Study Of Precise Control Of Soil Moisture And Its Applications

The research attempted to solve some theoretical and application-related problems in precise control of soil moisture. Soil moisture is precise controlled by controlling the water supply pressure at negative hydraulic head .The main results are as following:1. The principle and operating process of negative hydraulic head instrument were introduced. We offered a new way to control soil moisture in the experiment of soil science.2. Relationship between soil electric conductivity and soil matric suction was used to estimate soil air entry value. Glass Funnel with porous ceramic plate provided in this paper was identified as the method for the measurement of soil bubbling point. Air entry value and bubbling point of three profile layers during desorption were measured: Air entry value of Ap horizon was 13.4hPa , the bubbling point was 58.8hPa. Air entry value and bubbling point of AB horizon were 26.0hPa and 41.2hPa respectively. Air entry value and bubbling point of Ab horizon were 4.5hPa and 60.8hPa respectively. The measured results show that the air entry value and bubbling point are two concepts with different values.3. Negative hydraulic head irrigation was introduced. The instrument works well in field. The problem of homogeneity irrigation was answered through the experiments of soil moisture and wheat water content during growing season .4. Principle of negative hydraulic head and multi-pore materials were used to put forward a new setup and method for the measurement of soil-water characteristic curve. Both adsorption curve and desorption curve can be measured using the setup. The soil water characteristic curves of four different soil samples were measured using the method .The setup can measure the pressure range from 0 to–800hPa and it can be used for both disturbed and undisturbed soil.5. The influence of four non-surface profile layers (AB,Ab,Bk,Bg)on growth of crop root system and nutrient adsorption were studied using Chinese cabbage (Jing lv 2) with different fertilizer treatments using pot cultivation. Our experimental results suggest that sub-surface soil layers are not obstacle to crop growth, supplement of nitrogen and phosphorus and proper tillage and irrigation will help to improve the productivity of eroded soil. Long time of natural restoration of soil productivity is not needed.