To investigate the drought tolerance of pear-jujube (Ziziphus jujuba Mill.) trees and their
responses to soil water moisture after stumping, pot and field experiments had been
conducted 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 from
wilting to death of pear-jujube under continuous water stress was studied. Next, the
responses of pear-jujube trees to different soil water moistures after stumping were studied
with four different soil water treatments in two years. Some preliminary conclusions have
been drawn as follows.
(1) The average value of initial wilting coefficient of pear-jujube was 2.49%, while the
average value of apparent permanent wilting index was 1.49%. Pear-jujube had strong
ability of drought resistance since the wilting coefficient of pear-jujube was much lower
than that of other jujube varieties or plant species. In addition, the lethal drought point of
pear-jujube was 1.25% and lethal time was 135 ± 11 days. The permanent wilting
coefficients of pear-jujube varied from 1.25% to 1.49%, which represented a narrow range
of moisture contents rather than a certain value.
(2) It was correct to use the apparent permanent wilting index to describe the ability of
drought resistance of trees. The apparent permanent wilting index of pear-jujube was more
practically valuable than the real permanent wilting coefficient. Rewatering the plant at its
apparent permanent wilting index could keep it from the risk of death. Under natural
conditions, drought stress usually could not lead pear-jujube to dead.
(3) At the budding and flowering stages, stumping not only strengthened the growth of
jujube tree but also improved fruit set percentage. The height and crown width of
pear-jujube trees were higher than those before stumping in the very year. The average
length and number of bearing braches and average leaf areas were all lower than those
before stumping. The number of flower bud decreased by 52.4% after stumping, while the
fruit set percentage increased by 1.69 times. (4) At the budding and flowering stages, post-stumping water consumption of
pear-jujube trees was smaller than that of pre-stumping. The soil water moisture of
post-stumping increased by 2.88% compared with that of pre-stumping. The purposes of
saving water and improvement of water use efficiency could be achieved. The suitable soil
water potential was -41～-69 kPa during the shoot period after stumping. While, the
suitable soil water potential was -59～-72 kPa for pear-jujube during the flowering period.
Moreover, it was useful for post-stumping pear-jujube trees to set fruit when suitable soil
potential was -72～-112 kPa. The growth of stem was not affected when soil water potential
was greater than -461 kPa.
(5) During fruit development period, stumping improved yield in treatments of high
water moisture. Under the treatment T1 with highest water moisture, the post-stumping fruit
abscission rate was a little greater than that of pre-stumping, while the single fruit weight
and yield increased by 40.8% and 29.6%. The single fruit weight of treatment T3 increased
by 28.5% after stumping. However, the yields of T2 and T4 declined when the average level
of water potential reached -97.0 kPa.
(6) Stumping could reduce the amount of irrigation and water consumption, while
maintaining jujube fruit production at the same level. Although the average fruit drop rate
increased by 11.1% after stumping, the number of fruits increased by 2.8% and the overall
yield remained stable. At the same time, the amount of irrigation decreased from 201.4 to
108.0 mm, or 46.4%. Water consumption decreased from 172.8 to 149.4 mm, or 13.5% after
stumping. This is important for the development of jujube forests of high yield and quality
and 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 would
be affected after stumping when the average level of water potential was below -215.8 kPa.
High rate of fruit drop and low unit fruit weight could occur. At fast-fruit growing stage, the
atrophy of trunk would not rehabilitate after stumping when the average water potential was
below -287.2 kPa. The suitable soil water potential for fruit development was -45.0～-61.0
kPa for pear-jujube after stumping.
Key words: pear-jujube, soil water potential, stumping, drought lethal point, drought