Root and Shoot Biomass and Nutrient Composition in a Winter Rye Cover Crop.

Nitrogen loss from applied fertilizer can be a significant economic loss in corn (Zea mays L.) production systems as well as environmental quality issue if nitrate reaches surface or ground water. Winter cereal rye (Secale cereal L.), a commonly used cover crop in corn systems, has potential to scavenge soil NO₃–N through a fibrous root system. The objective of this study was to quantify root and shoot biomass, C, and N partitioning in rye cover crop at the time of termination in the spring. This was a one–year study conducted at a site with a no-till corn–soybean [Glycine max (L.) Merr.] rotation, rye drilled in the fall following grain crop harvest, and three N rates applied to corn (0, 135, and 225 kg N ha^–1). Rye root biomass to 60-cm depth following corn, and 30-cm depth following soybean, was estimated using ingrowth tubes installed in the fall after rye seeding and removed at the time of rye termination. For rye following corn and soybean, 48 and 62 %, respectively, of the total root biomass was present in the top 15-cm depth. Overall, biomass, C and N content of the shoots were significantly greater than for roots, with approximately two times more shoot than root material and only 33–36 % of total plant C and 17–18 % of total plant N in the root biomass. The C:N ratio of root biomass was high (47–52), and at least double the shoot biomass C:N (16–23). These results show that the largest fraction of rye N uptake is contained in the aboveground rye biomass. However, with high C and low N content, and high C:N ratio of the rye roots, inorganic-N from soil or degrading shoot biomass could be immobilized with root degradation and therefore reduce potential N recycling.