Effect of deep placement of nitrogen fertilizer on growth, yield, and nitrogen uptake of aerobic rice

Recent studies have reported that poor growth of aerobic rice associated with urea induced ammonia toxicity when applied at early growth stage. The objective of this study was to examine the effect of different methods of nitrogen application on plant growth of aerobic rice grown in continuous aerobic rice system. Micro-plot experiment was conducted in 2008 dry season in a field where aerobic rice has been grown for fourteen seasons in International Rice Research Institute (IRRI) farm. Two Pot and pot-diffusion incubations experiments were done with the soil from same field where micro-plot experiment was conducted and aerobic rice has been grown for 14 seasons in greenhouse and growth chamber. Apo, an upland rice variety, was grown under aerobic conditions with different application method of nitrogen in field and pot experiments. The field micro-plot experiment showed that urea and urea super granules (USG) deep placement increased grain yield of aerobic rice by 1.66 t ha-1in continuous aerobic rice cultivation. Pot experiments studying the effects of different application methods of nitrogen indicated that N incorporation into soil and placement at a depth of 5-10cm in the soil increased the vegetative growth parameters, and plant growth parameters of aerobic rice under ammonium sulfate were significantly higher than urea at all applied treatments. In pot-diffusion incubations experiment, N placement at a depth of 5.0 cm in the soil significantly reduced nitrogen loss by ammonia volatilization. Our results suggested that there is a possibility of improving aerobic rice yield in the continuous aerobic rice system by using right N source or changing conventional method of nitrogen application to deep placement.