Effects of Liquid Microbial Fertilizer on Tomato Yield, Fruit Chemical Quality, and Rhizosphere Soil Quality in Acidified Phosphorus-Enriched Greenhouse Soil

Continuous intensive fertilization in greenhouse vegetable production can cause soil acidification, salinity, and phosphorus (P) enrichment, yet direct comparisons between microbial and chemical fertilizers under equivalent nutrient inputs remain limited. We hypothesized that liquid microbial fertilizer (LM) would improve soil functions more effectively than chemical fertilizer (CF) and that reduced LM input could maintain tomato productivity. A fixed-site greenhouse experiment was conducted in 2025 at the Acheng Experimental Base of Northeast Agricultural University, Harbin, China, as the third year of a trial established in 2023. A randomized complete block design with four blocks was used, comprising seven treatments with four independent replicate plots per treatment: an unfertilized control (CK) and LM and CF applied at 50%, 75%, and 100% of the conventional N–P2O5–K2O rate. Soil chemical properties, enzyme activities, aggregate stability, soil quality, tomato yield, and fruit quality were evaluated. Compared with CF at matched nutrient inputs, LM alleviated soil acidity and salinity, enhanced C and N retention, enzyme activities, and aggregate stability. The soil quality index (SQI) was 27.80%, 56.62%, and 99.30% higher under LM1, LM2, and LM3 than under the corresponding CF1, CF2, and CF3 treatments, respectively. LM1 and LM2 increased tomato yield by 46.20% and 39.40% relative to CK, whereas LM3 favored fruit and soil quality. Overall, reduced LM application effectively balanced tomato productivity, fertilizer-input reduction, and soil improvement in acidified, P-enriched greenhouse soil.