of greater than average precipitation, no negative effects of CCs on fall soil moisture were observed at the intermediate precipitation site, while fall‐sown CCs reduced soil moisture at the low precipitation site. The suppressive effect of CCs on weeds ranged from null to moderate, depending on site, year, and CC seeding time. Fall‐sown CCs more consistently suppressed weeds than spring‐sown CCs. Additionally, fall‐sown CCs were terminated in the spring before weeds set viable seeds, saving a herbicide application and reducing herbicide pressure without exacerbating future weed issues. Overall, select fall‐sown CCs showed promise to enhance ecosystem services during the traditional fallow period.

Biological 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.