Effects of schedules of subsurface drip irrigation with air injection on water consumption, yield components and water use efficiency of tomato in a greenhouse in the North China Plain

In order to WA the effects of schedules of subsurface drip irrigation (SDI) with air injection on tomato, two years experiments with three-factors and three-levels were carried out in a spring and summer greenhouse at North China Plain. Three factors were depth of drip belt buried, amount of irrigation water based on the water evaporation of an diameter of 20 cm pan and frequency of air injection. Each factor contained three levels. Results showed that this three factors had significant effects on soil evaporation (E-s). Total E-s decreased with deeper depth of drip belt buried, smaller amount of irrigation water and greater frequency of air injection. The greatest intensity of daily soil evaporation occurred at seedling stage of tomato. In line with this, total evapotranspiration (ET) decreased significantly with deeper depth of drip belt buried and smaller amount irrigation water as well but the effect of air injection on ET was not significant. Furthermore, the greatest water consumption period of tomato was during its flower and fruit period, and the proportions of total E-s accounting for total ET was about 20% similar to 30%. Thus, pan coefficient (K-p) values should be changed according to water requirement of tomato at different phenological stages in practice to achieve a greater water use efficiency (WUE), and the relationship between irrigation water amount and ET was a significant positive linear correlation. As for the yield components of tomato, depth of drip belt buried and amount of irrigation water consistently affected yield components of tomato over two years experiments but its sequences of levels were different in both years. However, the effect of air injection on tomato yield was only effective in one of two years. Based on these findings, some conclusions could be made that optimized ET of tomato under SDI was about 290 mm and proper WUE was about 45 similar to 50 kg/m(3) at which the highest yield would be harvested, and the most effective depth for burying drip belt was 20 mm, and recommended K-p should be changed at seedling stage (0.5-0.8), flower and fruit stage (1.0-1.2) and the end of growth stage (0.5-0.8).