| What scientific irrigation is going to solve is not simply the problem of water saving, more importantly, the scientific distribution of soil moisture around the plant roots. Based on the water conducting medium material, non-pressure infiltration irrigation is a new kind of water-saving irrigation technique, which is specifically aiming at desertification areas. The key water conducting material could automatically transport water to soil by water potential difference, and it could control and keep the soil moisture near the irrigation emitter in a reasonable range. Much research has been conducted on the key water conducting material, and lots of results are obtained. And the field test and practical application have also gotten good effects. The focus of this paper is the dynamic model of the key water conducting material and the water conducting mechanism, in order to provide theoretical basis for further application of water conducting material.By analysing the performances of water absorption and release, the portion of polyacrylamide and montmorillonite was set as 1:4. The infiltration irrigation material’s water kinetics equation based on finite difference method was derived. Combined with infrared spectrum analyzer, X-ray diffraction, thermal analysis and environmental scanning electron microscopy, the water conduction mechanism was researched. Major researching results are as follows:1. According to the structural characteristics of the material, the one dimensional horizontal movement equation of water based on Darcy Formula was built. In order to determine the diffusion rate, the water characteristic curve and diffusivity curve were determined and calculated by high speed centrifuge experiment and Mariotte Bottle experiment. To solve the equation, four methods as Laplasse transform method、 Philip method、Parlange method and the finite difference method were used and resulted in 4 models. By studying the 10 min and 60 min curves, it was found that the curves of finite difference method matched best with actual data, while others didn’t. In order to study the relationship of cumulative infiltration capacity and time, finite difference method was used to build the infiltration capacity model. At the same time, the Green-Ampt model was used for comparation. The results showed that the model of finite difference method matched well with actual data, while the model of Green-Ampt made a great difference. Comparisons between water transportation model of finite difference method and measured values of infiltration irrigation system showed that theoretical equation matched well with measured values, which proved the accuracy of the theoretical model.2. By studying the i~t and i~θe curves, it was found that montmorillonite-based infiltration irrigation water conduction material could automatically adjust the water conducting speed. When soil moisture was low, infiltration irrigation materials could quickly transport water to the soil. When soil moisture rose, the materials could reduce the rate of water conductivity to reduce water waste. This was consistent with the results of laboratory and field experiments, and it also proved the accuracy of the model.3. The unification of the experimental results and the dynamic model was based on the coordination of the internal change of the water conducting material and the water conducting process. Using advanced instruments, the water conducting process was studied. The results showed that water transporting mainly depended on the interaction between polyacrylamide and montmorillonite. The water conducting process could be divided into three stages. At the beginning stage, polyacrylamide was dry and its polymer long chain shrank. The montmorillonite particulates adhered uniformly in polyacrylamide’s network structure by forming hydrogen bonds with its acylaminos. The mutually bridged montmorillonite particulates formed the water transport channel, so the water conductivity speed was fast. With water conducting, polyacrylamide began to absorb water. In the process of polyacrylamide water-absorbing swelling, the montmorillonite particulates adhered to polyacrylamide moved with its network structure. The distance between the particulates gradually enlarged until they were divided. In this stage, the water was transmitted by montmorillonite and polyacrylamide simultaneously, and the water conduction rate decreased very quickly. After the montmorillonite particles were completely separated by water-absorbing swelling polyacrylamide, the water conducting channels were completely cut off and water could only be transmitted through polyacrylamide. So the slow and steady water transfer stage came. From the view of internal structure of material, all the three stages appeared alternately in the actual water conducting process. The water potential difference of both sides of the water conducting material was large when soil moisture was low. Water was transmitted to the soil quickly through the water conduction material. Water potential gradient along the direction of water transmission was caused by the inconsistency of polyacrylamide water-absorbing swelling, which made sure the rapid water transmission to the soil. When soil moisture was high, the water potential difference along the direction of water transmission reduced, so the water transmitting rate decreased. So the infiltration irrigation system could automatically adjust the water transmitting rate with the soil moisture.4. Based on the unity of the water dynamics equations、water penetration tests and material microstructure changes, the indoor sandbox test and Inner Mongolia desert field test was conducted. The results showed that non-pressure infiltration irrigation not only can save more water than drip irrigation. And it could also adjust the water conducting speed according to the external soil moisture. Field test showed that inoculation rate of Cistanche could significantly increase from 19% to 80% by using non-pressure infiltration irrigation. Non-pressure infiltration irrigation technology gave the inoculation of Cistanche a great progress, and it also proved the correctness of the non-pressure infiltration irrigation theory.Above all, based on the research findings of the water conducting equation、cumulative infiltration equation and the material’s internal microstructure changes with the water conducting process, the water dynamic model was proved to be correct. And the research findings have important guiding significances on the actual production. |
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