Estimating Translocation of Urea-N in Furrow-Irrigated Corn Using 15N.

Corn (Zea mays L.) is becoming an increasingly important commodity for producers in the Delta region of Arkansas. In Arkansas, corn producers typically use furrow-irrigation and apply ~ 1/3 of the total recommended N preplant. Nitrogen uptake efficiency of preplant urea-N in furrow-irrigated corn is highly influenced by application rate and application method. Preplant N that is not incorporated into the bed prior to planting is prone to loss via runoff. Loss of N from surface runoff can contribute to adverse environmental impacts of adjacent water bodies and reductions in water quality. The objective of this study was to determine the lateral movement of urea-N¹⁵ as influenced by rate (34, 67, and 100 kg N ha^-1) and method of application (incorporated, in-furrow, and surface broadcast) in a furrow-irrigated production system. Soil samples were collected from a 0-10 cm depth within fertilized plots and within the furrow downslope from the fertilized plots. Samples were analyzed for TN and atom% N¹⁵ to determine the extent to which urea-N¹⁵ was translocated beyond the fertilized plot area. Results indicate that urea incorporated into the bed resulted in the lowest quantifiable movement of urea beyond the plot boundaries compared to the in-furrow and surface broadcast applications regardless of application rate. Surface-applied urea that was not incorporated was susceptible to movement within the furrow beyond the plot boundary, but resulted in less than 13% loss from fertilized area. There was no quantifiable translocation of N from soil samples taken >4.5 m beyond the fertilized plot area and the highest mass of fertilizer N recovered within the 4.5 m beyond the fertilized plot for all treatments was 4.6 kg N ha^-1. These results indicate that N rate and application strategy influence urea-N¹⁵ movement within furrow, but little fertilizer N is translocated down-furrow regardless of rate or application.