Corn Yield and Nitrate Loss in Subsurface Drainage from Midseason Nitrogen Fertilizer Application

Abstract

Whether in response to remotely sensed plant N status or as a rescue treatment when previously applied N has been lost to denitrification or leaching, there is growing interest in applying N to corn at midseason. While the yield benefits of this practice are variable, little information is available as to the impacts of midseason N application on water quality. We compared grain yields and NO₃ losses in drainage water as a result of applying N either once after emergence or equally split between just after emergence and midseason (V16). Nitrogen treatments consisted of 199 (H), 138 (M), and 69 (L) kg ha⁻¹ applied postemergence (V1–V3), and 69 kg ha⁻¹ applied postemergence and again at midseason (R). Grain yield for corn (Zea mays L.) and soybean [Glycine max (L.) Merr.], grown in a 2-yr rotation, and drainage water NO₃ concentrations were measured on replicated tile-drained plots in a producer's field from 2002 through 2005. Midseason application of additional N resulted in 0.9 and 2.5 Mg ha⁻¹ greater yield than the L treatment in 2002 and 2004, respectively; however, yield was greater when the same total amount of N was applied in one application shortly after emergence (M treatment) vs. the split treatment. There was no carryover effect on subsequent soybean yields for any of the N treatments. Annual flow-weighted NO₃ concentrations in tile drainage were consistently greater (0.3–1.3 mg L⁻¹) for the R treatment than the M treatment and significantly greater when averaged across all years. Residual soil NO₃ at the end of the year also indicated that some of the midseason N application was not taken up by the crop and was available for leaching. Thus, midseason N application was beneficial for recovering some of the potential yield in corn when initial N applications are insufficient for optimum yield, but the practice did not benefit water quality in this study compared with a single application at emergence.