Reserch On Water Requirement Threshold In Different Growth Periods Of Upland Jujube

Jujube could adapt to the local climate in the Loess Plateaus and produce high qualityfruit in the north of Shaanxi Province. Since the policy of returning land of farming to forest,the jujube cultivating industry has boosted quickly and has played a significant role inprotecting the local ecological environment. However, the semiarid climate in Yulin city couldnot meet the water requirement of jujube, especially in the flowering-fruit set and fruitswelling stage, which greatly contributed to the yield reduction and income loss, so, irrigationwould be the important mathod to increase the jujube yield. Therefore, it was important thatreserching the water requirement threshold in different growth periods of upland jujube torealize the accurate irrigation.The experiment was conducted with pear jujube in a jujube demonstration zone orchard,in Mengcha village, Mizhi County, Shaanxi Province, from2009to2011. The effect ofdifferent soil water potential (WPs) were studied on the jujube growth and development tofind the water requirement regular, and propose the suitable irrigation scheduling. The resultsshowed that:(1) Determining the change regularity of jujube trunk diameter in different growth stagesand the relationships between it and the different ecological factorsJujube trunk diameter fluctuated with different factors including the growth stage,climate, WPs and so on. In the daytime, the trunk shrank and got the minimum trunk diameter(MNTD) in the afternoon, while it recovered or expanded from the nightfall or night andfinally got the maximum trunk diameter (MXTD) in the dawn. In the cloudy day, themaximum diameter shrink (MDS) was obviously little.There were good linear regression relationship between the jujube MXTD and WPs,between the MNTD and WPs. The higher the WPs was, the higher the correlation coefficientwas. The poor linear correlation between the MDS and WPs indicated that the shrinkage ofjujube diameter mainly depended on the local climate and the tree itself.Additionally, jujube trunk diameter (TD) was extremely positive significant with relative humidity (RH), and its relationship with temperature (Ta) was extremely negative significant.However it was not significantly related to solar radiation (Rs). Therefore, RH and Ta werethe two major meteorological factors affecting the jujube trunk diameter. The direct andindirect effect of WPs, RH and Ta on jujube trunk diameter was analyzed by path analysis.The result showed that in high WPs (-44~-49kPa), WPs was the most direct factor andfollowed by RH, while in low WPs (-316~-385kPa), RH was the most direct factor andfollowed by WPs. In all WPs condition, Ta had little impact on the trunk diameter.(2) Determining the suitable water information indicator and the threshold for WPs indifferent stagesWith the method of ANOVA, the jujube MDS and MXTD and MXTD were respectivelyselected as the water-condition-indicator for flowering, fruit set and fruit swelling stage.All factors WPs had effect on were taken into consideration, including the amount offlower and fruit and yield treated as priority and trunk diameter micro-variation as secondary.The results showed that the lowest and uppest WPs respectively was-152kPa and-40kPa,-51kPa and-35kPa,-128kPa and-46kPa for flowering, fruit set and fruit swelling stage.(3) Determining the effect of WPs on jujube source-sink relationsDifferent WPs ranges in four plots were studied on source (trunk) and sink (fruit), theresult showed thar the WPs range (changed from-161kPa to-461kPa then recovered to-40kPa and got drier gradually) was a appropriate choice for the development of water-savingjujube industry, as only fruit could grew well in this WPs but the trunk growth was limited.(4) Determining the critical water requirement period and the irrigation thresholdCombined with the views of others that jujube was the most sensitive to water in fruit setand fruit swelling stage, called the critical water requirement period. The result showed that600m~3/hm~2was optimum amount of irrigation water and840m~3/hm~2was the maximum orluxurious amount of irrigation water.(5) Make clear the water requirement threshold of jujube tree based on the rainfallcharacteristic in YulinAfter analyzing, upland jujube water requirement from May to September was madeclear. Based on the rainfall characteristics in Yulin, drip irrigation was suggested to use, and inthe years with the average rainfall, the minimum irrigation in a year was360m~3/hm~2, themaximum was795m~3/hm~2, the optimum range was630～735m~3/hm~2.