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

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.