| Many domestic reseachers found that artificial forest and grass land lead to soil desiccation and the phenonmenon became serious with the increasing tree age. In addition, the Returning farmland to forest(grass) policy in China made soil water ecological deterioration. But there is no report on how to restore dry soil layers and how to avoid soil deterioration. The research aim is to determine soil water characteristics for different years old jujube plantations, the relationship for soil moisture and root distribution, pruning intension and Transpiration water consumption, and jujube water consumption regulatory under controlled conditions. using locating monitor, sampling in the field, limiting supply water, potting experiment and field large-scale earth pillar; Also, the main purpose is to explore high efficient water use for non-irrigated jujube plantation by water-saving pruning techniques and dry farming techniques. There were main results listed as follows:1) The results of soil water study showed that the whole soil water profile was stratified into three layers: active layer, difficult recovery layer, and stable layer according to soil water fluctuation.The active layer ranges in the 0-200 cm with obvious monthly dynamic change of soil water. In May, soil water content is the lowest during the whole growth stage(from May to October); soil water content increases greatly in July and it reaches the maximum value in October. The soil water increasing trend is similar to the jujube water consumption trend. This indicates that the stage for jujube vigorous growth is the period that soil water enhanced greatly, but the minimum value of soil water appears in the germinating stage and dormant ending stage. The difficult recovery layer is below 200 cm and the depth range for this layer depends on the age of jujube plantation. When jujube age increasing, the depth for difficult recovery layer is also increased. Water consumption depth could reach 540 cm for jujube aged twelve; leading to a difficult recovery range of 340 cm. below the difficult recovery layer, there is the stable layer. Therefore, the water consumption depth for dense jujube plantation is less than the depth for Robinia pseudoacacia, caragana microphylla, and alfalfa. In the future, those planting pattern will pose a positive effect on regulating and controlling soil moisture for local crops in the semiarid hilly regions.2) The research on jujube rooting system showed that the maximum root depth of the 12-year-old jujube was 520 cm. The difference between the maximum and minimum root depths for twelve-aged trees was 180 cm. Lateral roots started developing intersection networks three years after planting. Soil water fluctuation was not induced by vertical root systems of dense-dwarf jujube plants. With increasing jujube stand age, root depth, dry soil layer depth(below 240 cm) and annual soil water variance within the top 0-200 cm soil layer increased. However, soil moisture in the root-zone decreased when jujube tree age increased and dried soil layer depth was slightly greater than rooting depth. The results of this study have important significance to provide vital technical support for jujube cultivation especially under semiarid conditions and were expected to find application in water management for plantations in the semiarid hilly regions of the Loess Plateau.3) The study on soil water consumption showed that The amount soil water storage for the difference between twelve-year old jujube plantation and cropland within 0-1000 cm was 129.31 mm, indicating that the annually soil water for twelve-year old jujube plantation was10.76 mm. the reason why dried soil layers formed in the local areas was extra water consumption for jujube plantation(10.76 mm annually). According to the water controlling experiment, five-year old jujube plantation had the highest water use efficiency at the yield of 13703 kg hm-2, the jujube size would be the sample for the following prune to reduce Evaporation water consumption caused by tree size. Soil water consumption of 1 and 3 year old Jujube stands was similar to farmland soil water consumption in September, so Jujube plantations of these ages may grow normally, depending on the local annualrainfall. The greatest amount of water consumption(393 mm) occurred by 5 and 7-year old Jujube trees, indicating that the amount of rainfall was not sufficient for normal growth. However, beyond this level of water consumption, unrechargable, dried soil layers formed indicating that these yields(20,400 kg ha-1) may exceed the maximum water carrying capacity. For 9-year old Jujube plantations, yield decreased to 15,000 kg ha-1, but the depth of soil water did not increase and the water consumed for growth at this stage came solely from local precipitation. Therefore, a reasonable water consumption target for local Jujube plantations is 393 mm in order to maintain sustainable yields(15,000 kg ha-1).Apparent initial wilting of jujube appeared at 2.49% soil water content and final death under 105 days of continuous drought. At soil water content of 1.29% combined with 27 days of continuous drought and then followed by re-watering, jujube could survive rather than to die. Under 337 mm irrigation in the growth season, the maximum yield of the 5-year-old jujube was 14336 kg ha-1. And the maximum water production efficiency at 286 mm water supply was 42.69 kg ha-1 mm-1. The stem-cutting method of managing jujube plantation enhanced soil water content recovery. This investigation not only laid a significant technical basis for the management of plantations, it also provided a useful insight into effective preservation of soil water, which could profoundly benefit cultivated land ecology in semiarid areas.4) The results of water-saving measurements showed that white polythene mulching can enhance soil water content effectively, but weeds growing under polythene could consume surface soil water. And black film mulching was better to recover soil water and no weeds grow under film. Compared with bare land, the area removing weeds have lower soil water content within 0-120 cm, so removing weeds can enhance soil water content. the soil water content depths under branches mulching and rainwater harvesting ditch treatments can reach 260 cm, and 340 cm and the rainwater harvesting ditch has stronger effect on soil water regulation. Jujube transpiration water consumption can be effectively reduced by pruning branches to control specifications and lowering leaf area index, which is beneficial to soil water adjust, so, this is a new way for dry farming jujube plantation. It is suggested that combined water-saved pruning and rainwater harvesting ditch techniques; dwarfed dense Jujube plantation would recover its soil water in Semiarid Loess Hilly Areas. The study is significant to soil moisture ecological restoration as well as sustainable development of forestry in semiarid areas. |
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