Abstract Nitrogen (N) supply from cover crops to subsequent crop primarily depends on cover crop biomass production. Questions remain on how cover crop biomass interacts with abiotic factors to affect soil inorganic N and when N availability is highest following cover crop termination. This study identified key variables influencing N mineralization dynamics in cover crop systems, including air temperature, precipitation, gravimetric water content, cover crop biomass, weed biomass, and days after cover crop termination (DAT). Using random forest modeling with leave‐one‐year‐out cross‐validation, we analyzed 30 years (1990–2020) of bi‐weekly soil N measurements in two corn ( Zea mays L.)‐soybean ( Glycine max )‐wheat ( Triticum aestivum L.) rotations with a legume cover crop ( Trifolium pratense L.) to identify key drivers of soil inorganic N release. Models explained 35% of variability in soil NO 3 − ‐N and 15%–32% variability in soil NH 4 + ‐N in the two systems. Variable importance analysis revealed that DAT was the most important driver affecting soil inorganic N availability, with air temperature as a close second. Partial dependence plots showed that soil NO 3 − ‐N increased rapidly following cover crop termination and peaked at approximately 50 DAT. Two‐dimensional partial dependence plots revealed interactions among DAT, temperature, and cover crop biomass in affecting soil NO 3 − ‐N. Temperature >12°C and cover crop biomass above 4000 kg ha −1 were associated with high soil NO 3 − ‐N levels. There were productivity differences between the management systems studied, yet both systems showed similar N dynamics, suggesting this approach was robust for understanding underlying drivers concerning N mineralization.
KC et al. (Sun,) studied this question.