Effects of biogas slurry application on peanut yield, soil nutrients, carbon storage, and microbial activity in an Ultisol soil in southern China

Biogas slurry (BS) was known to influence soil-plant ecosystems when applied as a fertilizer, especially in combination with a chemical fertilizer (CF). Limited information was available regarding how this combination of BS-CF actually affected the soil-plant ecosystems. The purpose of this study was to evaluate the effects of BS-CF combinations on peanut yield, soil properties, and carbon (C) storage in a red soil (Ultisol) in southern China. The soil was fertilized with five treatments, including a control (T1), CF-only (T2) treatment, and three treatments with different BS-CF combinations (T3-T5). The final quantities of N/P2O5/K2O applied in T2-T5 were 120:90:135 kg ha(-1). In T3-T5, 15 % (18 kg ha(-1)), 30 % (36 kg ha(-1)), and 45 % (54 kg ha(-1)) of total N (TN), respectively, were applied with BS and the remaining TN was applied with CF. Crop yield, soil nutrients, C storage, and microbial activity were determined through field and laboratory experiments. In the field experiment, peanut grain yields of T3-T5 were higher than those of T1 (44.5-55.7 %) and T2 (10.8-19.4 %), with the highest yield from T4 (3588 kg ha(-1)). The relationship between BS-TN inputs and peanut grain yield conformed to the linear-quadratic equation: y = -1.14x (2) + 59.1x + 2988 (R (2) = 0.98). The biomasses of peanut plants, at the flowering, pod production, and harvesting stages, were higher in T4 compared with those in T1 and T2. Moreover, T4 produced higher soil N and P (total and available) concentrations at the pod production and harvesting stages relative to other treatments, with increased soil microbial biomass C and N, and enhanced dehydrogenase and urease activities, at the flowering, pod production, and harvesting stages. Data from the incubation experiment were fitted to a first-order kinetic model, which showed that although the application of BS increased potentially mineralizable C, the additional C seemed to slowly degrade, and so would be retained in the soil for a longer period. A BS-CF combination increased peanut grain yield and biomass, due to increases in soil N and P availability, microbial biomass C and N concentrations, and urease and dehydrogenase activities. Moreover, the organic C retention time in the red soil was extended. Combined application of BS-CF at a suitable ratio (36 kg BS-TN ha(-1)), together with proper management practices, could be effective to improve the quality and nutrient balance of amended soils.