Straw Retention Enables the Yield and Quality Benefits of Reduced Tillage in Winter Wheat and Spring Barley: A Long-Term Study

Agronomic practices can modify cereal grain chemical composition and processing performance. Long-term evidence linking agricultural management with functionality-related quality remains limited, especially in terms of combined tillage x crop residue management strategy. We evaluated the effects of long-term tillage simplifications and straw management on productivity and processing-relevant traits of winter wheat and spring barley in a split-plot field experiment (Lithuania). Straw was either removed (S0) or chopped and retained (S1), and six tillage systems were compared (conventional ploughing (CP), shallow ploughing (SP), shallow cultivation (SOW), stubble over winter, no-till with cover crops (NTC), and no-till without cover crops (NT)). The yield and starch content of winter wheat and spring barley groats increased with the addition of straw and the application of SOW, NTC, and NT systems. The hectolitre mass of winter wheat and spring barley grains increased with the addition and removal of straw using SP technology. The protein content and wet gluten content of winter wheat and spring barley grains decreased, while the starch content increased, with the addition and removal of straw using SC technology. In wheat, protein content showed weak separation among treatments, while wet gluten and Zeleny sedimentation displayed mostly directional trends (wet gluten–sedimentation correlation: r = 0.844 under S0 and r = 0.984 under S1). In terms of the tillage systems, it can be stated that in most cases, SP and NT increased grain yield and improved quality indicators, while SC and NTC technologies showed opposite results. Soil-function assessment (CEI, 10–25 cm) indicated substantially higher integrated soil functioning under conservation agriculture (e.g., SOW/NTC/NT: 5.28–5.70) than under conventional systems (CP: 3.23). The results support framing sustainable soil management for cereal functionality as a system package: residue retention enables the productivity benefits of reduced-tillage systems while maintaining key quality proxies.