Effect of nitrogen (NH4 NO3) supply on absorption of ammonium and nitrate by conventional and hybrid rice during reproductive growth

Abstract

Although NH4 + has generally been accepted as the preferred N source for fertilising rice, some workers have concluded tha NO3 - is as effective as NH4 +. The present glasshouse study exmined 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 fertiliser for rice may depend on cultivar and rates of N supply.