Temporal Changes in Soil Microbial Properties in Claypan Soils.

The temporal change in soil microbial properties with crop rotation is poorly characterized in claypan soils. The objective of the research is to assess how claypan soils and tillage mediate changes in soil microbial properties with time in the predominant corn/winter wheat/soybean rotation system of the Central Great Plains. Soil microbial communities were examined through both PLFA analysis and 16S rRNA gene sequencing on an Illumina MiSeq system. Hydrolase and oxidase activities were also measured in this study. Soil physical and chemical properties including pH, moisture content, texture, and soil nutrients were examined. Crop yields were compared with soil properties. We found that soil pH was lower as corn growing and then increased in one pH degree as soybean growing. Both hydrolase and oxidase activities and population were lower as soybean growing. Carbon and nitrogen-required enzyme activity were greater at wheat planting and following dormant phase. Fungi population was higher in winter. Although soil water content significantly declined in summer, microbial activity and biomass did not change simultaneously. Tillage reduced microbial activity and microbial biomass on average but the changes were only in top 5 cm. While both fungi and bacteria were abundant in the no-till system, the fungal to bacterial ratio was similar in no-till and tillage systems. Specific hydrolase activity per microbial biomass did not change with crop growing phases or seasons. The interaction between crops and abiotic factors together with tillage effects determined the microbial biomass and activity in claypan soils.