Unraveling the Yield-Soil Amelioration Nexus in Alkaline Soils: Agronomic Performance and Soil Chemical Responses of Green Manure Crops

Abstract

Although green manure crops are widely recognized for ameliorating alkaline soils, some previous studies have focused mainly on laboratory germination screenings or single yield indicators, and field validation of the synergy between high yield and soil improvement remains comparatively limited. This study evaluated 16 species/accessions with varying salt tolerance in a typical alkaline soil (initial pH 9.01, EC 306 μS·cm−1) in Heilongjiang Province during 2024–2025, based on prior laboratory screening. The experiment was conducted at a single location with three field replicates, and the same plots were monitored across both years. Plant height, fresh/dry grass yield, and soil properties (pH, EC, organic matter, nutrients) were monitored. Glycine max (L.) Merr. and Sesbania Scop. achieved dual synergy, with two-year average fresh yields of 40,733 and 35,750 kg·ha−1, respectively, while reducing soil pH by 0.28–0.29 and electrical conductivity (EC) by 42.2–46.3%. Melilotus officinalis and Vicia villosa Roth exhibited the strongest alkali reduction (pH ↓0.29, EC ↓39.0–39.7%) with moderate yields. Sorghum sudanense showed the highest salt reduction (EC ↓49.0%). Principal component analysis classified the 16 species into four functional types, revealing preliminary ecological patterns for functional differentiation. This study proposes a “laboratory screening–field validation–functional classification” evaluation framework, which requires further validation across different regions and longer time scales for the biological amelioration of alkaline soils.