Lowland rice response to nitrogen fertilization

Nitrogen deficiency is one of the most important nutritional disorders in l owland rice producing areas around the world. Nitrogen fertilizer recommend ations for lowland rice (Oryza sativa L.) varieties grown on Inceptisols ar e limited. The objective of this study was to evaluate the response of lowl and rice (cv. Metica 1) to added N and to determine N use efficiency and nu trient accumulation during the crop growth cycle. A field experiment was co nducted during 3 consecutive years in the central part of Brazil on a Hapla quept Inceptisol. Nitrogen levels used were 0, 30, 60, 90, 120,150, 180, an d 210 kg N ha(-1). Nitrogen fertilization significantly increased dry matte r and grain yield. Ninty percent of the maximum grain yield (6400 kg ha(-1) ) was obtained with the application of 120 kg N ha(-1) in the first year of experimentation. In the second and third years, 90% of the maximum yields (6345 and 5203 kg ha(-1)) were obtained at 90 and 78 kg N ha(-1), respectiv ely. Yield components were also significantly affected by N treatments. Among yield components, panicle length and panicle number m(-2) had highest correlations with grain yield (r = 0.70** and 0.78**); maximum grain yield across the 3 years was achieved at about 583 panicles m(-2). Dry matter pr oduction and grain yield at the highest N level (210 kg N ha(-1)) across th e 3 years were 9423 and 6389 kg ha (1), respectively. At this grain + straw yield, the rice crop accumulated 139 kg N, 26 kg P, 218 kg K, 36 kg Ca, 24 kg Mg, 850 g Zn, 5971 g Mn, 125 g Cu, 4629 g Fe, and 104 g B. Nitrogen use efficiency defined in several ways, decreased with increasing N rates. Agr onomic efficiency across 3 yeras averaged over N rates, was 23 kg of grain produced per kg of N applied. Physiological efficiency was 146 kg biologica l yield (grain + straw) produced per kg of N accumulated across the 3 year and N rates. Average agrophysiological efficiency was 63 kg grain produced per kg of N accumulated in the grains plus + straw. Apparent N recovery eff iciency was 39% across the 3 years and N rates. Average nitrogen utilizatio n efficiency was 58 kg of grain produced per kg N utilized by the rice crop . Soil pH and calcium concentration in the soil decreased significantly at higher N rates, whereas, soil Al3+ level was significantly increased after the harvest of the third rice crop.