Plant tissue test for determination of optimum concentration and uptake of nitrogen at different growth stages in lowland rice

Nitrogen (N) deficiency is one of the most important yield limiting nutrients in lowland rice and plant tissue analysis is an important criteria for diagnosis of nutritional disorders in crop plants. The objective of this study was to determine optimum concentration and uptake of N in lowland rice (Oryza sativa L.) at different growth stages. A field experiment was conducted during 3 consecutive years in the central part of Brazil on a. Haplaquepts. Nitrogen rates used were 0, 30, 60, 90, 120, 150, 180, and 210 kg N ha(-1). Nitrogen concentration in the shoot at different growth stages was significantly (P<0.01) affected by N fertilization. Optimum N concentration for maximum dry matter yield was 43.4 g kg(-1) at initiation of tillering, 34.6 g kg(-1) at active tillering, 12.7 g kg(-1) at initiation of panicle, 12.8 g kg(-1) at booting, 11.0 g kg(-1) at flowering, and 6.5 kg(-1) at physiological maturity growth stage. In the grain, the optimum N concentration was 10.9 g kg(-1). Nitrogen uptake varied from 16 to 185 kg ha(-1) in the shoot from initiation of tillering to flowering. At physiological maturity, N uptake was 71 kg ha(-1) in the shoot and 76 kg ha(-1) in the grain. Accumulated N at harvest or physiological maturity produced 9545 kg ha(-1) straw and 6450 kg ha(-1) grain yield. Shoot dry weight increased with the increase in shoot N uptake up to flowering. At harvest, N uptake in the shoot decreased due to translocation to the grain. Rice needs N during its whole growth cycle, however, relatively initiation of panicle, flowering and physiological maturity were the most critical growth stages for N tissue analysis to define optimum N concentration or N uptake for maximum shoot or grain yield.