Nitrogen Uptake Efficiency In Furrow-Irrigated Corn Using 15 N Urea.

Corn (Zea Mays L.) is becoming an increasingly important row crop in the Mid-south. In Arkansas furrow irrigation is the primary irrigation method and corn is often planted on beds that are as wide as 97 cm in either single or twin-row configurations. Nitrogen fertilizer is the largest line-item input cost for most producers and can represent as much as 28% of total operating costs. Current recommendations suggest that 1/3 of the N be applied preplant with the remainder applied prior to the V8 growth stage. In a recent survey, producers indicated they were utilizing a three-way split where an additional pre-tassel application of N was being included to help increase yields. To date there have been no studies investigating the fertilizer N use efficiency (FNUE) of furrow irrigated corn in Arkansas using direct stable isotope methods, but with the spike in corn acreage and the input costs associated with N fertilizer a study was initiated. Field studies were established in 2011 and 2012 at the Southeast Research and Extension near Rohwer, AR to determine the FNUE using ¹⁵N labeled urea. The study was designed to compare the FNUE based on the rate and time of application with a comparison of both a two-way and three-way split. The efficiency of N fertilizer was influenced by rate and time of application. The application of N pre-tassel did not increase corn yields, but did result in the highest FNUE of any treatment near 98%, when the preplant and sidedress N was deficient. The highest yielding treatment included a preplant and sidedress N application and resulted in a FNUE value of 66.5%. These results indicate that FNUE of furrow irrigated corn can be very high, but the correct rate and timing of application must be optimized in order to maximize yield and efficiency.