Evaluating the effects of moisture variability and simulated exudate inputs on nitrogen availability in contrasting tillage systems

Nutrient losses in soils are associated with the long-term degradation of soil health and can be attributed to inadequate management practices or worsened by climate change. Semi-arid regions experience varying environmental conditions, such as fluctuation in rainfall and drought events, which can contribute to soil nitrogen (N) losses. However, N losses can be mitigated through conservation management, such as conversion to no-till (NT) and promoting plant root inputs, which can enhance nutrient cycling and potentially improve climate resilience compared to conventional tillage (CT). To address these knowledge gaps in nutrient management and N losses, we conducted lab incubations under controlled environmental conditions using soils from contrasting tillage systems. The primary objectives of the research were to (1) evaluate how N dynamics are affected by simulated root exudates in no-till and conventional tillage systems, (2) explore how fluctuating moisture conditions affect N dynamics in no-till and conventional tillage systems, and (3) determine how N dynamics are affected by the combination of exudates and moisture content in soils. During an eight-day incubation, we simulated moisture fluctuations and root exudate inputs. In these experiments, exudate treatments included oxalic acid, glucose, and water, and moisture treatments included soils undergoing a wet-dry cycle or held at constant moisture. Samples were collected post-harvest in May 2023 and during the fallow period in August 2023 across various locations in Oklahoma. The combination of root exudates and moisture had variable effects on N dynamics across the different management systems. N mineralization rates and microbial biomass N were elevated under wet-dry cycling compared to the constant moisture treatment. This suggests that alternating periods of drought and moisture could accelerate N mineralization and potentially create more opportunities for N loss. In general, we observed a greater sensitivity of N measurements to the simulated moisture fluctuations than to the contrasting tillage treatments. Simulating wet-dry cycles and effects on microbial processes may be a sensitive soil health indicator that warrants further investigation.