Oat green manure improves soil health indicators and lentil yield with GHG trade‐offs under rainfed semiarid conditions

Green manuring may improve soil properties, but its effects on crop productivity and greenhouse gas (GHG) emissions remain poorly understood in rainfed semiarid systems. This study evaluated oat (Avena sativa L.) as green manure on soil properties, GHG emissions, and lentil (Lens culinaris Medik.) yield in a rainfed semiarid cropping system in western Iran. A field experiment was conducted in 2021 and 2022 evaluating four oat biomass incorporation rates (0, 2, 4, and 8 Mg of dry weight ha−1). A randomized complete block design with four replications was employed. Oat biomass was incorporated prior to lentil sowing to a depth of 30 cm. Soil CO2 and N2O fluxes were measured during lentil cultivation, while lentil yield, N uptake, and soil chemical properties were evaluated at harvesting. Regression analysis showed that soil organic carbon and total nitrogen increased linearly with oat biomass incorporation rate, while available water, aggregate stability, and grain yield showed quadratic responses, indicating improved soil functioning and crop productivity but with marginal gains at higher biomass rates. Lentil N uptake increased linearly with increasing oat biomass incorporation, confirming improved nutrient acquisition. Soil CO2 and N2O emissions also increased with higher biomass inputs, although their responses varied between growing seasons. The principal component analysis indicated increasing oat biomass incorporation was associated with improvements in soil fertility and lentil performance, but also with greater GHG emissions. Overall, oat green manure improved soil fertility and lentil productivity under semiarid rainfed conditions, but residue management should be optimized to balance agronomic benefits with GHG trade-offs.