Spatial And Temporal Variation Of Soil Available Potassium In The Field Of Wheat-rice Double Cropping

The spatial-temporal variation of the field of wheat-rice double cropping has been analyzed for Yizheng city of Jiangsu province by making good use of four phases of soil general investigation data from 1982 to 2005 as a case study, using Geo-statistics methods and GIS technique to analyze the soil available potassium level, the spatial-temporal variation characteristic and the spatial distribution. Furthermore, discussing the various geomorphologic types, various soil types, various soil parent materials and so on, which have the influence on the temporal-spatial heterogeneity of soil available potassium, finally, analyzing to change the main reasons and the corresponding countermeasure. The results described as follows:The findings discovered that the available potassium average content in 1982 were lower than in 1994 from 91.20 mg/kg to 73.63 mg/kg and kept rising gradually to 91.62 mg/kg in 2005, the content of the available potassium between the year of 1982 and 2005 was almost the same.The spatial distribution variations are found in different years. All theoretical model conforms to the exponential model ,moreover, the spatial distribution also had the obvious change tendency, the range of the available potassium was from 20.28 km in 1982 to 8.32 km in 1994, increased to 24.18 km in 2000 and reduced to 8.18 km in 2005; the ratio of nugget to sill of available potassium changed from 48.48% to 74.33%, which was found that spatial heterogeneity of available potassium showed moderate spatial auto-correlation in different years, however, the degree of the spatial heterogeneity in 1994 and in 2005 were higher than in 1982 and in 2000.According to the soil available potassium distribution and the appraisal rank analyzed that the content of available potassium in plain area high sandy soil were lower than in the hilly area, moreover ,the distribution of the soil available potassium in Yizheng city in 1994 have a obvious bulk reduction tendency to the second soil general survey in 1982, but the soil available potassium distribution had a large scale enhancement in 2005, which achieved 1982 the average level but the growth scope distributed non-uniformity. Analysis the content of soil available potassium in 2005 showed that 74.76% area had achieved the Ministry of Agriculture soil available potassium gradeâ…¡level standard, its distribution and the mean value about 90mg/kg which are under gradeâ…¡Level standard.Compared the data of slow-release potassium in Second National Soil Survey in 1982 with data in 2005,the findings discovered that the content of the slow-release potassium in 1982 was significantly higher than that in 2005. The average content of which changed from 612.27 mg/kg to 541.30 mg/kg, with the whole dropped 70.97mg/kg, the soil potassium stock continues to the bad condition all the same; Significant difference for soil properties are found in different subgroup soils showed that slow-release potassium in kinds of the subgroup soils reduced in different degree except for the gley paddy soils and submergic paddy soils, and scope of the average content of the slow-release potassium reduced approximately from 40 mg/kg to 85 mg/kg.Compared with the available potassium data of various geomorphologic types indicated that the content of available potassium in the area of hill and mesa were obvious higher than that in the areas of floodplain and plain. Significant difference for soil properties are found in different subgroup soils which the content of the available potassium rank in the following order: lithosols and yellow brown soil> various subgroup paddy soil> grey chao soil. Similar method are presented in different soil parent materials too, which showed that new alluvial deposit soil from Yangtze River and Xiashu Loess were higher than alluvial deposit soil from Yangtze River. In addition, statistics are performed to determine the content of the available potassium in different soil texture. The result followed that medium loam soil, heavy loamy soil and light clay soil were higher than light loam soil.Based on the data of the survey and stationary monitoring of soil fertility, grain yields, fertilizer investigation and so on from 1980 to 2005, and make use of fertilizer investment situation investigation of 182 peasants in Yizheng region, which were concluded that the improvement of the available potassium in soil was mainly contributed to the more application of fertilizers, the changes of tillage, government policy, crop system and soil management.The critical value of soil available potassium in this area was 80 mg/kg application of potash fertilizer was effective, when soil available potassium was less than 120 mg/kg application of potash fertilizer was not effective, but this measure can also increase production.It is essential to consider the spatial variability of soil nutrients in order to balance sampling cost and accuracy. In this study, the rational sampling quantity could be determined by using Stratified and Rational Distributed Sampling and using Cochran formula. The result showed that the rational sampling quantity for available potassium in various counties which have obvious otherness would be 178 under 95% significant level and 5% relative error, which was better than Cochran formula that the rational sampling quantity for available potassium would be 217 under 95% significant level and 5% relative error. According to spatial variability characteristic of different soil properties, it should make tradition statistics and geo-statistics together to determine the sampling plan in actual sampling. Therefore, the mode of regionalized management, determined the synchronism sample work and enhanced the efficiency could aid for the precision agricultural management.