Influence of soil inorganic nitrogen and root diameter size on legume cover crop root decomposition and nitrogen release

Aims: Legume cover crops are primarily grown for their contribution to soil N pools, but the effect that this added N has on cover crop root decomposition and N release is poorly understood. Our primary objective was to determine the effect that soil N and root diameter size have on root decomposition and N release. Methods: We determined coarse (>1-mm diameter) and fine (<1-mm diameter) root distribution for crimson clover (Trifolium incarnatum) and hairy vetch (Vicia villosa Roth) using greenhouse-grown plants, and followed with a 12-week incubation in which coarse and fine roots from both species were incubated under natural and elevated (200 kg ha⁻¹) soil N levels. Results: Crimson clover and hairy vetch consisted primarily of fine roots (≥79 %), which decomposed and released N faster than coarse roots. Soil N addition had a small positive effect on root decomposition, but an inconsistent effect on root N release. There was a net increase in soil inorganic N for all treatments after 12 weeks. Conclusion: These results improved our understanding of decomposition and N release from crimson clover and hairy vetch roots, and are valuable to farmers seeking to better manage soil C and N pools.