| Scientific management of soil nutrients and rational use of fertilizer are strategic issues affecting sustainability of Chinese agriculture. Soil nutrients not only have spatial variability, but also change with the time. With the rapid development of agriculture in Zhejiang province, the management of soil nutrients in Hangzhou-Jiaxing-Huzhou (HJH) water-net plain is directly connected with the crop yield and agricultural non-point source pollution. So, understanding the spatial and temporal variability of soil nutrients in paddy field is the foundation of precision agriculture management. There has been growing interest in the study on spatial variation of soil properties in dry land using geostatistics since 1970s, and geostatistics has also been well developed and is proved successful in characterizing the soil variation. While many studies have been carried out at a small scale, relatively few have been done at large scale, especially on paddy field. Geostatistics and GIS were used in this study to analysize the spatial and temporal variability of soil nutrients in paddy field and their mechanism under three different scales of HJH Plain (1:250000), Pinghu county (1:50000) and Tongxin test plot area (1:2000), meanwhile, the regionalized management was brought forward in this study. The main results obtained are summarized as follows:1. Spatio-temporal variability of soil nutrients in paddy field in HJH PlainThe contents of soil organic matter (SOM), total nitrogen (TN) and available phosphorus (AP) in HJH Plain increased from 1982 to 2001, whereas, that of AK decreased dramatically. This change was in consistent with the fertilization structure, excess application of N and less application of K fertilizer in this region.The Household Responsibility System initiated at the end of 1970s in China has brought a profound change to its rural economy. Farmland was allocated to each peasant household on the basis of family size, and farmers have been given the right to till the contracted land. The township governments allow the farmers of each household to make all the decisions about production. The shift from the collective farming system to individual family farms has changedthe type of land utilization and management. After long different land management, the content of SOM and TN has become more uniform than before. The CV value for SOM and TN was all decreased during the past 20 years, however, that for AP and AK increased.Semivariograms of the soil nutrients in HJH Plain in 2001 displayed that they were all moderately spatially dependent, which illuminated that the long history of soil management of the field had weakened the spatial variability determined by the characteristics of the soil properties. The spatial and temporal distribution maps of SOM, TN, AP and AK further explained the patterns of their change during the past 20 years, which lay the foundation of agricultural management in the future. There was strong spatial variability for soil available Zn and Cu under long distance. Based on the classification of soil nutrients in Zhejiang Province, regionalized management of soil nutrients in HJH Plain was analyzed. And the SOM and AP were divided into three regions and two regions for TN, AK, available Zn and Cu. The mode of regionalized management could aid for the precision agricultural management.2. Spatio-temporal variability of soil nutrients in Pinghu CountyThe spatio-temporal variability of SOM and nutrients in paddy field induced by land management change was apparent. Over longer history of land management of Household Responsibility System, the spatial variability of soil properties was determined by the characteristics of the soil properties and the history of soil management of the field. It is worthy to note that the fitted r~2 values for soil AP and AK in 2002 were very small, both semivariograms showed pure nugget effect with weak spatial dependence. This illuminated that the spatial variance between farmers owing to different land management was covered at large scale. These results ind...
|
PDF Full Text Request