Response of pear-jujube to different soil water potentials during budding and flowering stages

Pear-jujube is widely cultivated in the Loess Plateau Region (LPR) of China where it is used to reforest farmlands. Pear-jujube culture was previously constrained by wasteful use of limited water resources that characterized traditional irrigation, restricting local agricultural development. It was therefore vital to study water demand at different growth stages of pear-jujube. This paper discussed the response of 4-year-old pear-jujube trees to different soil water potentials. Both vegetative and reproductive growth processes were studied in commercial pear-jujube orchards in Mengcha Village of Mizhi County, Shaanxi Province. Four levels of soil water potentials -31~-51 kPa, -41~-84 kPa, -59~-132 kPa and -161 kPa (no irrigation treatment) were set up to determine suitable soil water potentials at budding and flowering stages of pear-jujube. While soil water potential was measured using the equilibrium tensiometer (EQ15), trunk diameter fluctuation was measured using the linear variable displacement transformers (LVDT). The results showed that in different soil water potentials, trunk diameter fluctuation and vegetative and reproductive growths among treatments were significantly different (P < 0.05). During the budding stage, suitable soil water potential was in the range of -41~-84 kPa, in which pear-jujube vegetative and reductive growths were flourished with the least maximum daily shrinkage (MDS) among the treatments. However, the suitable soil water potential for pear-jujube flower bud differentiation was in the range of -41~-132 kPa. Although mild water stress did not adversely affect flower bud differentiation during budding stage, vegetative growth dropped and vegetative-reproductive growth relationship optimized. As at soil water potential range of -54~-78 kPa during flowering stage, MDS dropped to lowest point while fruit setting percent was highest. The most suitable soil water potential at pear-jujube flowering stage was therefore in the range of -54~-78 kPa. Also the most suitable soil water potential for pear-jujube fruit setting was in the range of -79~-114 kPa, in which fruit setting percent was highest. Hence at flowering stage, mild water stress increased fruit setting. At budding and flowering stages, water-logging and severe water-stress limited vegetative and reproductive growths and reduced fruit setting percent. However, water-logging enhanced trunk growth and severe water-stress retarded trunk growth. Furthermore, no real need of irrigating pear-jujube at budding stage was noted during normal years. This was because precipitation was enough for sprouting, lamina opening and flower bud development. However, precipitation alone was not enough at pear-jujube flowering stage during normal years.