Effect of irrigation and nitrogen fertilizer on yield, oil content, nitrogen accumulation and water use of canola (Brassica napus L.)

Abstract

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.