Biomass maturity as a key driver of green manure decomposition and soil nutrient dynamics

Abstract

Green manuring plays a vital role in enhancing soil fertility and organic matter dynamics in sustainable cropping systems, yet its effectiveness largely depends on the biochemical quality and maturity of the incorporated biomass. To elucidate the influence of crop type and developmental stage of buried plant biomass on soil traits, a 17-week pot experiment was conducted using safflower (Carthamus tinctorius), radish (Raphanus sativus), and white mustard (Sinapis alba) plants, harvested at two maturity stages: after 11 weeks (biomass A) and 12.5 weeks (biomass B) of cultivation. Biomass maturity exerted a stronger influence than crop identity on plant composition (fat, NDF, cellulose, hemicellulose), amount of residual plant biomass, and on soil properties (β-glucosidase, urease, pH). The more matured biomass (B) contained higher carbohydrates and fat contents, and despite higher recalcitrance indices, it decomposed more completely, resulting in lower residue retention. Crop-specific responses of soil traits were the most distinct at the early harvest stage: radish biomass A enhanced soil enzyme activities and total N, whereas white mustard, particularly biomass B, promoted soil P, Mg, and K availability alongside elevated N-acetyl-β-D-glucosaminidase activity. Safflower decomposed more slowly, indicating potential for longer-term carbon stabilization but limited immediate fertility gains. Overall, harvest timing emerged as a critical determinant in tailoring green manures for both nutrient cycling efficiency and soil carbon stabilization.