The increased irrigation frequency

The increased irrigation frequency under the three micro-irrigation systems improved the soil water conditions at the top soil layer, especially during the grainfill stage. The soil water storage for the top 1 m soil profile was averagely 20 mm greater under two irrigation applications using micro-irrigation methods than that B-90 around 10 days after anthesis. Therefore, the more soil stored in the top 1 m soil layer under the increased irrigation frequency would have the benefits to increase the soil water availability to the crop during the later growth stages of the crop.3.3. Crop water use, yield and WUE under different irrigation treatmentsCrop water use (ET) was listed in Table 3 for different irrigation treatments across the 2012–2015 seasons. Water use and the yield of the crop were affected not only by the irrigation management, but also by the seasonal weather conditions and stored soil water. The lower ET0 in 2012–2013 season resulted in the lower ET for the irrigated treatments, as compared with that in 2013–2014 season. Although rainfall in 2013–2014 season was small, the relative higher soil water contents at sowing contributed greatly to the ET. Due to the dry summer before planting winter wheat in 2014–2015 season, the contribution of SWD to ET was reduced under rainfed condition as compared with other seasons. On Average, SWD contributed 60–80% of the seasonal ET for the rainfed treatment, 40–60% under limited irrigation and 20–50% under increased water supply condition. ET was increased with the increase in irrigation amount and the contribution of the soil water stored before sowing was reduced.Table 3. Crop water use (ET), soil water depletion (SWD), yield and water use efficiency (WUE) under different treatments for the three seasons of winter wheat*.