NITRAPYRIN EFFECT ON CORN N-15 UPTAKE EFFICIENCY, DENITRIFICATION AND NITRATE LEACHING

The effect of nitrapyrin on the fate of fertilizer nitrogen (N) applied to soil needs further investigation. Our objective was to determine the effect of nitrapyrin under two different leaching regimes on the fate of ammonium sulfate-nitrogen [(NH4)2SO4-N] added to the soil, namely corn N uptake, denitrification, nitrate leaching and soil residual N. A Nunn sandy clay loam soil (fine, montmorillonitic, mesic, aridic, argiustoll), low in residual inorganic N was used. Nitrogen-15 enriched (NH4)2SO4 (5 atom% N-15) was applied at five rates (0, 50, 100, 200, and 400 mg/kg), nitrapyrin at three rates 0, 1.3, and 2.6 mu L/kg (0, 2.36, and 4.72 L/ha) and leaching at two rates (0 and 1000 mL over field capacity in two 500-mL increments at 3 and 6 weeks after planting) in a complete factorial arrangement with three replications. Corn (Zea mays L.) seeds were planted in pots (2 kg soil/pot) and allowed to grow for 80 days in a greenhouse. The atom% N-15 values were determined in plant tops, leachates and soil samples using a mass spectrometer. The results showed that N fertilizer increased dry matter production, plant N concentration, leaching of nitrates and denitrification significantly. The effect of nitrapyrin on yield was not statistically significant, but, it at a rate equivalent to 4.72 L/ha reduced denitrification and nitrate (NO3) leaching and increased N uptake efficiency. Application of 4.72 L/ha of nitrapyrin versus control showed the following results respectively, N uptake: 46.3 versus 39.6%, denitrification: 26.3 versus 35.3% and NO3 leaching: 2.7 vesus 6.7% of fertilizer N-15. Nitrapyrin increased soil residual fertilizer N-15 in organic matter and roots. The result of this study show that application of nitrapyrin at an adequate rate decreases denitrification and NO3 leaching and increases N uptake efficiency.