Study On The Spatiotemporal Evolution Characteristics And Influencing Factors Of Soil Fertility In Agricultural Land

In modern agricultural production,with the changes of land use,fertilization,and management measures,soil fertility has changed significantly.Moreover,soil fertility conditions are also quite different due to factors such as soil type,topography,climate,and biology.Therefore,studying the changes of agricultural land soil fertility and finding out their driving factors has practical and long-term significance for the sustainable use of soil resources.This study took Boxing County as the research area,soil p H,organic matter,alkali-hydrolyzable nitrogen,available phosphorus,available potassium and other fertility data were collected from 2007 to 2020.Classical statistics and geostatistics methods were used to study its nearly fourteenth the content level,spatial variation characteristics and spatial distribution changes in the entire study area over the past years;on this basis,the comprehensive soil fertility index method is used to calculate the comprehensive soil fertility index,and its temporal and spatial changes are discussed,and geostatistical methods are used to preliminarily judge the impact the various indicators of soil fertility and the factors affecting the comprehensive level of soil fertility.At the same time,the natural and socio-economic data of each period in the study area were investigated and collected,and structural factors（soil type,soil texture,meteorological factors,soil salinity）and the influence of random factors（crop planting type,soil environmental quality,land use change,fertilizer application,etc.）on soil fertility.The main conclusions of the study are as follows:（1）Analyzed in terms of time,various soil fertility indexes have changed in different degrees in the past 14 years.The soil p H is showing a rising trend.By 2020,the soil p H value of the entire study area greater than 7.90,and showing an alkaline level.The average content of soil organic matter was maintained at around 15.2 g·kg^-1before 2013,and its average content was around 17.5 g·kg^-1 from 2014 onwards,and the content of soil organic matter in the entire study area has slightly increased.The average content of soil alkali-hydrolyzable nitrogen and available phosphorus decreased by one grade,the alkali-hydrolyzable nitrogen decreased from the upper-middle level to the lower-middle level,and the level of available phosphorus decreased from the rich level to the rich level.The two showed volatile changes in the early stage.The fluctuation range is relatively large,and it has shown a downward trend in the past five years.The average content of quick-acting potassium has not changed much in the first five years,remaining at around 160mg·kg^-1.It has continued to rise since 2014,with a large increase,one or two levels before and after,from the upper level to the rich level.And extremely rich level.The comprehensive level of soil fertility presents different grades of changes.The agricultural land at the first level continues to decrease,and the agricultural land at the second level continues to increase.（2）The change of soil fertility is weakened by the influence of natural factors and strengthened by the influence of man-made activities.As time goes by,soil fertility shows obvious regularity in space,and the distribution of plots of different grades becomes more distinct and concentrated.In the early stage,the soil fertility indexes and comprehensive fertility levels of different grades were distributed in patches throughout the study area;in the middle stage,it gradually appeared as the central region>southern region>northern region;in the later stage,the overall performance was that the western region was significantly higher than the eastern region.Regionally,the differences in the same region all show a gradual decrease,and they are developing towards uniformity,indicating that the regional soil nutrients tend to be consistent under the effects and influence of human activities;structurally,the spatial structure variation is weakened,and the random variation increases.（3）Random factors and structural factors affect soil fertility together.Soil fertility is gradually weakened by the influence of structural factors,and continuously enhanced by the influence of random factors.Comparing the land use status maps in 2007 and2020,it is found that the most obvious change in land use is the conversion of agricultural land to residential land,followed by the conversion of saline land to agricultural land.When agricultural land is converted to residential land,soil fertility drops by one level,and saline land is converted to residential land.Soil fertility has increased after agricultural land.In the past 14 years,the fertilization in the study area mainly has the problem that the application ratio of heavy chemical fertilizers,light organic fertilizers,and nitrogen fertilizers is significantly higher than that of potassium fertilizers and phosphate fertilizers,and the total fertilization rate is relatively high.The change law of soil available nutrients is basically consistent with the change law of fertilizer application.It can be seen that fertilization caused the main reason for the change of soil available nutrient content in the study area.Correlation analysis shows that soil salinity only has a significant negative correlation with soil p H,and has no obvious correlation with other soil nutrients.Among meteorological factors,precipitation and light only have a significant negative correlation with alkali hydrolyzed nitrogen,and temperature and there is a significant positive correlation between p H and organic matter.One-way analysis of variance showed that the influence of soil type and soil texture on soil organic matter,available nitrogen,available phosphorus,and available potassium has gradually decreased in the past fourteen years.It further shows that with the increase of time,soil fertility is deepened by the influence of human factors.Therefore,in the future agricultural production,we should vigorously promote soil testing and formula fertilization,and guide farmers to scientifically balance fertilization.In the process of agricultural soil nutrient management,we should pay attention to the application of organic fertilizers,appropriately control the input of chemical fertilizers.