Study On Characteristics Of Wetting Body Under Drip Irrigation For Jujube Forest In Loess Hilly Region In North Of Shaanxi

Shortage of water resources is the major factors of limiting the sustainable development in the Loess Plateau region. Jujube in the southern hilly region of Yulin as an important industry, which is the main source of income. Its development to a large extent constrained by the drought and water shortage. In order to increase the yield of jujube, Northwest Agriculture and Forestry University in 2006 implemented the Mountain jujube forest micro-irrigation technology research and demonstration project, which technology has reached synchronization solution to prevent soil erosion and the effect of drought and water shortage. It is also obtained increasing effect. Drip irrigation has become the key measure to improve ecological and economic profit of jujube in mountain.The research was on the characteristic of wetting body, which is under the condition of drip irrigation will help to correct the drip irrigation system design and make a high level of field water management.This paper will mainly discuss the water movement in undisturbed soil under drip irrigation. The experiment studied on the impact of number of different emitters, dripper discharge, irrigation duration and emitter spacing on wet body shape, size, moisture, the regulation of wetting front migration, and the effects of water distribution. It put forward to a simple forecast of the experimental model which is the characteristic value of soil moisture body, basing on characteristics of five years old jujube trees'root distribution, identifying suitable dripper discharge and irrigation duration. It has provided a basis for the local irrigation system design and operation of drip irrigation system, which also made an important guiding for management of drip irrigation technology in the north of Shaanxi, as well as application of other economic forest. And the preliminary research results were obtained as follows: (1) The horizontal and vertical advance distance of soil wetting front conforms to power function of infiltration time for point source drip irrigation under different dripper discharge .through analyzing the relationship between equation fitting coefficients and dripper discharge, the model were established to predict the horizontal and vertical advance distance of soil wetting front.(2) The shape of the wetted soil zone in Water infiltration process is closed to oval. The maximum horizontal advance distance of soil wetting front is 5-20cm below the surface, and the higher dripper discharge is, the location of the maximum horizontal advance distance is deeper. So the wetted soil volume calculated with the semi-ellipsoid computation formula need to be revised.(3) The Average of volumetric water content increment△θis a constant independent of infiltration time, during the course of point source infiltration under drip irrigation. The value of△θis more and more high with the increasing of dripper discharge.(4) The higher dripper discharge is, the average moisture content of wetting body is higher under the same irrigation amount; the longer irrigation time lasting, the volume of wetting body is bigger under the same dripper discharge at the end time of drip source infiltration. The relation ship between Soil water content and the distance from the emitter is quadratic polynomial in the horizontal direction and vertical direction underside of emitter.(5) The relation ship between infiltration distance and the infiltration time is power function on the intersection side under the two-point source infiltration. The shape of the wetted soil zone under point source infiltration is half ellipsoids, and the shape of the wetted soil zone under two-point source infiltration is ribbon distribution which is parallel to capillary pore. The change between those two shapes is transitional.(6) If there were no evaporation and no root water exaction, the wetting front advance rate is less than 0.2cm/h 48h after the end of irrigation, at this time, the wetting front advance rate is so small that the soil water redistribution is mostly ended. There is good liner relation ship between the characteristic values of 48h later after the irrigation and the moment the irrigation is ended.(7) The shape of the wetted soil zone in soil water redistribution process is closed to oval, and the wetted soil volume calculated with the semi-ellipsoid computation formula need to be revised. Take the correction factor as 1.19 when the drip discharge is smaller than 8L/h. The soil water redistribution decreased the significant differences in wetted soil volume of different drip discharge. The wetted soil volume is mainly affected by the irrigation amount after water redistribution.(8) After the soil water redistribution, higher drip discharge made a positive effect to increasing the soil water content of nearby panel point, while the lower drip discharge is favorable to the vertical movement of water. Under same drip discharges, extended irrigation time lasting makes few efforts to the soil water content of nearby panel points; in contrast, it makes a great effort to the soil water content of distant panel points.(9) The higher irrigation amount and longer irrigation time lasting made the water of the wetted soil zone distributed well, and the soil water content would matched well to the suitable water content of the jujube-tree under the following two conditions, higher irrigation amount or longer irrigation time lasting or the both.(10) If the planned moisture layer is less than 80cm, and considering the factors of irrigation lasting time and radius of diffusion, take 4-6L/h as the drip discharge and 8-10h as the irrigation time lasting for loessial soil in north of shaanxi.