EFFECT OF IRRIGATION AND NITROGEN-FERTILIZER ON YIELD, OIL CONTENT, NITROGEN ACCUMULATION AND WATER-USE OF CANOLA (BRASSICA-NAPUS L)

Effects of N application and water supply on yield, oil content and N accumulation by canola, cultivar Marnoo, grown on a heavy clay soil in the Goulburn Murray Irrigation Region were investigated. Treatments were rainfed (R(f)) or watered at a deficit of 50 mm (40-60 mm, I50) beginning in the spring. N treatments were 0, 50, 100 or 200 kg N ha-1 at sowing or as split applications of 20/80, and 50/50 kg N ha-1 at sowing and rosette, respectively. Yield (Y(g)) ranged from 170 to 520 g m-2. Irrigation and N increased yield in both years. Grain yields were increased by N application on the irrigated treatments when 100 or 200 kg N ha-1 was applied. Oil concentrations ranged from a maximum of 46.4% in treatment N0 to a minimum of 40.6% in treatment N200 and was inversely related to seed N concentration. Although fertilizer N decreased oil concentration, it increased the yield of oil. Nitrogen accumulation (N(b)) limited yield of all treatments and was described by the equation, Y(g) = 806[1-EXP(-0.039*N(b))]. This implied a decrease in yield per unit of N(b) at the higher rates of fertilizer addition with consequent increases in grain N concentration. The efficiency of water use in the production of grain (WUE(g)) and biomass (WUE(b)) were 7.5 and 23 kg ha-1 mm-1 respectively. Nitrogen additions increased WUE(g) and WUE(b) in both seasons. Maximum values of 8.9 (WUE(g) 1986) and 26.8 (WUE(b) 1987) were measured from treatment N200. These data suggest that the crops made efficient use of the applied water.