Evapotranspiration and Crop Coefficient of Transplanted Cotton after Wheat Harvest

Abstract

【Background and objective】 Cotton-winter wheat rotation is a common cultivation in the Yellow River basin, but there is an overlapping period during their growing seasons. One technology is to nurture cotton seedlings in seedling beds and then transplant the seedling after the wheat is harvested. The objective of this paper is to study evapotranspiration and crop coefficient (Kc) of the transplanted cotton under different irrigation methods. 【Method】 The experiment was conducted in 2020 and compared surface irrigation and drip irrigation. Evapotranspiration of the transplanted cotton was measured continuously using a large-scale transpiration meter. The reference evapotranspiration was calculated using the Penman-Monteith formula, and the Kc was calculated as their ratio. 【Result】 Compared to surface irrigation, drip irrigation promoted crop growth and increased its leaf area index (LAI) as a result. There was no significant difference in evapotranspiration between the two irrigation methods due to the influence of rainfalls. The growth-season evapotranspiration under drip and surface irrigation was 420.79 mm and 415.30 mm, respectively. In the early growth stage, the ratio of surface evaporation to evapotranspiration for the surface and drip irrigation was in the range of 46.06%~90.23% and 42.24%~77.46%, respectively. Correlation analysis found that daily average temperature (T), total radiation (Rs) and saturated water vapor pressure (VPD) were positively correlated with the evapotranspiration. The Kc of the transplanted cotton after wheat harvest differed from that of directly drilled. As the plant grew, the Kc increased first followed by decline after maximizing in the middle growth stage. The Kc at the early, middle and late growth stage was 0.91, 1.23 and 0.71, respectively under surface irrigation, while under drip irrigation the associated Kc was 0.91, 1.26 and 0.64 respectively. Regardless of irrigation treatments, the Kc increased first followed by flattening due to the gradual increase in LAI. The relationship between Kc and LAI were Kc=1.663LAI0.058 7 with R2=0.664 for the surface irrigation, and Kc=1.177 9LAI0.061 1 with R2=0.694 for the drip irrigation. 【Conclusion】 The evapotranspiration of the transplanted cotton increased from seedling to flowering boll stage and then declined gradually after the flocculation stage. Its Kc at the early growth stage was significantly higher than that recommended by FAO-56.

Keywords

• transplanted cotton after wheat harvest
• evapotranspiration
• soil evaporation
• crop coefficient