Nitrogen-15 and bromide tracers of nitrogen fertilizer movement in irrigated wheat production

In irrigated agricultural systems, NO3 leaching is believed to result from high fertilizer rates combined with the need to periodically leach salts fr om surface soil horizons. The purpose of this research is to estimate N fer tilizer movement in the soil of commercial fields of flood-irrigated wheat (Triticum spp.) while documenting best management practices (BMPs), Potassi um bromide and N-15 labeled ammonium sulfate were applied as tracers of N f ertilizer movement to 1- X I-m microplots replicated 9 or 10 times in three commercial fields of flood-irrigated wheat. The soil was sampled at harves t to a depth of 2.4 to 4.0 m. More fertilizer was applied at two out of thr ee sites and more irrigation water was applied at all sites than recommende d by BMPs, Bromide recovery in the soil and plant tissue at harvest was 29, 68, and 61% of that applied at the three sites. Most of the UN measured in the soil profile was contained in the 0- to 0.3-m increment of soil. Recov ery on N-15 in the soil and plant tissue at harvest was 54, 54, and 69% of that applied. The Br recovery data suggests that 32 +/- 28% (standard devia tion) of the N-15 applied may have leached. The highest leaching potential was measured at the site that adhered to BMPs for N fertilizer management b ut had the most permeable soil. Nitrate leaching in flood-irrigated wheat p roduction seems inevitable even if BMPs for N fertilizer management are fol lowed.