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

Abstract

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.