Winter rye cover crop biomass, nutrient uptake, and quality in response to fall and spring N fertilization

Growers in Illinois often apply manure or add starter fertilizers that contain nitrogen (n) in the fall to save time for other farming operations in the spring. Fall manured fields sometimes receive a starter n in spring as part of the operation. We hypothesized that winter rye (Secale cereale) (wr) cover crop could capture the applied n which in turn changes wr dry matter (dm) biomass, nutrient uptake, and c accumulation capacity, and wr quality (ash, lignin, and c concentrations along with c:n, and lignin:n ratios). Two separate trials with randomized complete block design at two separate locations in Southern Illinois were conducted in 2020 and 2021. Trial one had two rates of fall-applied n (0 vs. 56 kg n ha−1), and trial two had initial fall manure to all plots plus four rates of n fertilizer in spring (0, 23, 47, and 71 kg ha−1). Results for trial one indicated that fall n fertilization had no effect on wr biomass, nutrient uptake, and quality parameters due to loss of applied n in the fall. Spring n application did not affect wr dm biomass but linearly increased n, phosphorus (p), and potassium (k) concentrations, their uptake, c concentration, and decreased c:n and lignin:n ratios. We concluded that spring n fertilization could facilitate n decomposition of wr by decreasing its c:n and lignin:n ratio and help increasing the wr nutrient uptake capacity, but fall n application should be avoided to prevent n loss to the environment and decrease the cost of operation.