Evaluating the key factors of soil fertility and tomato yield with fresh and aged biogas slurry addition through greenhouse experiment

Biogas slurry has been used as an amendment to increase soil fertility and crop yield. However, different effects of fresh biogas slurry (FBS) and aged biogas slurry (ABS) on soil properties remain unexplored. Effects of different dilutions of FBS and ABS on soil characteristics, such as soil pH, water-soluble salt concentration, electrical conductivity, nutrient content, microorganisms, nematode, and tomato yield, were examined through greenhouse experiments. The principal component analysis (PCA) and path analysis (PA) elucidated soil quality's crucial components with FBS and ABS application. The results indicated that both FBS and ABS treatments increased pH, the concentration of water-soluble salts, electrical conductivity, nutrient content, and bacterial count and decreased the fungi, actinomycete, and nematode counts in the soil. These effects declined with increasing FBS and ABS dilution. Apart from soil nutrient content, at the same dilution, FBS treatment showed more substantial effects on soil properties than ABS treatment. As per the statistical evaluation, FBS treatments improved tomato yield by direct inhibition of fungi and actinomycetes, while ABS treatment improved tomato yield by increasing total nitrogen and available phosphorus. The results revealed that FBS and ABS improved soil quality and tomato yield by influencing distinct soil properties.