EFFECT OF NITROGEN (NH4 NO3) SUPPLY ON ABSORPTION OF AMMONIUM AND NITRATE BY CONVENTIONAL AND HYBRID RICE DURING REPRODUCTIVE GROWTH

Although NH4+ has generally been accepted as the preferred N source for fertilising rice, some workers have concluded that NO3- is as effective as NH4+. The present glasshouse study examined the relative uptake of NH4+ and NO3- from solution and cultures containing 5-120 mg N/L supplied as NH4NO3 by a hybrid rice (India) and a conventional rice cultivar (Japonica). At all levels of N supply, the hybrid rice had higher leaf area and higher rates of uptake of total N than the conventional cultivar. Net photosynthesis rates were similar for both cultivars at the highest rates of N supply, but were lower at 5-40 mg N/L for the hybrid cultivar than for the conventional cultivar. At all levels of N supply, the conventional rice cultivar absorbed more NH4+ than NO3-. In contrast, the hybrid rice absorbed more NH4+ than NO3- at the low levels of N supply (5-40 mg N/L), but more NO3- than NH4+ at the high levels of at 80 and 120 mg N/L. It is concluded that the uptake of N by rice is under genetic control and also dependent on levels of N supply. Thus the appropriate form of N by rice is under genetic control and also dependent on levels of N supply. Thus the appropriate form of N fertiliser for rice may depend on cultivar and rates of N supply.