Yield, irrigation response, and water productivity of deficit to fully irrigated spring canola

Canola (Brassica napus) is an oil-seed crop that is adapted to the northern High Plains of the USA and is considered a viable rotational and biofuel crop. However, decreased ground water allocations have necessitated determining the impact of limited irrigation on canola productivity. The objectives of this research were to determine the effects of a range of irrigation from none to fully irrigated on yield, oil content, soil water changes and water productivity of spring canola. The study was conducted for four growing seasons at three locations in western Nebraska. Two sites had sandy soils whereas the other was a silt loam. Glyphosate tolerant canola was planted late March to early April. Cumulative irrigation treatments were 0, 100, 200, and 300mm of water with the highest rate adjusted to be non-ET limiting. Canola extracted soil water from depths greater than 1.2m in both fine textured and sandy soils making it a good alternative for deficit irrigation. Canola responded well to irrigation during dry years but showed little response in above average precipitation years. A water use efficiency of 7.6kgmm−1 with a threshold of 123mm was observed. Canola seed yield ranged from 440 to 3280kgha−1 with 165 and 582mm of cumulative ET. During drier years, canola exhibited peak values in water use at 8–9 weeks after planting. Deficit irrigation reduced ET and yield and hastened maturity during drier years. Oil content was increased by irrigation during drier years with no effect shown when precipitation was above average. Oil content ranged from 30 to 50% depending on year and irrigation level. The water response provided benefits of not only higher yield, but also higher oil content which makes deficit irrigated canola an attractive alternative production and biofuel crop for this region.