CORN UPTAKE AND SOIL ACCUMULATION OF NITROGEN - MANAGEMENT AND HYBRID EFFECTS

Inefficient use of fertilizer N by corn (Zea mays L.) can result in the accumulation of excessive amounts of NO3- subject to leaching losses in the crop root zone. The fate of fertilizer N as influenced by N rate, nitrapyrin [2-chloro-6-(trichloromethyl)pyridine], and corn hybrid was evaluated in a 3-yr study with sprinkler-irrigated corn. Variables were fertilizer-N rate (75, 150, and 300 kg N/ha); nitrapyrin (0 and 0.5 kg/ha); and corn hybrid (Pioneer hybrids 3377, 3475, and 3551). Nitrogen was applied as late-sidedressed (V6-V9) NH3. The fate of fertilizer N was evaluated by measurement of apparent fertilizer-N uptake (AFU), form of N in the fertilizer band prior to and following anthesis, and accumulation and distribution of N in the soil profile. There were no significant effects of hybrid on AFU across years, and no significant hybrid X nitrapyrin interactions on AFU. Nitrapyrin significantly reduced AFU across N rates and hybrids in 2 of 3 yr. Nitrate-N concentrations in the fertilizer band, in the presence of nitrapyrin, were reduced prior to anthesis in 1986. Higher NH4+-N concentrations in the fertilizer band in 1986, as well as trends towards higher total inorganic-N concentrations all 3 yr following anthesis, suggest mineralization of temporarily immobilized fertilizer NH4+. Reduced AFU in the presence of nitrapyrin in 1986 and 1987 indicates reduced availability of fertilizer N consistent with a temporary immobilization process. Nitrate accumulation in the soil to a depth of 1.8 m after three growing seasons indicates a trend toward less NO3- accumulation where nitrapyrin was applied at N rates of 75 and 150 kg/ha. Nitrate concentrations in the soil at a depth of 1.8 m were significantly greater at the 150 and 300 kg N/ha rates, compared with the 75 kg N/ha rate or unfertilized soil, indicating probable movement of fertilizer N below the 1.8-m depth at the higher rates. These results indicate that nitrapyrin should not be applied with NH3 at late-sidedress time for this soil.