Improved water use efficiency and fruit quality of greenhouse crops under regulated deficit irrigation in northwest China

Water limit is the major bottleneck that restrains sustainable development of agriculture in northwest China. In order to obtain higher water use efficiency (WUE) and improve fruit quality of greenhouse crops with less water, experiments with regulated deficit irrigation (RDI) on watermelon (Citrullus vulgaris; 2008-2010), hot pepper (Capsicum annum L.; 2011-2012) and tomato (Solanumlycopersicum L.; 2008-2013) in solar greenhouse were conducted in Shiyang River Basin of arid northwest China. Results showed that the feasible growth season of watermelon for high WUE and better fruit quality was in the winter-spring season with total irrigation amount of 114 mm. The specific irrigation water were 25, 12, 62 and 15 mm, respectively at seeding stage, plant-stem elongation stage, fruit bearing-expanding stage and fruit mature stage. It also showed that the positive relationship between hot pepper yield and seasonal evapotranspiration (ET) was fitted by linear model under drip irrigation, but exhibited an exponential relationship under furrow irrigation. The better RDI strategy for pepper to improve both WUE and fruit quality was maintaining soil water content at 70% of field capacity (θf) throughout the growth season except at the late fruit bearing and harvesting stage. At this stage, sufficient water (90% θf) should be applied. Results of tomato also suggested that the ventilation of greenhouse should be good around 1-3 pm in the local arid condition in northwest China. Mean values of Pn and Tr were decreased by 27.6% and 27.0% under irrigation quota of 214.2 mm, but leaf water use efficiency (WUE) significantly increased with comparison to quota of 260.8 mm. Moreover, the maximum values of yield and total water use efficiency (WUEET) of tomato were obtained at 89.5% and 77.0% of maximum ET, respectively. There are linear regression relationships between relative fruit quality parameters and relative ET, which provided a scientific basis for water-saving crop production in greenhouse. Application of such RDI strategy on greenhouse crops has great potential in saving water, maintaining economic yield and improving WUE and fruit quality.