N15-tracer studies of the transformations, movement, and recovery of anhydrous ammonia-derived N in the rooting zone of corn

Sanchez, Charles
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Field studies were conducted for three years at two sites in Iowa to acquire a better understanding of the transformations and movement of anhydrous ammonia-derived N in soils and the response of corn (Zea mays L.) to this N. Because nitrification inhibitors have been widely recognized as having potential for improving the efficiency of N fertilization, the effects of nitrapyrin (the most widely used nitrification inhibitor) on the transformations and movement of fertilizer N were also studied.;Recoveries of labeled N in the grain ranged from 13 to 33% in the first crop after fertilization. All plant materials except grain were returned to the plots. Only small percentages (0.3 to 1.5%) of the labeled N were recovered in the second and third crops after fertilization. These findings suggest that fertilizer N applied for one cropping season has little residual value in subsequent cropping seasons where fertilizers are applied each year.;Analysis of soil samples collected one year after fertilization showed that 19 to 23% of the fertilizer N remained in the soil. Only small portions of this N were as exchangeable ammonium and nitrate. Because low recoveries of fertilizer N could not be attributed to lateral movement of labeled N from the plots, it must be concluded that 49 to 64% of the fertilizer N was lost from the rooting zone during the first year by processes other than crop removal. The distributions of fertilizer-derived nitrate observed in the rooting zone during the growing season showed that leaching was a major mechanism of N loss. As much as half of the fertilizer N was rapidly incorporated into forms other than exchangeable ammonium and nitrate. Much of this N was released during the growing season.;Nitrapyrin had little effect on the amounts of fertilizer N recovered. This compound had adverse effects on plant growth under some conditions. The results indicate that, in order to realize the economic and environmental benefits of nitrification inhibitors, more work is needed to identify the appropriate amounts of N that should be applied with these compounds.