Assessing the root and shoot composition, decomposition, carbon contribution and nitrogen mineralization trends of single species and mixed cover crops

Context

Annual cover crops (CC) planted in the fall can enhance nutrient cycling in no-till vegetable cropping systems by recycling nutrients to succeeding crops and improving long-term soil health. However, our knowledge of the decomposition dynamics and nutrient release of both aboveground and belowground portions of CC in no-till systems remains limited.

Objective

This study aimed to quantify the fall biomass, nitrogen (N) and carbon (C) accumulation, and spring decomposition and nutrient release of the roots and aerial parts of three common CC species, oat (Avena sativa), field pea (Pisum sativum) (FP), daikon radish (Raphanus sativus) (DR) and their mixture. The goal was to assess the potential nutrient contributions from fall-planted CC to spring-planted successor crops in a no-till system. Additionally, we sought to characterize the relationship between the quality of root and aerial litter and various decomposition parameters.

Methods

A replicated field experiment was conducted to evaluate fall CC biomass, nutrient accumulation, and spring decomposition dynamics, which were evaluated using litterbags. A first-order exponential decay model was applied to quantify CC decay rate (k), N release (kn), C release (kc), and the relative rates of C and N release (kc:kn).

Results

Fall-planted CC produce significant amounts of C (787.7 – 1190.4 kg ha⁻¹ C) during their growing period, potentially contributing to SOC accumulation in agricultural systems. The CC species showed varying potentials for N supply to succeeding crops, with FP, DR and CC mixture likely enhancing plant-available N in soils during spring decomposition, while oat likely contributed to net soil N immobilization. Litter quality was a better predictor of aerial decomposition than root decomposition. Initial moisture and hemicellulose content strongly influenced the decomposition and nutrient release rates in aerial residues, but not in root residues.

Conclusions

Our findings indicate that the rates of decomposition for surface and root residues, as well as spring nutrient release, are influenced by CC species used in no-till cropping systems. Moreover, the dynamics of aerial and root decomposition differ, suggesting that roots and shoots of CC should be considered independently in undisturbed vegetable cropping systems.

Implications

These findings enhance our understanding of the role of annual CC in nutrient cycling in no-till agricultural systems, thereby improving our ability to enhance soil health and promote the sustainability of cropping systems.