Effects of different drip irrigation modes on water use efficiency of pear trees in Northern China

Unreasonable layout of drip irrigation systems and inappropriate irrigation decision-making methods in orchards in water-scarce areas in Northern China result in low water use efficiency (WUE). In order to reveal the effect of drip irrigation mode on WUE of orchards and improve efficient use of water resources, this study used pear (Pyrus pyrifolia cv. Whangkeumbae) as a test material to conduct a two-year field irrigation experiment, considering the two factors of drip irrigation pipes layout and lower limit of soil moisture,five drip irrigation modes and a control treatment (CK) were set up. By measuring the soil moisture content, water consumption, yield and fruit quality, the effects of different drip irrigation modes on spatial coefficient of variation (CV) of soil moisture, pear tree growth and WUE were evaluated. The results showed that the CV and the soil moisture content showed a significant linear negative correlation (p < 0.05), and the resulting difference in soil water, aeration and heat had an effect on the development of fruit tree roots. Five drip irrigation modes significantly reduced the ET value of pear trees and improved WUE compared with CK (p < 0.05). Among them, the mode of subsurface drip irrigation with double lines under soil moisture lower limit of 60% the field capacity (FC) worked best. Considering only the soil moisture lower limit, compared with 80% FC and 60% FC, the WUE of 70% FC increased by 13.04%, 7.56-12.21% respectively. However, the irrigation mode of 60% FC soil moisture lower limit effectively improved the fruit quality (soluble solids, titratable acid). Considering the factors of drip irrigation pipes layout, subsurface drip irrigation significantly increased WUE by 34.39-35.35% compared with surface drip irrigation (p < 0.05), and increased WUE by 16.36-24.77% compared with ring drip irrigation. The WUE of pear tree and the CV showed a linear positive correlation. Considering all aspects, we concluded that the mode of the subsurface drip irrigation with double lines under soil moisture lower limit of 60% FC was the best irrigation mode in pear orchard. The research results provide a typical reference for further research on perennial fruit trees to improve WUE.