Effects of deficit irrigation regimes on the yield and growth of oilseed rape (Brassica napus L.)

Experiments were carried to determine the effect of deficit irrigation regimes on grain and oil yield, seasonal evapotranspiration, yield response to water, water use efficiency and plant growth of oilseed rape (Brassica napus L.) in the Trakya region of Turkey. The experiments were conducted on a clay-loam Entisol soil and the regionally most popular variety of oilseed rape (Bristol) was used. A randomised complete block experimental design with three replications was used. Three well-known growth stages of the plant were considered using a total of 8 (including rain-fed) irrigation treatments. The effect of irrigation and water stress at any stage of development on grain yield, thousand grains weight, oil yield and plant growth components were evaluated. Results showed that oilseed rape was significantly affected by water stress during the sensitive flowering stage. The greatest irrigation and total water use efficiency for grain yield were 71.6 and 7.7 kg ha−1 mm−1, respectively, when the crop was irrigated once after flowering. Therefore, under conditions of water scarcity, such as occurs in the Trakya region of Turkey, if irrigation is to be applied only once, then at the flowering stage is preferable. However, when water from winter precipitation is stored sufficiently in the soil profile and regular rainfall occurs until mid-April, deficit irrigation omitting irrigation at the flowering stage (yield formation and ripening) will lead to a loss of yield. The highest yield was obtained from the treatments that were not stressed during the flowering, yield formation and ripening stages. Seasonal irrigation water use and evapotranspiration were 251 and 715 mm, respectively, for the non-stressed treatment. Oilseed grain yield from this treatment was 4.80 t ha−1. The seasonal yield response factor value was 0.87 (coefficient of determination, R2 = 0.71).