Integrated application of green manure and mushroom residue improves soil quality and carbon-nitrogen fraction, and pepper yield and quality

Greenhouse vegetable systems face degradation from intensive inputs and weak organic matter recycling. The synergistic effect of combining green manure and mushroom residue on soil fertility, especially regarding soil carbon-nitrogen fractions, and yield-quality characteristic is poorly understood. This study investigate the impacts of green manure and mushroom residue on soil quality and pepper yield and quality. A randomized block design with five treatments, including CK (control), GM (green manure 3000 kg ha - ¹), MR (mushroom residue 7500 kg ha - ¹), GMS (green manure 3000 kg ha - ¹ and mushroom residue 3750 kg ha - ¹), and GMMR (green manure 3000 kg ha - ¹ and mushroom residue 7500 kg ha -1 ). The GM, MR, GMS and GMMR significantly improved the contents of total nitrogen (TN), total phosphorus (TP), total potassium (TK), alkaline hydrolyzable nitrogen (AN), available phosphorus (AP), available potassium (AK), ammonium nitrogen (NH 4 + -N), nitrate nitrogen (NO 3 - -N), and soil organic carbon (SOC), dissolved organic carbon (DOC), dissolved organic nitrogen (DON), soil inorganic nitrogen (SIN), microbial biomass carbon (MBC), easily oxidizable organic carbon (EOC) compared to CK treatments with the order GMMR > GMS > MR > GM > CK in both soil layers. The SOC storage in the GMMR, GMS, MR and GM treatment in the 0-10 cm increased by 24.25%, 24.49%, 17.56% and 4.39% compared with CK, which increased by 54.28%, 31.55%,25.31% and 9.46% compared with the CK treatment in 10-20 cm layers, respectively. The SOC storage and carbon sequestration efficiency under different treatments followed the order: GMMR > GMS > MR > GM. Compared to CK, the GMMR and GMS treatment achieved the highest pepper yield of 48797 and 46708 kg ha -1 , representing a significant increase of 17.55% and 12.52%. The random forest model showed MBC is key soil factors affecting yield and soluble sugar, and NO 3 + -N is key soil factors affecting soluble protein. The GMMR treatment emerges as the optimal organic amendment strategy for similar greenhouse conditions in semi-arid regions.