Study On Drought Tolerance Of Pear-jujube Trees And Their Responses To Soil Water Moisture After Stumping

To investigate the drought tolerance of pear-jujube (Ziziphus jujuba Mill.) trees and theirresponses to soil water moisture after stumping, pot and field experiments had beenconducted in the Jujube Water-saving Demonstration located in Mizhi County, Yulin City,Shaanxi Province in China. This study included two main contents. First, the process fromwilting to death of pear-jujube under continuous water stress was studied. Next, theresponses of pear-jujube trees to different soil water moistures after stumping were studiedwith four different soil water treatments in two years. Some preliminary conclusions havebeen drawn as follows.(1) The average value of initial wilting coefficient of pear-jujube was2.49%, while theaverage value of apparent permanent wilting index was1.49%. Pear-jujube had strongability of drought resistance since the wilting coefficient of pear-jujube was much lowerthan that of other jujube varieties or plant species. In addition, the lethal drought point ofpear-jujube was1.25%and lethal time was135±11days. The permanent wiltingcoefficients of pear-jujube varied from1.25%to1.49%, which represented a narrow rangeof moisture contents rather than a certain value.(2) It was correct to use the apparent permanent wilting index to describe the ability ofdrought resistance of trees. The apparent permanent wilting index of pear-jujube was morepractically valuable than the real permanent wilting coefficient. Rewatering the plant at itsapparent permanent wilting index could keep it from the risk of death. Under naturalconditions, drought stress usually could not lead pear-jujube to dead.(3) At the budding and flowering stages, stumping not only strengthened the growth ofjujube tree but also improved fruit set percentage. The height and crown width ofpear-jujube trees were higher than those before stumping in the very year. The averagelength and number of bearing braches and average leaf areas were all lower than thosebefore stumping. The number of flower bud decreased by52.4%after stumping, while thefruit set percentage increased by1.69times. (4) At the budding and flowering stages, post-stumping water consumption ofpear-jujube trees was smaller than that of pre-stumping. The soil water moisture ofpost-stumping increased by2.88%compared with that of pre-stumping. The purposes ofsaving water and improvement of water use efficiency could be achieved. The suitable soilwater potential was-41～-69kPa during the shoot period after stumping. While, thesuitable soil water potential was-59～-72kPa for pear-jujube during the flowering period.Moreover, it was useful for post-stumping pear-jujube trees to set fruit when suitable soilpotential was-72～-112kPa. The growth of stem was not affected when soil water potentialwas greater than-461kPa.(5) During fruit development period, stumping improved yield in treatments of highwater moisture. Under the treatment T1with highest water moisture, the post-stumping fruitabscission rate was a little greater than that of pre-stumping, while the single fruit weightand yield increased by40.8%and29.6%. The single fruit weight of treatment T3increasedby28.5%after stumping. However, the yields of T2and T4declined when the average levelof water potential reached-97.0kPa.(6) Stumping could reduce the amount of irrigation and water consumption, whilemaintaining jujube fruit production at the same level. Although the average fruit drop rateincreased by11.1%after stumping, the number of fruits increased by2.8%and the overallyield remained stable. At the same time, the amount of irrigation decreased from201.4to108.0mm, or46.4%. Water consumption decreased from172.8to149.4mm, or13.5%afterstumping. This is important for the development of jujube forests of high yield and qualityand the alleviation of soil desiccation to ease in the dry and rainless North Shaanxi.(7) At fruit development period, normal growth and development of pear-jujube wouldbe affected after stumping when the average level of water potential was below-215.8kPa.High rate of fruit drop and low unit fruit weight could occur. At fast-fruit growing stage, theatrophy of trunk would not rehabilitate after stumping when the average water potential wasbelow-287.2kPa. The suitable soil water potential for fruit development was-45.0～-61.0kPa for pear-jujube after stumping.