| In Loess Plateau areas, dry and varied climatic condition was the main reason that resulted in the instability of soil moisture in surface layer. And because of the bad soil pedality and pore continuousness, the water in soil deep layers was difficult to supplement for that in surface layer. So, soil moisture of surface layer varied commonly and strongly. But so far as, people had paid less attention to this phenomenon. In view of improving the efficiency of fertilizer, we paid more attention to the effect of water dynamic process and strength on nutrient availability. In this research, by model test, four kinds of agricultural soils were studied, concerning about the effect of drying-wetting alternation and temperature on potassium availability, ions' diffusion in soils under different levels of water content, and the distribution coefficient of potassium between solution and soil phases. The main aim was, in theory, revealing the spatial relationship between water and nutrient and supplements the coupling effect, in practice, improving efficiency of water and fertilizer and increasing agriculture production.Results were showed as following:1. The empirical equation W=ASB was used to fit water holding capacity of four kinds of agricultural soils in loess Plateau. Soil water holding capacity and unavailable water content increased as soil texture became clayed. Available water content in Loam was higher than those in sandy soil and clayed soil. Under the same soil moisture suction, water holding quantity in soils from high to low in turn was Lou soil, Hei-lu soil, Loessial soil and Aeolian-sandy soil. Soil texture was an important factor affecting water-holding availability.2. Soil water regime affected the potassium availability in soils. Under applying K 200mg/kg, K fixation capacity of four soils strengthened with drying and wetting cycle and temperature increasing, so, the availability weakened. In general, capacities of fixing potassium of soils in turns were: Heir lu soil>Lou soil>Loessial soil>Aeolian sandy soil. The first time of drying and wetting cycle gave the most influence to total quantity of fixed potassium, and with cycles increasing, it's influence became weaker. With temperature increasing, potassium fixation capacity became stronger, and the effects varied among four kinds of soils.3. Equilibrium distribution of an ion between soil solution and solid phase was described by a distribution coefficient, K. The K was a ratio of Cs and C1 and a conditional equilibrium constant, which Cs and C\ were quantity of K in solid and solution phase respectively. As soil suction increasing, C1 increased and Cs decreased, then K decreased. When water suction approached 1.5 105Pa, K almost equaled a constant and there was relatively much amount of nutrient that could be used by crops easily. With soil becoming dried, more available K was fixed. K had closely relationship with O.M., CEC, clay content, and physical clay content.4. On soil profile, the distribution of KC1 applied at soil surface could be described by equations of C = a+blnz, where C was the concentration of the diffusing ion (mg/kg) of soil, z the soil depth, a and b simulated parameters. With diffusion time prolonged, ion's diffusion front went far and far from soil surface.5. Soil water content was a more important factor affecting the ion's diffusion. At the same temperature(25), soil bulk density(1.3g/cm3) and concentration of applied ions(0.014g/cm ), the value of chlorine diffusion coefficient (Dei) increased linearly with water content, and that of potassium (DK) increased exponentially or power-lawly. As diffusing time prolonged, the value of DCI became higher but DK lower.6. The tortuosity factor (f) was an important geometric parameter, which affected ion's diffusion and varied at different levels of water content. Equation of f=a+blnW was very fitful to describe the relationship of f and W(%).7. DCI had significant positive correlations with CEC, clay content, and physical clay content. A... |
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