| The soil potassium is the most important component of soil fertility and the main source of crop’s potassium nutrition. In recent years, with the increasing amount of nitrogen fertilizer and crop yield, gradually expand the area of soil potassium, the phenomenon was especially most prominent in rice-wheat or rice-rape rotation system in southern China. The soil potassium deficiency has become a limiting factor for grain yield, but the potassium fertilizer resources is shortage in China, therefore we need to find the effective supplementary means with potassium of soil except for chemical potassium. In addition to application of organic manure and straw returning are used to supplement potassium pools, improved tillage management is also an effective measure. The study in this thesis is based on a long term ridge-cultivation without tillage experiment located at Beibei District, Chongqing City, and it has lasted for 22 years. We use the long-term experiment combining with laboratory analysis method to research the potassium forms, the clay mineral composition and relative content, potassium fixation, release kinetics of non-exchangeable potassium, and potassium quantity-intensity relationship of the paddy soil in the different tillage methods and soil layer. The potassium supplying capacity of soil was comprehensively analysised and evaluated in the different tillage methods and soil layer. The objective is to provide the scientific basis for improving the ability of the soil potassium through improve tillage management and fully excavate the potential of soil K. The main results of the thesis are listed below:(1) After 22 years long-term cultivation, there were different degree of reduce with the available potassium, the slowly available potassium and total potassium on the basic of original soil for all of treatments and depth. In the 0-20 cm soil layer, there were smallest decline on the basic of original soil with the available potassium of conventional tillage, the slowly available potassium and total potassium of combing ridge with no-tillage. In the 20-40 cm soil layer, there were smallest decline on the basic of original soil with the available potassium and total potassium of conventional tillage, the slowly available potassium of flooded with no-tillage. In the monoculture system, the conventional tillage was more improved the available potassium, total potassium, and the slowly available potassium of the 0-20 cm soil layer than the flooded with no-tillage. In the rotation system, there were lowest with the slowly available potassium of plain culture with no-tillage, the available potassium and total potassium of plain culture with tillage in the 0-20 cm soil layer. There were lowest with the available potassium of tillage and ridge culture, the slowly available potassium of combing ridge with no-tillage, and total potassium of green manure with the 20-40 cm soil layer.The 20-40 cm soil layer was beneficial to maintain the potassium pools, because it was higher than the 0-20 cm soil layer.(2) After 22 years long-term cultivation, different farming methods to deal with soil K clay mineral composition without the influence, different treatment of soil and the different depth in the soil K clay mineral have illite, montmorillonite, kaolinite and vermiculite. The order of its contents was expressed as illite> montmorillonite> kaolinite> vermiculite. Correlation analysis showed that:the montmorillonite and kaolinite affected significantly illite content, with a correlation coefficient of r=-0.740 (P<0.01) and r=-0.573(P<0.05). In the 0-20 cm soil layer, the value of illite was decreased, but the value of montmorillonite was increased. It showed that:in the long-term paddy-upland rotation system, the illite had a lot of weathering and disintegration in the neutral purple soil clay, and accompanied by a large formation of montmorillonite. In the 20-40 cm soil layer, the value of montmorillonite was decreased except of tillage and ridge culture and paddy-upland rotation, but the value of illite was increased. It showed that:in the long-term paddy-upland rotation system, the increase of montmorillonite K fixation capacity lead to increase of illite.(3) After 22 years long-term cultivation, when the K application rate was 0.4 to 4.0 g·L-1, the amount of fixed K increased with the increase of K applied, but the K fixation rate decreased in different treatment of soil and the different depth. There were different degree of increase with the K fixation capacity on the basic of original soil for all of treatments and depth. Moreover, among them the plain culture with tillage in the 0-20 cm soil layer and the tillage and ridge culture had the highest increase amplitude in the 20-40 cm soil layer. Comparing with sole cropping, the K fixation capacity was relatively large with crop rotation. In the monoculture system, the K fixation capacity is insignificant for all of treatments. The relative content of clay minerals in soil is the decisive factor affecting the ability of K fixation. The K fixation capacity was also closely associated with the available K, SOM, and CEC in soil. The K fixation rate was respectively a significant negative correlation with the available K and a significant positive correlation with SOM or CEC. When the K application rate was 0.4 to 4.0 g·L-1, the available K was the main factor affecting the K fixation capacity in the 0-20 cm soil layer, but the K fixation capacity was influenced by the content of CEC in the 20-40 cm soil layer.(4) After 22 years long-term cultivation, the cumulative amount of non-exchangeable K released were larger within 49 h in different treatment of soil and the different depth. Then release decreased, and slowly stabilizing. In different soil layers, the cumulative amount of non-exchangeable K released of all treatments changed between 64.13 and 84.54 mg/kg. Compared with before the experiment, the amount of K released of conventional tillage in the 0-20 cm soil layer and flooded with no-tillage in the 20-40 cm soil layer was a slight increase on the basic of original soil, but there were different degree of decrease with other treatments. The falling range was maximal with the amount of K released of combing ridge with no-tillage in the 0-20 cm soil layer and green manure in the 20-40 cm soil layer, the value about 20%. In this study, the release of non-exchangeable K was simulated by four kinds of soil dynamics equations. The results showed that the parabolic diffusion equation was best, the first-order reaction equation was better, the zero-order reaction equation was poor, the elovich equation was worst. In different soil layers, the non-exchangeable K release rate (b) of the first-order reaction equation was significantly lower than the parabolic diffusion equation, but the intercept (a) of first-order reaction equation was significantly higher than the parabolic diffusion equation. The non-exchangeable K release rate was closely related to soil properties. The release rate was significantly positively correlated with the slowly available potassium and CEC.(5) The shape of these curves was similar on potassium quantity-intensity relationship in soil under the different tillage methods. There are constituted by the curved portion (AR is low) and the straight portion (AR is high). Compared with before the experiment, the slope of each treatment were higher than the original soil in different soil layers. This showed that there were different degrees of increase with buffering capacity of soil potassium on the basis of the original. Especially the combing ridge with no-tillage in the 0-20 cm soil layer and the tillage and ridge culture in the 20-40 cm soil layer produced the best effects on improving potassium buffering capacity and also was beneficial to maintain the potassium levels. These parameters supplying potassium were significantly influenced by different tillage methods. Compared with before the experiment, there were different degree of reduce with the soil potassium supplying intensity (ARoK), activity of potassium (KL), and potassium supplying capacity (-△K0) on the basic of original soil for all of treatments, but there were different degree of increase with the soil potassium potential buffering capacity (PBCK) and the value of exchange free energies (-△G) on the basic of original soil. In addition, the crop rotation was less than the sole cropping.In the monoculture system, the conventional tillage was more improved AR0K and -△K0 than the flooded with no-tillage, while the value of PBCK and -△G for the conventional tillage was lower than the flooded with no-tillage. This showed that the conventional tillage was better than the flooded with no-tillage for improving soil potassium supplying capacity. In the rotation system, no-tillage was better than the cultivation for improving soil potassium supplying capacity except paddy-upland rotation. These parameters supplying potassium were closely related to the available K, the organic matter, and the cation exchange capacity. The AR0K was respectively a significant positive correlation with the available K and a significant negative correlation with CEC. The PBCK was significant positive correlation with SOM and CEC. The-AG was respectively a significant positive correlation with CEC and a significant negative correlation with the available K. These potassium parameters (AR0K、-△K0、PBCK、-△G) combine with the available K, the slow release K and the total K, it can evaluate better the soil potassium supplying capacity. |
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