Effects of drip irrigation uniformity and amount on soil moisture and tomato yield in solar greenhouse

Drip irrigation is an important factor associated with the water and fertilizer integration technology. The uniformity of drip irrigation is an important performance index to measure its quality. Therefore, choosing the appropriate drip uniformity can achieve the dual targets of cost effectiveness as well as high crop yield. A field experiment was carried out from October 2016 to April 2017 in the Yangling Agricultural Hi-tech Industries Demonstration Zone, Shaanxi Province, China. Experimental treatments applied in the split plot design included:three irrigation quantities in Zone A (190 mm, 220 mm, and 250 mm), and three drip irrigation uniformities in Zone B (65%, 75%, and 85%). In the early stages of planting test, no crop experiment was set up in the same area with only the drip irrigation belt laid, and the experimental treatments were also applied in a split plot divided into main treatment (Zone 1) and sub-treatment (Zone 2). The Zone 1 was treated with three irrigation quantities-5 mm, 10 mm, and 15 mm; and in Zone 2, the same there drip irrigation uniformities to Zone B were set. The results showed that when the irrigation uniformity was between 65% and 85%, the mean soil moisture uniformity during entire growth period was higher than the highest drip irrigation uniformity (85%) approximately. The influence of drip irrigation uniformity on the uniformity coefficient of soil moisture was enormous. There was a significantly linear relationship (P < 0.05) with determination coefficient of 0.918 between the mean soil moisture uniformity and the three factors i.e., irrigation quantity, irrigation uniformity, and initial soil water content. When the initial soil moisture was approximately 60% of the field capacity, and the irrigation amount was less than 15 mm, the interaction between the drip irrigation uniformity and the irrigation amount was linear (P < 0.05) and significantly related to the soil moisture uniformity. In other cases, there was no significant association. The irrigation amount had significant effect on tomoto, the irrigation uniformity and their interaction had no significant effect on tomato yield. Taking into account the yield and use efficiency of irrigation, the combination of irrigation amount of 220 mm and drip irrigation uniformity of 75% was the optimal one. Considering the economics and reliability of the system, the method involving small amount of multiple irrigation should be chosen. This was also suggested for the reduction in the standard of drip irrigation uniformity in the Northwest China.