Date of Award

2-3-2026

Degree Type

Thesis

Degree Name

Master of Environmental Science (M.Env.Sc.)

Department

Agricultural and Environmental Sciences

First Advisor

Resham Thapa

Abstract

Grass-legume cover crop mixtures are promoted to balance ecosystem services, but predicting their decomposition and nutrient release remains a challenge. A two-year litterbag study investigated the decomposition of cereal rye, crimson clover, their field mixture, and a gradient of biomass proportions in a no-till corn system. Monocultures exhibited a strong functional dichotomy where rye decomposed slowly with a large recalcitrant fraction and clover decomposed rapidly. The field mixture yielded high biomass similar to rye and exhibited intermediate decomposition kinetics. Crucially, analysis of non-additive effects revealed a fundamental decoupling as the residue mass loss showed context-dependent synergistic acceleration but nitrogen release was strictly additive across all mixture proportions and years. This consistent additivity demonstrates that the nitrogen fertilizer replacement value of a rye-clover mixture is a predictable, weighted average of its components. This finding provides a reliable, low-risk framework for forecasting nutrient contributions from cover crop mixtures, enhancing their utility in conservation agriculture.

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