Biochar and Cow Manure on Chemical and Microbial Community in Regosol with Bean

Abstract

The effects of coffee biochar residue combined with cow manure fertilizer on soil chemical attributes, microbial biomass, and structure and abundance of the soil microbial community are not fully understood. Thus, the objective of this study was to evaluate the effect of coffee biochar combined with cow manure on chemical and microbial attributes in soil cultivated with bean (Phaseolus vulgaris). We hypothesized that biochar from coffee residues drives the bacteria, fungi, and diazotrophic communities in a sandy soil and increases the abundance of these microorganism groups, raising soil basal respiration and microbial biomass. The experiment was carried out in a completely randomized design and was distributed in a factorial scheme (2 × 3 + 2) including two types of biochar (coffee ground-CG and coffee husk-CH) at three dosages (4, 8, and 16 t ha−1), and two control groups (S = native soil without treatment (−control) and E = fertilization with cow manure at dosage of 15 m3 ha−1 (+control)). The experiments were conducted with four repetitions. All treatments received the same dosage of cow manure applied in sandy soil and bean seeds were grown in pots. Soil samples were collected after 45 days to evaluate chemical attributes, total organic carbon (TOC), microbial biomass (C, N, and P), soil basal respiration, structure and abundance of total bacterial and fungal community (16S rRNA, 18S rRNA) and diazotrophs (nifH) in the soil by DGGE (denaturing gradient gel electrophoresis) and qPCR (real-time quantitative PCR), respectively. The results showed that TOC increased 9 and 11.5% with highest dosage of CG and CH biochar, respectively; thus, CG at 4 t ha−1 increased the C:N ratio in soil (4.7 times). The addition of biochar combined with cow manure increased soil basal respiration in CG at 16 t ha−1. The combined application of CH at 16 t ha−1 and cow manure increased the P content (2.37 times) and K+ (5.6 times). The highest increase in C from microbial biomass was found in CG at 16 t ha−1 and the addition of biochar and cow manure did not affect the P content in microbial biomass; nevertheless, biochar increased the nifH gene abundance by 8.23% at 16 t ha−1. Biochar addition influenced the structure of soil microbial communities, presenting distinct and well-differentiated communities in the multivariate analysis, according to the dosage and type of biochar. The group formed by different CG dosages showed a higher number of 16S genes, and greater amounts of Nmic, nifH, soil basal respiration, metabolic quotient, K, and Na. The major conclusion of this study was that coffee biochar, used in combination with cow manure, significantly improves the chemical and microbiological attributes of sandy soil cultivated with bean.