[Effects of lower limit of subsurface drip irrigation on tomato growth and its yield in plastic tunnel]

A subsurface drip irrigation experiment was conducted in a plastic tunnel to study the effects of different lower limits of subsurface drip irrigation on tomato growth and its yield. The lower limits of subsurface drip irrigation were expressed by soil water suctions detected by tensiometers placed in 30 cm soil layer. The designed values of soil water suction in this experiment were 10, 16, 25, 40 and 63 kPa, respectively. The results showed that the height and biomass of tomato plant decreased significantly with increasing lower limits of subsurface drip irrigation. Parabolic regression curves were suitable to simulate the relationships of stem diameter of tomato plant, yield, and water use efficiency (WUE) with lower limits of subsurface drip irrigation. The relationship between the ratio of stem diameter to plant height of tomato and lower limit could be simulated by three-dimensional multinomial regression curve. The growth of tomato root and shoot and their ratio R/S) varied under different lowerlimits of subsurface drip irrigation. The tomato plant grew well, RI/S was favorable, and the yield and WUE were higher when soil water suction was in the range of 25- 33 kPa. When this range was served as the criteria for subsurface drip irrigation, the soil water content at the beginning of irrigation should be lower, and the irrigation frequency should be fewer than that of conventional irrigation. This range of soil water suction was in favor of improving the WUE and decreasing labor cost for tomato cultivation in plastic tunnel.