NITROGEN UPTAKE BY PADDY RICE (ORYZA-SATIVA L) FROM N-15 LABELED COATED UREA AND AMMONIUM-SULFATE

In Japan, intensive farming in upland and paddy fields requires very expensive agricultural materials (including fertilizers), cultivation machines, and labour. Hence, the recent demand for the reduction of the cost of farming has resulted in a change in the system of field management. The reappraisal of slow-release fertilizers is one of such trends. Reduction in the frequency of fertilizer application enables to reduce the labour cost. Although slow-release fertilizers are rather expensive, a controlled, efficient uptake of fertilizers is beneficial for plant growth and also for environmental protection. Some slow-decomposing N fertilizers, such as isobutylidene diurea (IB), guanylurea (GU) etc. have been used in Japan. Sulfur-coated urea (SCU) was studied in some countries (Wells and Shockley 1975). Among the slow-release fertilizers recently developed in Japan, urea coated with polyorefin type resin (PCU) releases urea by diffusion through small pores on the coat surface. The rate of N release depends essentially on the soil temperature (Fujita and Maeda 1977). In paddy fields, for example, the nitrogen of coated urea is released during the active vegetative and reproductive stages during which the temperature is high. The release of N from coated urea is adopted to the active N uptake of rice plants, and the loss by denitrification and ammonia volatilization, and immobilization of coated urea N is expected to be smaller than in the case of ammoniacal fertilizers (Allen 1984). Use of surface films of long chain alcohols on paddy soils may be an alternative method to reduce the N loss, but the effect seems to be short-lived (Cai et al. 1987). © 1990 Taylor & Francis Group, LLC.