Cover Crop Root Composition and Density in a Long-Term Vegetable Cropping System Trial

The contribution of cover crop roots to soil dynamics is poorly understood, in part because little information is available on the distribution, depth, chemical compositional changes over time, and nutrient mineralization rates of typical cover crop roots. A study was conducted to investigate the role of cover crop roots in a long-term trial on the effects of cover crop species and seasonal placement on soil properties in a vegetable rotation. Root length density (RLD), chemical composition, and nitrogen mineralization during incubation were measured in roots of red clover (Trifolium pratense L.) and winter rye (Secale cereale L.) of varying ages. Nearly 50% of the fine root RLD was measured in the top 5 cm for all roots, with no significant differences between species and ages. Lignin concentration in red clover roots increased nearly four-fold as they aged from 4 to 24 months, while N concentration were 22% lower in the older roots. N concentration decreased by 50% in rye roots from 0 to 9 months, leading to doubling of C:N. During incubation, net N mineralization was greater from 24 month-old red clover roots than 12-month roots, while winter rye roots showed net N immobilization over the incubation period.