Unveiling the Impacts of Biochar, Manure and Their Optimal Combinations on Microbiological Soil Health Indicators and Lettuce Biomass

Continuous use of chemical fertilizers has deteriorated soil health and crop productivity. Replenishing soil nutrients and microbial activity with eco-friendly soil amendments such as biochar and manure is therefore necessary to sustain soil health for crop production. However, studies are limited regarding the evaluation of biochar and poultry manure effects on soil health, attributed mainly to microbial extracellular enzymes and respiration. Therefore, the present study was designed to investigate the effects of poultry manure and biochar on soil physico-chemical and microbiological properties and lettuce biomass accumulation in a pot experiment. The pots were amended with poultry manure either alone and or in combination with low (10%) and high (20%) rates of biochar. The treatments included were; (i) control, (ii) manure alone (M), (iii) manure plus 10% biochar (M + B10, and (iv) manure plus 20% biochar (M + B20). Results revealed that soil extracellular enzymes related to C, N, and P mineralization, soil basal (BR), and substrate induced respirations (SIR) were significantly affected by applied manure and manure-biochar. However, there were large differences observed for applied amendments regarding various soil and crop parameters. Specifically, the manure combined with a high rate of biochar (M + B20) enhanced total carbon (TC) content, dehydrogenase activity (DHA), BR, and all SIRs except Arginine-IR. On the other hand, manure combined with a low rate of biochar (M + B10) resulted in enhanced lettuce aboveground dry biomass (AGB-dry). The manure treatment alone (M), however, proved to be the most influential treatment in improving soil enzymes (beta-glucosidase, N-acetyl-beta-D-glucosaminidase and phosphatase) involved in C, N, and P mineralization compared to the other treatments and control. Thus, it was concluded that the sole application of M and M + B20 improved both fertility and soil health, which therefore could be a promising direction for the future to enhance soil quality and crop productivity.