Predicting soil nitrogen dynamics after incorporating cereal cover crop residues

Abstract Recently adopted regulations for water resource protection on California’s Central Coast incentivize cover-cropping, creating a need for simple, reliable tools that determine soil nitrogen (N) dynamics after the incorporation of cover crop residues. Three microcosm experiments were conducted using common winter cover crop shoot residues (‘Pacheco’ triticale and ‘Merced’ rye) with carbon to N (C:N) ratios ranging from 9.1 to 42.9 to determine the impacts of residue C:N ratio and temperature on net N mineralization and immobilization rates over time, as well as the impact of temperature on gross N turnover rate. Residue C:N ratio was found to be inversely correlated with N mineralization, while temperature was found to be positively correlated with N mineralization. This data was further utilized to model N dynamics of cover crops terminated at different growth stages, revealing the best predictor of N turnover to be residue biomass and C:N ratio, rather than a residue’s cell wall components (lignin, cellulose, hemi-cellulose). Our results indicate that few inputs are required to reliably simulate N release from incorporated cereal cover crop residue, providing a framework for the creation of future support tools that will guide Central Coast vegetable growers in their fertilization decisions in fields following cover crops. While the examples presented in this paper focus on intensive vegetable production on California’s Central Coast, the information is highly relevant for any cropping system with cereal cover crops.