the Roots: New Legume Cover Crop Research

— Written By NC State Extension

Leguminous cover crops such as crimson clover and Austrian winter pea provide significant quantities of plant residue material that build up the soil organic matter pool and furnish essential plant nutrients such as nitrogen for subsequent field crops. Maintaining soil organic matter in field crop production is crucial as organic matter improves soil nutrient and water holding capacity and overall soil structure. An improved understanding of the persistence of cover crop derived organic matter in the soil can increase our knowledge of the effectiveness of different cover crops in contributing to long-term soil organic matter. Most research involving cover crop residue contributions to soil organic matter has focused entirely on the aboveground portion of cover crops, while the contribution of root systems has been neglected. Cover crop root systems can be quite extensive and their chemical composition tends to favor slower rates of decomposition and longer-term persistence in the soil than above ground residues. Considering their potential to contribute to long-term soil organic matter, it is important that we research the persistence and decomposition dynamics of leguminous cover crop root systems.

Field experiments involving the decomposition of crimson clover, Austrian winter pea, and hairy vetch roots under different cover crop kill methods have been initiated in the last year at the Center for Environmental Farming Systems (CEFS) in Goldsboro as well as in Kinston. The two kill methods that have been employed are disking, which works the cover crop into the soil and roller-crimping, which leaves the cover crop on the surface as a mulch. Root decomposition measurements under these different kill methods will be taken throughout the summer into early fall. The results of this field study will give us a better idea which cover crop species root systems contribute the most to long-term soil organic matter as well as how different kill methods affect the rate and, hence, the long-term persistence of root systems in the soil organic matter pool.

In addition to this field experiment, we also are conducting a greenhouse study comparing the root system morphology (root length and diameter) of crimson clover, Austrian winter pea, and hairy vetch. Past research has indicated that root systems of different diameter classes decompose at different rates with finer roots (small diameter) decomposing much faster than larger roots. There is also evidence showing differences in chemical composition between roots of different diameters with finer roots having a composition more favorable to rapid decomposition. Our hope is that this greenhouse-based root morphology experiment will improve our understanding of which cover crop species have the largest root systems and how these root systems compare to one another in terms of morphology. This can increase our predictive power concerning the rate of root system decomposition of these different species. Preliminary results indicate that crimson clover has the largest root system as well as the greatest proportion of fine roots. We hope to build upon this root morphology research this fall by testing how decomposition is affected by soil nitrogen status.

Given the importance of roots in contributing to long-term soil organic matter, investigating the decomposition dynamics of cover crop root systems is a worthy cause and should provide pertinent information relevant to producers that utilize leguminous cover crops as a component of their soil fertility management program.

Updated on Feb 26, 2014
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