Date of Graduation


Document Type


Degree Name

Doctor of Philosophy in Crop, Soil & Environmental Sciences (PhD)

Degree Level



Crop, Soil & Environmental Sciences


Trenton Roberts

Committee Member

Cliff Snyder

Second Committee Member

Nathan Slaton

Third Committee Member

Jeremy Ross

Fourth Committee Member

Mike Richardson


15N, cover crops, nutrient recycling, root biomass


Cover crops can provide many benefits to cropping systems including erosion control, weed suppression, and increased soil organic matter. Regardless of the intended goal for using cover crops, the changes to the nutrient flux in a cropping system caused by cover crops retaining and recycling nutrients needs to be considered in order to maximize the productivity of the following commodity crops. This research encompassed complementary greenhouse, field, and laboratory experiments to evaluate nutrient uptake and release by tillage radish (Raphanus sativus) and cereal rye (Secale cereale) cover crops, as well as the subsequent early-season recovery of recycled nutrients by the following corn (Zea mays) crop. When grown under controlled greenhouse conditions, tillage radish and cereal rye cover crops recovered, at most, 38% of the applied fertilizer N, and most of the captured N was translocated and stored in the shoots, which produced greater biomass than the roots. Cereal rye generally recovered more N, P, K, and Zn than tillage radish due to greater biomass accumulation; however, by the V6 growth stage corn following tillage radish usually produced more dry matter and contained more N, P, K, and Zn than corn planted into cereal rye residue. Early season corn growth and nutrient uptake following cereal rye was often lower than that of corn planted into no cover crop. The fertilizer N recovery efficiency of cover crops grown in the field study was, at most, 60%, and the application of fertilizer N did not always increase corn nutrient uptake. Results from the laboratory incubation study revealed that tillage radish released available N earlier in the growing season than cereal rye residue. By the end of the incubation 43% of the total N (TN) contained in the residues was recovered as NO3-N. Incorporating cover crop residues increased the rate at which NO3-N accumulated during the later stage of the incubation trial (42 to 179 days). Based on results from this study, tillage radish cover crops provide a more optimum timing of nutrient release in alignment with early-season corn nutrient demand than cereal rye.