Comparative study on the response of Indica and Japonica rice plants to ammonium and nitrate nitrogen

Abstract

The effects of NH₄ ⁺ and NO₃ ^- as nitrogen sources on the growth of two subspecies of rice, Oriza saliva subsp. Indica and Oriza saliva subsp. Japonica, during the first 6 weeks of growth were studied by the water culture method. The results obtained indicated that Indica and Japonica rice plants respond differently to NO₃ ^-. Although both Indica and Japonica grew fairly well in solutions containing the two forms of nitrogen, the growth of the former was superior in NO₃ ^- than in NH₄ ⁺+NO₃ ^- or NH₄ ⁺ solutions, especially at relatively low nitrogen concentrations, whereas the growth of the latter was inferior in NO₃ ^- than in NH₄ ⁺+NO₃ ^-solutions. In addition, plants of both subspecies fed with NH₄ ⁺ showed growth retardation wtih tip-burning of the lower leaves and poorly branched roots. On the other hand, under moderately warmed glass house conditions with natural sunlight in winter, the growth of Indica in NO₃ ^- solution was appreciably reduced compared to that in NH₄ ⁺+NO₃ ^-. Thus, the effects of climatic conditions such as temperature and intensity of sunlight on the response of rice plants to NH₄ ⁺ and NO₃ ^- nitrogen appear to be very important.