The effect of nitrogen fertiliser on yield, nitrogen and mineral elements in Australian brown rice

The average yield of rice crops grown by the 2300 producers in southern Aus tralia has ranged from 6.5 to 9.4 t/ha over the last 5 years. Average yield s in the northern Murrumbidgee Irrigation Area have exceeded 10 t/ha in sev eral of these years with individual producers attaining yields greater than 12 t/ha. Further increases in yield are expected with new genotypes, such as Namaga released in 1997. These high yielding crops require access to lar ge amounts of nitrogen (and other elements) from the soil and fertilisers. Inputs of other nutrients are relatively minor and limited to phosphorus (P ), sulfur (S) and zinc (Zn). In the current study, we evaluate the relations between yield increase due to nitrogen (N) fertiliser applications, and the rate of removal of element s by medium and long-grain genotypes. Some significant differences were fou nd between genotypes in the concentration and accumulation of some minerals . In the 1993-94 experiment, the long-grain genotype Langi yielded higher a nd had higher mineral concentrations than Pelde, the lower-yielding genotyp e it replaced. However, no consistent relationships emerged between genotyp e, yield and mineral concentration or accumulation. Nitrogen applications c aused significant increases in yield, grain nitrogen and some mineral conce ntrations. In the 1992-93 and 1993-94 experiments, 125 kg and 100 kg nitrog en fertiliser increased yield by 63% and 71% (from 6.8 to 11.1 t/ha and fro m 5.9 to 10.1 t/ha), respectively. The same N application rates increased t he nitrogen concentration in the grain from 12.9 g/kg to 14.5 g/kg in 1992- 93, and from 11.4 g/kg to 12.6 g/kg in 1993-94. Grain S was significantly i ncreased in 1992-93 from 1.04 to 1.21 g/kg, and from 0.82 to 0.94 g/kg in 1 993-94. The concentrations of grain Mn also increased significantly with N application in the 1993-94 season. Total accumulation of all minerals (exce pt B and Na in 1992-1993 and Cu in 1993-1994) increased with N application. Yield increase, driven by N fertiliser, was the major influence on increas ed export of N, S, P, K, Mg, Ca, Fe, Mn and Zn from the soil.