Temporal Variation of Soil Microbial Properties in a Corn–Wheat–Soybean System

Abstract

Soil microbial properties vary temporally with crop development and species, but this change is poorly characterized. Our objective was to assess how tillage and crop development mediate changes in soil microbial properties in a corn–winter wheat–soybean system. We evaluated microbial activity through extracellular enzyme activities, microbial communities through phospholipid fatty acid profile, and soil physicochemical properties (including water content, pH, and soil nutrients) at different crop stages. Tillage reduced microbial activity and microbial biomass but only in the upper 5 cm. Hydrolase activities and microbial biomass exhibited temporal variation with crop growth, but measured microbial properties were unresponsive to tillage or fertilizer events. Wheat resulted in higher active C and soil organic matter quality than corn, as indicated by β‐glucosidase/oxidase activity ratio. Greater substrate availability after corn harvest stimulated the production of enzymes and higher bacterial and fungal biomass to decompose the recalcitrant C. The microbial lipid community was different in soybean than in either corn or wheat. These results suggest that, in addition to tillage, crop type was an important driver of change in soil microbial properties. Wheat resulted in higher soil hydrolase activity and microbial biomass than corn. The lack of residue from the preceding crop may explain the lower microbial biomass and activity during corn growth. Incorporating wheat in the crop rotation may provide rhizosphere C inputs that support greater microbial activity. Significant temporal variation in soil microbial properties indicates the need to consider time of soil sampling to better capture the variability of soil health assessments.