| Walnut trees is the main type of fruit trees at Aksu region in Xinjiang. By the end of 2015, the planting areas of forest fruit at Xinjiang have reached 13,330,000hm2. Among them,walnut planting areas have reached 3,000,000hm2. However,there are some problems such as low irrigation efficiency and waste water resource.Irrigation strategy is one of the most important methods to solve those problems. Therefore, at the background of development of fruit industry and irrigation efficiency, 7-year-old walnut trees were chosen as the research object for the field experiments,and 150m3/hm2(C1 treatment), 300m3/hm2(C2 treatment) and 450m3/hm2(C3 treatment) were set. Through the comparison of canopy parameters under different irrigation quota, the best irrigation quota treatment was selected. In order to improve the overall irrigation level of walnut and to alleviate the pressure of water supply,the whole growth period of irrigation system was made at the end. The conclusions are described as follows:(1)During the period of walnut fruit expanding, C2 had significant effect on leaf area index. However, the values of light transmittance, DSF and ISF under C1 and C3 treatment were much greater than that of C2 treatment. At the middle and late growth stage, C2 and C3 treatments had more significant effect on radiant energy interception than C1 treatment. With the growing of fruits, there was a constant increase on leaf area index and value of radiant energy interception, which finally became stable, and the parameters of light transmittance, direct site factor and indirect site factor were decreased continuously. By comparison, leaf area index in 2015 was much greater than those in 2014. Leaf area index and irrigation quota could significantly influence the production of walnuts. It was concluded that the irrigation quota of 300m3/hm2 under drip irrigation could ensure the optimal production and best economic benefit.(2)The analysis of the spatial distribution of root system indicated that the roots 0cm-60 cm under the soil and 0cm-60 cm away from the tree were densely distributed.(3)Both daily transpiration intensity and daily water demand presented a parabola change trend, the value of which maximized during the oil conversion period. During different growth phases, the values of daily transpiration intensity and daily water demand were expressed as C3 treatment>C2 treatment>C1 treatment. The values of daily evaporation intensity did not change obviously. There were different values in walnut trees. Daily transpiration intensity, daily evaporation intensity, and daily water demand were closely related to leaf area index and established the relationship of one variable multiple regression.(4)In the process of numerical simulation with HYDRUS-2D, comparison between the measured values and simulated values indicated that the assessment indicators of RMSE and ME were within a reasonable range, which proved that HYDRUS mode could be used in the actual experiment researches.(5)The primary field irrigation experiment of HYDRUS-2D simulation showed that the infiltration of irrigation water in 3 treatments were different. As irrigation was completed, the flow infiltration of C1 treatment was much shallower, and the wetting front did not reach the area that the roots were densely distributed. The conditions of C2 treatment and C3 treatment were the same with each other. The irrigation surface of irrigation water could percolate uniformly into the roots areas. But when the water saving irrigation was taken into consideration, C2 treatment was better at arid area.(6)With the premise of irrigation quota in 300m3/hm2, the fine root distribution and lower limit of soil volumetric water content were used as evaluation standards, and the change law of volumetric soil water content were simulated in different soil layers during the growth period of walnut. The results showed that when irrigation times were 7, and irrigation quota reached 2100 m3/hm2(expect spring irrigation and winter irrigation), the growth needs of walnut were better satisfied. |
PDF Full Text Request