Absorcion de nitrogeno en trigo en relacion con la disponibilidad hidrica | Nitrogen uptake of wheat in relation to water availability

In the Pampa Region in Argentina, fertilization and supplementary irrigation have recently been introduced. New studies are needed to know the effect of these practices. The objectives of this study were to determine the real recovery of N provided by the 15N-urea and to estimate the N evolution in a wheat-soybean rotation system with different water availability. 15N-labeled urea was applied at different rates (0 and 50 kg N ha(-1) in 1997, and 0, 60, and 120 kg N ha(-1), in 1998) to wheat grown in a Typic Argiudol in Pergamino (Rolling Pampa). The experimental design included supplementary irrigation. The irrigation was evaluated only during 1998 because excessive rains occurred during the wheat growth season in 1997. Losses of biomass and yield were observed during the rainy year (1997). During 1998, the urea use efficiency was determined by the method of the difference between N content in fertilized and non-fertilized plants. The real or "effective" recovery of N from 15N-urea was measured by the isotopic method. A strong relationship between climatic conditions and the fertilizer use efficiency was observed. Mineralization of native N was enhanced by fertilization under adequate water availability. The effective recovery of 15N in the crop was low (18 to 23% of applied N), but there was little variation with different water availability. The recovery of 15N in soybean cropped after wheat showed that N from the fertilizer was recovered in the following crop. In these cases, N from fertilizer can be temporarily immobilized in organic pools, which are mineralized in subsequent seasons. Fertilization strategies, in soils where immobilization and remineralization processes are so important, must be elaborated taking into account these processes, specially when irrigation is used.