Integrated straw return and biostimulant application improve soil nitrogen supply and grain yield-quality synergy in winter wheat under mild saline-alkaline stress

Introduction Saline-alkaline soils pose significant constraints to sustainable wheat production through impaired nutrient cycling and reduced crop productivity. While straw return and biostimulants are recognized management strategies, their combined effects on soil nutrient dynamics and yield-quality relationships remain poorly understood. Methods A two-year field experiment was conducted under mildly saline-alkaline conditions with four treatments: control (CK), straw return (SR), biostimulant foliar application (BS), and integrated straw return with biostimulant (SR+BS). Soil biochemical properties, enzyme activities, crop physiological parameters, yield components, and grain quality were evaluated. Results The SR+BS treatment significantly enhanced soil organic carbon (28.3%) and total nitrogen (19.6%) compared to the control. Soil enzyme activities increased markedly, with sucrase, urease, alkaline phosphatase, and catalase showing increases of 67.9%, 32.1%, 47.6%, and 44.5%, respectively. Soil inorganic nitrogen availability was substantially enhanced, with NH 4 + -N and NO 3 − -N increasing by 47.7% and 39.8%. These improvements were associated with enhanced crop performance: leaf area index and dry matter accumulation increased by 37.5% and 49.1%, respectively. Grain yield reached 8770 kg ha −1 (a 40.8% increase), while grain protein content reached 16.4% (a 25.2% increase), demonstrating improved yield-quality relationships under stress conditions. Discussion These findings indicate that integrated straw return with biostimulant application drives a cascade-like response — from enhanced soil carbon-nitrogen supply through improved physiological processes to increased crop productivity. This integrated strategy offers a promising and sustainable intensification approach for wheat production in saline-alkaline agroecosystems.