Effects of Controlled-Release Fertilizer on Corn-Corn and Corn-Soybean Rotations.

Corn (Zea mays L.) responds to nitrogen (N) fertilizer applications and there is potential to sync the availability of N from fertilizer with corn N demands to increase N use efficiency and yields. To test the effects of urea versus controlled-release, polymer-coated urea (ESN) on yields, we established six N treatments from 0 to 246 kg N ha-1 in a Fort Collins clay loam soil at the CSU ARDEC near Fort Collins, CO. We included 34 kg urea-N ha-1 as a starter in the ESN treatments. Both treatments were applied to irrigated corn grown in corn-dry bean (CB) (Phaseolus vulgarisL.) and continuous corn (CC) rotations. Nitrogen fertilizer increased yields of corn (P  < 0.0001). The ESN average yields of 9.4 Mg dry grain ha-1 were higher than the 8.8 Mg dry grain ha-1 with urea  (P 0.08). The corn yields of the CB were the same for the ESN and urea treatments. Total grain and aboveground N content were higher with the ESN than the urea for both the CS and CC rotations (P < 0.05). The CB average yields of 10.5 Mg dry grain ha-1 were higher than the 9.1 Mg dry grain ha-1 with the CC (P < 0.001). These preliminary results suggest that at current corn prices the ESN could potentially be a viable, economical source of N for CC. These responses suggest that the slow N release from the ESN contributed to higher yields with the CC, and higher aboveground N content with the CC and CS.  Both ESN and legume residue contributed to increased yield and helped sync available N with crop N uptake at the 134 kg N ha-1 for CC and 67 kg N ha-1 for CB. Synchronizing N fertilizer applications with plant demand using controlled-release fertilizer can increase crop nitrogen recoveries and yields.