Study On Leakage Loss And Utilization Of Potassium In Purple Soil

Potassium is one of the three necessary elements for plants. There are important effects on increasing yields, improving quality, intensifying stress resistance of crops by reasonable fertilization of potassium. Our country is short of potassium resources. The 90 percent of potassium fertilizer depend on important. And the areas of farmlands which are short of potassium are increasing. How to increase potassium utilization and decrease the loss of it attract the commonly attention of people. The loss of soil potassium includes runoff loss and leakage loss. Researches about the runoff loss are excessive. The leakage loss of potassium was studied in latosol and red soil. While research about the leakage loss of potassium in purple soil with rice- wheat rotation system is insufficient. In order to provide scientific foundation for the reasonable application of potassium, and reduce loss of it in rice- wheat rotation system. This paper studies the leakage leaching of potassium in rice-wheat rotation system in three types of purple soil by using nutrient percolation pond facilities. It also analysises the effects of different potassium rates on yield, quality and potassium utilization of rice and wheat. The main results are as follows:In the growth stage of wheat, the leakage loss concentration of potassium declined with the growth of wheat. In the early 70 days, the leakage loss concentration of potassium was high, then gradually reduced. The change regulation about the leakage loss concentration of potassium in neutra soil, acidic soil and calcareous soil were the same. In the growth stage of wheat, the leakage loss concentration of potassium was in the range of 3.0kg/hm~2～8.8kg/hm~2, the everage was 5.1kg/hm~2. Soil properties affected the leakage loss of potassium. The leakage loss concentration of potassium were 3.7kg/hm~2, 3.4 kg/hm~2 and 8.4kg/hm~2 on average in acidic purple soil, in neutral purple soil and in calcareous purple soil , respectively. The leakage loss concentration of potassium was higher in acidic purple soil than in neutral and calcareous purple soil, the increase degree was 147%, 127%, respectively. The application of potassium in neutral and calcareous purple soil increased the leakage loss concentration of potassium, the increase degree were 22.5% and 15.5%, while in acidic purple soil, and the degree was 5%. It indicated that the leakage loss of potassium was mainly from soil in acidic purple soil. In neutral purple soil, as comparison to the treatment with the aplication of potassium by base fertilizer(100%), the aplication of potassium with base fertilizer (50%) +topdressing(50%) increased the leakage loss of potassium, and the increase degree was 19%. It indicated that the application of potassium with topdressing could conduce the loss of potassium easily. The reason will be studied in the future.In the three types of purple soil, the potassium leaching dynamic taked the similar shape of wave-like changes. The highest concentration of leakage loss appeared on the 5th day after transplanting, then decreased, on the 70th day existed peak of leaching loss again. The loss content of potassium in rice growth season was 2 times higher than in wheat growth season, and the scope of change was 4.2～22.28kg/hm~2, on average of 11.02kg/hm~2. In the rice growth season, the leakage loss content of potassium in different soils was different. The absorption ability of potassium in acidic purple soil was weak; the leakage loss content of potassium was higher than neutral and calcareous soils. With the potassium rate of 0,90,180kg/hm~2, the leakage loss content of potassium in acidic soil were 4.6,3.6 and 3.5 times higher than in calcareous soil, and 3.2,2.8 and 2.6 times higher than in neutral soil. The leakage loss content increased as the application of potassium rate increased. As comparison to the treatment with no application of potassium, the treatment with potassium rate of 90 kg/hm~2 and 180 kg/hm~2 increased the leakage loss content from 30～52% in calcareous purple soil, 15～39% in neutral purple soil, and 14% in acidic purple soil. Soil characters, fertilization and moisture (rainfall and irrigation) all influenced the migration and leaching loss of potassium in soil.With the application of potassium increased, the yield of grain, leaf and stem about wheat all increased significantly. The average yield of grain was 3920.8kg/hm~2 in three types of purple soil with application of potassium. While with no application of potassium, the average yield of grain was 2984.9kg/hm~2, and the increase degree was 31.4%. In the neutral soil, the yield of wheat grain was higher than in calcareous and acidic soil. Considered either from the effect of potassium on yield, quality or leakage loss content, the wheat planted in neutral purple soil got the best effect, the calcareous soil got the second, and the neutral purple soil got the worst. The treatment with high rate of potassium (180 kg/hm~2) decreased the yield and starch content of wheat, and the effect was eapecially obvious in neutral soil. It showed that the high application of potassium was not the best fertilization measure, in the purple soil the reasonable application rate of potassium was 90 kg/hm~2. As the application of potassium increased, the content of potassium in the grain of wheat increased, and the increase degree was 23.9% as comparison to the treatment with no application of potassium. With high application of potassium in calcareous soil, the content and the absorption of potassium were the highest; the next in order was in neutral soil. In the wheat growth season, the recovery of potassium fertilizer was in the scope of 11.8%～21.6% in three types of purple soil. And the utilization was in the order of neutral soil>acidic soil>calcareous soil. In calcareous and acidic soil, as the application of potassium increased, the content of potassium decreased in the rice grain and it increased in rice straw, the increase degree was 21.2% as comparison to the treatment with no application of potassium. The absorption amount of potassium in the overground rice was the highest in neutral soil and it was the lost in calcareous soil. In the rice growth season, the recovery of potassium fertilizer was 32.2% on average in the three types of soil. The recovery of rice was higher 15 percent point than the recovery of wheatFrom potassium blance sheet in rice-wheat rotation system, the deficit amount of soil potassium was 148.8 kg/hm~2 annually with no application of potassium. The surplus and dificit of potassium was not significant in three types of soil under the potassium rate 180kg/hm~2. In neutral and acidic purple soil, the average deficit amount was 13.2 kg/hm~2, while in calcareous purple soil there was a little surplus. When the application of potassium fertilizer was 360kg/hm~2, there was surplus of potassium in the three types of soil. The surplus of potassium was 39.7%, 37.9% and 37.1% in the calcareous soil, neutral soil and acidic soil, so it raised the content of available potassium in soil.