FERTILIZER MANAGEMENT EFFECTS ON LEACHING OF LABELED NITROGEN FOR NO-TILL CORN IN-FIELD LYSIMETERS

The fate of labeled N fertilizer applied to no-till corn (Zea mays L.) grown in nonweighing lysimeters was determined for 3 yr after application to evaluate NO3-N leaching losses from point-injection and conventional N management systems. In 1984, N-15-enriched double-labeled urea-ammonium nitrate solution (UAN) at 200 kg N ha(-1) was either surface-banded or knifed-in at the V1 growth state. It was also point-injected at either 200 or 125 kg N ha(-1) in split applications at the V1, V5, and V9 growth stages. Labeled N as NO3-N was detected in drainage from the bottom of the lysimeters (1.37 m deep) with the first significant rain (54 mm) 7 d after application for all treatments. Greatest labeled NO3-N concentrations, however, occurred with drainage in the fall after harvest and in the spring of 1985, the year after application. In 1985 when unlabeled N was applied using the same four systems, average labeled NO3-N concentrations and annual losses were the greatest and ranged from 1.0 to 5.1 mg L(-1) and from 1.7 to 6.8 kg ha(-1), respectively; the ratio of labeled NO3-N to total NO3-N ranged from 0.08 to 0.25. Labeled NO3-N concentrations, losses, and ratios were smallest for the 125 kg ha(-1) point injected-split system for each of 3 yr. For all systems, about one-fourth of the applied labeled N remained in the soil profile at the end of the study. Total recovery (77%) and recovery in grain (48% in 1984) were also greatest for the 125 kg ha(-1) point-injected system and least for the surface-banded system (64 and 30%, respectively). Unrecovered N was believed lost through denitrification and ammonia volatilization from soil or aboveground vegetation.