Quantification of soil microorganisms under several cover crops managed with no-tillage system for fifteen years in the Brazilian Cerrado

Abstract

The natural heterogeneity of soil sustains a dynamic balance between environmental conditions and the residents of the microbiota. In this context, the objective of our work was to identify and quantify distinct groups of microorganisms in winter (2014) and summer (2015), in an Oxisol cultivated for fifteen years with no-tillage system in the Cerrado biome. The experimental design was randomized blocks in a factorial scheme (3x3) with three cover crops (brachiaria, millet and crotalaria) evaluated at three depths (0-0.05, 0.05-0.1 and 0.1-0.2 m), with four replications in both seasons (winter and summer),. Endospore-forming bacteria, actinomycetes, yeasts, phosphate solubilizing microorganisms and cellulolytic microorganisms were evaluated. Among the studied cover crops, millet presented superior populations of endospore-forming bacteria in winter, and actinomycetes in summer. The populations of other microorganisms were not different among cover crops in the same season. The population of phosphate solubilizing microorganisms did not differ between seasons, indicating that these microorganisms are less vulnerable to seasonal variations in no-tillage system. In winter, smaller populations of endospore-forming bacteria, yeasts, and actinomycetes were observed with increasing depth in the soil. In summer only the population of endospore-forming bacteria decreased with soil depth. Soil depth did not affect the population of cellulolytic microorganisms under on-tillage system. Our findings suggest that millet is the best fallow cover crop for no-tillage system.