Nitrogen Form Effects on Yield and Nitrogen Uptake of Rice Crop Grown in Aerobic Soil

Abstract

As an alternative production strategy, the cultivation of rice under upland condition is increasing in the areas where fresh water resource is limited during growing season. The main form of nitrogen (N) taken up by rice roots is shifted from ammonium (NH4) in flooded paddy soil to nitrate () in upland soil. A pot experiment was conducted in order to study the influence of to ratio on the yield and uptake of N by rice (Oryza sativa L.) grown under upland conditions. The sandy-loam soil (85-kg) used to fill each pot was mulched by semi-decomposed straw, and a total 4.8 g N per pot was supplied as a fertilizer topdressing at five ratios of -N/-N (0/100, 25/75, 50/50, 75/25, and 100/0). In comparison to provision of alone, supply of as the only N source produced higher number of effective ears and average weights of 1000 grains, but reduced the grain numbers in each effective ear. The total uptake of N and biomass yield per pot were 2.206 and 182.5 g from applying only , and 2.067 and 163.7 g from -N alone, respectively, while they reached 2.894 and 217.9 g when both forms of N were supplied in equal amounts. Soil -N concentration was constantly maintained at the range of 2–6 mg kg−1 during the vigorous growing period when the supply was less than 75% indicating little risk of N fertilization induced NO3 pollution in the rice-cultivated upland soil. The rice crop did not show a significant preference to the form of or alone. Provision of the dual N sources enhanced the growth and N use efficiency by rice crop cultivated in the upland soil.