Spatial Variability Of Soil Nutrients And Evaluation Of Farmland Productivity In Yulin City Based On GIS

This study is based on the data of farmland sampling points in the counties of yulin city,shaanxi province,with the support of soil testing formula fertilization project,usingthe traditional statistical,geostatistics combined with GIS technology to analyze soil nutrient spatial structure,spatial distribution and the distribution of the farmland productivity level in Yulin city.The results of the study are as following:(1)The content of available nitrogen and available phosphorus in soil was between 0.20~100.30 g/kg and 0.10~47.10 mg/kg,with an average content of 36.16 g/kg and 8.73 mg/kg,all in the 6th grade of soil fertility index classification standard.Soil available potassium content is between 14.00~281.00 mg/kg,the average level of 110.64 mg/kg,in the 4th grade of soil fertility index classification standard.The content of soil organic matter was 0.10~23.70 g/kg,and the average content was 7.13 g/kg,which was the 8th grade of soil fertility index grading standard.The pH value is between 5.00 and 10.80,with an average value of8.31,which meets the 4th grade.The variation coefficient of pH in the study area was the smallest,5.17%,which was the weak variability.The variation coefficient of soil available nitrogen,available phosphorus,available potassium and organic matter was between 42%and 83%,all of which were of moderate variation,and there was a significant correlation between the five nutrient elements(p<0.01).(2)The optimal theoretical model of soil available nitrogen,organic matter,available phosphorus and available potassium in the study area is exponential model,and the optimal theoretical model of pH value is spherical model.The nugget coefficients of the five soil nutrient elements were between 0.441 and 0.685,which were of moderate spatial correlation.The total dimension of the five soil nutrients is relatively high,between 1.922 and1.979,and the spatial heterogeneity is as follows:available nitrogen>available potassium>effective phosphorus>organic matter>pH.The spatial autocorrelation of the five soil nutrients was significant in Yulin area(p<0.01),and the Z value was greater than 2.58,and spatial clustering feature is obvious.(3)The available nitrogen of soil in the researched areas has the characteristics of remarkable spatial distribution,which were rich in the central and southwest region,in the southeast region weakly.Soil available phosphorus in the spatial distribution pattern were high in the north and low in the south generally,and the overall available phosphorus content is low.The range of available potassium was large,with an average content of 114mg/kg(level6),the overall level was high.The organic matter is generally presented mission shapes in the space structure,and the organic matter content is low in the northeast to the southwest.The soil pH value is generally alkaline,and presented mission shapes the spatial pattern.(4)Different soil types have a certain effect on the content distribution of soil nutrients.On the whole,soil nutrient content:aeolian sandy soil>alluvial soil>loessal soil,soil type has a significant effect on soil nutrient content.The soil components in the study area shows significant correlated with factors like altitude and fluctuation degree on 0.01 level.(5)The total farmland area of the researched region is 10943.68km~2.The area ration of grade 1 is 3.41%,6.33%for Grade2,13.48%for Grade3,34.82%for Grade4,29.99%for Grade 5,8.54%for Grade 6,and 3.43%for Grade 7.The first level land were mainly distributed in the floodplain and terrace areas along the estuary of Yulin city.The second grade land were mainly distributed in Dingbian county,except Wubu county and Zizhou county,the other counties have sporadic distribution.The grade 3 land were mainly distributed in Jingbian county and Dingbian county,Wubu county has no distribution,and the remaining counties have a small distribution.The grade 4 land were distributed in all counties,and the area is widely distributed in the loess and hilly cultivated land areas in Dingbian county,Qingjian county,Zizhou county,Jiaxian county,Mizhi county and Suide county.The grade 5 land were distributed in the loess gully and hilly areas of Yuyang district and Hengshan district.The grade 6 and grade 7 land were mainly distributed in the marginal areas of the loess gully hills along the district of Wubu county-Yuyang district-shenmu city-Fugu county.