Regulated deficit irrigation promoting growth and increasing fruit yield of jujube trees

Abstract: Drought and water shortage have been the main factors restricting the sustainable and healthy development of jujube industry in the Northern Shaanxi Province. In the stage of crop growth, regulated deficit irrigation (RDI) can balance the degree of nutrition among each organ of plants, and lead to high fruit yield and quality and water use efficiency. This study investigated the effect of RDI on the jujube growth and its fruit yield under surge-root irrigation. The jujube (Ziziphus jujube Mill) widely cultivated in Yulin of Northern Shaanxi Province was selected for the field experiment in a jujube demonstration zone orchard in Yuanzhi village, Mizhi Country, in 2013. Three treatments of water deficit were designed in sprout leaves period and flowing and fruit-setting stage, respectively. The relative soil moisture of 70%, 60%, and 40% simulated mild, moderate and severe water deficit. The full irrigation with relative soil moisture of 80% was taken as control. During the experiment, the meteorological factors, including the wind speed, wind direction, air temperature, air relative humidity, atmospheric pressure, solar radiation intensity, and rainfall were monitored. Soil moisture was measured. Jujube panicle length, and vertical and horizontal diameter of jujube fruit were measured. The average weight of 100 jujubes was determined. The results showed that compared to the full irrigation, the mean soil moisture in 0-60 cm depth were reduced by 8.9%, 14.4% and 22.4% (P<0.05) for the treatments of mild, moderate, and severe RDI respectively. Compared to full irrigation, the jujube panicle length were reduced by 7.2%, 13.2% and 19.7% (P<0.05) for the treatments of mild, moderate, and severe RDI, respectively. During the period of the flowing and fruit-setting stage, the fruit growth was slow, which only reached 14.5% , 14.1%, 13.8% and 13.5% of the final volume of jujube fruit for the treatments of mild, moderate, severe RDI and full irrigation fruits, respectively. About 65% of jujube volume grew in the fruit enlargement stage. Compared with full irrigation, the yield of jujube has increased by 22.1% and 16.7% for mild and moderate RDI, respectively, but decreased by 9.5% for severe RDI. The jujube volume was highest for the mild RDI, followed by moderate RDI, full irrigation and severe RDI. The moderate RDI had the highest water use efficiency of 2.32 kg/m3, but the severe RDI had the lowest water use efficiency of 1.28 kg/m3. It suggested that the mild and moderate water deficit played an inhibitory effect on the growth of jujube panicle, and could reduce the amount of shoot growth and summer pruning. However, they could promote the growth of the fruit and increase yield during the sprout leaves period and flowing and fruit-setting stage of jujube. Among all the treatments, the mild water deficit of RDI had the best effects on jujube growth and yield.