Straw Return Improves the Environment of Saline–Alkali Soil: A Meta-Analysis

The relative effects of the different straw return types on saline–alkali soils remain unclear. We hypothesized that the five return types distinguished in practice (two amounts: moderate and total return; three placements: mulching, rotary tillage and ploughing) differ in their effect on the physical (H1) and chemical (H2) properties, so that the practice most suitable for a given soil and crop can be identified. Publications from 1990 to 2024 in the China National Knowledge Infrastructure and Web of Science yielded 503 field studies and 548 paired data sets, pooled with a random-effects model. Total straw return reduced bulk density and increased porosity and water content more than moderate return. Ploughing return was most effective for bulk density, porosity, water content, soil organic carbon and available phosphorus; mulching return for organic matter, available nitrogen and available potassium; and rotary tillage return for total nitrogen. Biochar addition decreased fungal Shannon and Simpson indices but increased Chao1 and ACE richness; decomposition agents accelerated decomposition and raised enzyme activities. We conclude that no single return type is optimal for all properties, so the type should be matched to the target soil property, while limited replication and the heterogeneity of the source studies constrain generalization.