Effect Of Water Condition And Low-molecular Weight Organic Acids On Potassium Transformation In Red Soil And Yellow-cinnamon Soil

This research selected two paddy soils, red soil and yellow-cinnamon soil, which have a representative in south China. The indoor imitative culture experiment and dynamic test were carried out to research the dynamics of release, adsorption of potassium, the fixed quantity and released quantity of soil on the condition of K added or not under the influence of water condition and low-molecular organic acids. This paper provided a scientific basis on promoting the percentage of K used. The main results were as followed:1. Compared to the control, available K in red soil were increased significantly under two different constant humidities (25 % and 40 %), and showed an increasing trend with the time. But available K in yellow-cinnamon soil which did not change obviously was lower than that of control. There was no significant difference between the two constant humidity of 25 % and 40 % in same soil. The results showed that the water film thickness of soil particle surface could not be a controlling factor which effecting potassium availability in soils.2. Under the water conditions of alternate drying-wetting, available K in red soil did not change obviously, which in yellow-cinnamon soil increased gradually. With the increase of wet-dry cycles, the K fixation capacity of yellow-cinnamon soil decreased but increased in that of red soil. We believed that the clay group played an important role in promoting the release of inter-layer K of yellow-cinnamon soil in the drying process.3. The incubation experiment of LOAs indicated that LOAs accelerated the transformation of exchangeable K to water soluble K among all treatments.4. Available K have different variation tendency with different kinds of LOAs in red soil, and available K increased with the increment of LOAs among all treatments of yellow-cinnamon soil. It shows that LOAs could increase K⁺ adsorption by a increasing the surface charge on variable charge soil.5. At 25 mmol/kg level, the order of 1M HNO₃ extractable K in red soil was as follows: citric, malic>oxalic; there is no obvious changes were observed among all treatments in yellow-cinnamon soil. At 400 mmol/kg level, the 1M HNO₃ extractable K order of tested soil was oxalic>control>citric, malic. Therefore, it is significant to make a further research the effect of LOAs on 1M HNO₃ extractable K of soil.6. Kinetics experiments indicate that LOAs accelerate K release from the soils obviously, and K release will show an accumulate tendency with the time. Elovich, Power function, Two-constant equation fit the experimental data very well and Two-constant equation could describe K release best.7. At 0.1 mmol/L level, organic acids showed inhibitory effect on potassium adsorption, and a negative adsorption was observed in the red soil treated with 0.1 mmol/L oxalic acid, the K adsorption capacity of two soils was in the order of oxalic>citric>malic. At 0.1 mmol/L level, the K adsorption of red soil was lower than that of control, while higher in yellow-cinnamon soil. Comparing with two eluate concentrations of K, we can see that the higher eluate concentrations of K, the faster adsorption process is.8. Results show that the velocity of adsorption reaction has a good linear relationship with lnt, reaching significant or very significant level. Comparison of the models using the coefficient of determination (r²) and the standard error of the estimate (SE) indicated that Two-constant equation overall displayed the best fit.