Organic residue inputs influence soil biological properties in organic farming systems

The objective of this study was to evaluate the effect of organic residue inputs on microbial biomass carbon (MBC), microbial biomass nitrogen (MBN), enzyme activities (FDA and DHA), and soil organic carbon (SOC) in plots in an organic farming system. Soil samples were collected from experimental plots under a randomized block design using organic (ORG) and conventional (CNV) farming systems to grow acerola (Malpighia glaba L.). A native vegetation (NV) site was used as reference. The highest values of SOC (19.9 and 8.7 g kg(-1)), were obtained in ORG sites, at depths of 0-10 and 10-20 cm, respectively, while the lowest values were found in CNV (5.5 and 4.1 g kg(-1)), and NV (9.7 and 4.5 g kg(-1)) sites measured at similar depths. MBC and MBN measurements were both higher in ORG soils with MBC measurements of 308 and 122 mg kg(-1) in ORG and CNV soil respectively, and MBN values of 72 and 47 mg kg(-1) in ORG and CNV soils, respectively. Total enzyme activity was highest in ORG soils with FDA values at 15.2, 6.2, and 8.5 mg kg(-1) in ORG, CNV, and NV soils, respectively. DHA values were 5.7, 2.4, 3.2 mg kg(-1), in ORG, CNV, and NV soils, respectively. However, the specific activity of enzymes did not vary between systems. The results confirm that inputs of organic residues increase the content of organic C, microbial biomass, and total enzyme activity in soils under the organic farming system.