Evapotranspiration and crop coefficient of drip-irrigated winter wheat in China's Xinjiang Province

Abstract

Drip-irrigated winter wheat (Triticum aestivum) is grown on 5.07×105 ha in China's Xinjiang Uyghur Autonomous Region. Information about evapotranspiration (ET), evaporation, and crop coefficient (Kc) is important for maximizing water savings in drip-irrigated wheat. A field experiment was conducted during two winter wheat growing seasons at the Shihezi University Agricultural Experiment Station, Xinjiang Province. The study included three irrigation amounts (375, 600, and 750 mm, abbreviated D1, D2, and D3, respectively). The results showed that the ET of drip-irrigated winter wheat generally increased as irrigation increased. Averaged across both growing seasons, average daily ET rates decreased significantly in the order D3 (2.64 mm/d) > D2 (2.26 mm/d) > D1 (1.55 mm/d). Evaporation was greatest between 1 and 4 days after irrigation and accounted for 26-28% of ET during the entire growing season. The Kc values ranged between 0.45 and 1.35 across all growth stages, averaging 0.96. A fourth-order polynomial equation (R2 > 0.75) describes the changes in Kc across the growing season. A logarithmic function (R2 > 0.96) described the relationship between Kc and the leaf area index. The average yield was greater in D3 (10 520 kg/ha) than in D2 (10 060 kg/ha) and D1 (8000 kg/ha) in both years. The water use efficiency in D1 was 1.14-1.16 times that in D2, and 1.27-1.30 times that in D3. Thus considering the yield, the water use efficiency, and the harvest index, the optimum irrigation amount was 600 mm. These results are helpful for improving irrigation management and crop water use predictions in Xinjiang Province and elsewhere in the world with similar irrigation methods and climatic conditions.