Recovery of Anhydrous Ammonia-Derived Nitrogen-15 During Three Years of Corn Production in Iowa
- C. A. Sanchez and
- A. M. Blackmer
Studies were conducted at two locations to determine recovery of anhydrous ammonia-derived I5N applied with and without nitrapyrin [2-ehloro-6-(trichloromethyI) pyridine] during corn (Zea mays L.) production over a 3-yr period in which N fertilizers were applied annually at rates commonly used in the Corn Belt. The results showed that 13 to 33% of the labeled N was removed from the plots during grain harvest in the first crop after application. Recovery of labeled N in the whole plants ranged from 29 to 45%, but the stover was returned to the plots. Nitrapyrin increased the amount of N recovered in plant tissue at only one of the six site years studied. Only small percentages (0.3-1.5%) of the labeled N were recovered in the second and third crops after application, and nitrapyrin had negligible effects on amounts of labeled N recovered by these crops. Analysis of soil samples collected 1 yr after application of labeled N showed that 19 to 23% of this N remained in the soil. Only small portions of this N existed as exchangeable ammonium and nitrate. Most of this N was in the KMI-N (Kjeldahl minus inorganic-N) fraction, which includes N from both organic matter and nonexchangeable ammonium. Large portions (47-94% of the labeled N found in the KMI-N fraction 1 yr after application were still present 3 yr after application. The results of this study show that a substantial portion (49-64% of the labeled N was lost from the surface 1.5 m of soil during the first year by processes other than plant uptake. A probable explanation as to why the losses reported here are greater than those reported from many comparable studies is that our determinations included the amounts of fertilizer N lost during the fall-tospring period. These losses must be considered when evaluating the long-term efficiency of N fertilization practices and the effects of these practices on environmental quality.
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