Long-Term Winter Cover Crops Alter the Soil Microbial Biomass and Enzyme Activities in Brazilian Oxisols

The diversification of cover crops grown in soils with granulometric variability may potentially enhance microbial community and enzyme activities. Thus, the main goal was to evaluate the effect of autumn/winter cover crop sequences and cash crops in spring/summer on soil microbial biomass and enzyme activities. The experiment was conducted in open-field microplots (10 m × 1 m × 0.7 m), containing soils from B horizon of five Oxisols with granulometric variability and clay content ranging from 17 to 80 dag kg−1. The treatments were three cover crops and a winter fallow with a completely randomized experimental design with three replicates. Soil samples from the 0–10 cm layer were collected to analyze soil microbial biomass of carbon and nitrogen, enzyme activities of the acid phosphatase, arylsulfatase, urease, and fluorescein diacetate hydrolysis. The number of nodules in soybean roots was average 63 ± 14.42 nodules per plant and dry mass of nodules was 169 ± 13.74 mg plant−1. Soybean nodulation and N uptake ensured the supply of nitrogen to the soybean plants with 331 ± 82 mg plant−1. Overall, diversified autumn/winter cover crop sequences provide plant residue, containing nutrients, and different carbon/nitrogen, which alters microbial biomass, the ratio of Cmic/Nmic, basal respiration, and soil enzyme activities within each Oxisol with different particle size distribution.