Soil Microbial and Chemical Properties of a Minimum and Conventionally Tilled Wheat–Fallow System

Abstract

© Soil Science Society of America. Tillage alters the soil environment and microbial communities responsible for decomposition and nutrient cycling. This study aimed to evaluate the effects of tillage intensity (minimum vs. conventional) on the soil chemical and microbial properties of a winter wheat (Triticum aestivum L.)-fallow rotation in the low-precipitation zone of the Pacific Northwest. Soils collected for 2 yr at two depths from both crop phases (wheat and fallow) were analyzed for pH, nutrient availability, total C and N, fungal and bacterial gene abundance, and enzyme activity related to C, P, and N cycling. All soil variables excluding soil pH were significantly greater in the top 10 cm of the soil. Except for pH and nitrate, all were greater in 2016 than in 2017. Across the full rotation, tillage did not affect any measured parameter. Instead, crop phase influenced several soil chemical properties and arylamidase activity, although the effects were not consistent across depth. Fungal abundance was influenced by tillage intensity but only in the top depth under wheat, indicating a phase-specific effect rather than a change persisting across the entire rotation. Soil enzymes were strongly related to total C, total N, and phosphate across the two soil depths, but effects were inconsistent between depths and across phases. Overall, crop phase and year were stronger drivers of soil chemical and microbial properties than tillage intensity. Short-term (<4 yr) tillage intensification does not have a strong influence on the nutrient cycling capacity of soil, although fungal numbers may decline in the cropped phase.