Analyzing Spatial Variability Of Soil Fertility And Identifying Fertilization Management Zones

Avoiding soil degradation and improving crop productivity could be achieved by performing sustainable soil nutrient management with an appropriate understanding spatial variability of soil properties.Knowledge concerned to spatial variation of soil resources and soil MZs(Management zones)in Sichuan Basin is still limited,leading to a traditional management,i.e.similay management of its soil fertility over wide areas.The neglected spatial heterogeneity of soil properties could lead to high frequency of soil degradation and environmental depletion because of the under and over applying of the agricultural inputs.Thus,this research was first carried out to to evaluate the spatial distribution of some soil properties,and then identify the studied areas into MZs for performing site-specific managing practices.Three sites in three counties were selected to study the spatial variability of soil fertility in Sichuan Basin,in which the soil samples were collected at the field-scale from the agricultural field located in Jianyang,while the samplings were collected at the countyscale in each of Lezhi and Yanjiang.As a consequence,in sum 100 soil samples were collected from Jianyang,whereas 2754 soil samples were taken from Lezhi,and 610 ones from Yanjiang,respectively.Soil samples were determined for pH,the contents of organic matter(OM),total nitrogen(TN),available phosphorous(AP),available nitrogen(AN)and available potassium(AK),as well as soil C:N ratio,in each of Lezhi and Yanjiang.While the soil samples in Jianyang were analyzed for pH,available nitrogen(AN),available phosphorus(AP),available potassium(AK),soil organic carbon(SOC),total nitrogen(TN)and total phosphorous(TP),whereas C:N,C:P and N:P ratios were calculated.Coefficients of variation(CVs)for the studied attributes were extremely varied from low to moderate in the three studied areas in,which ranged from(2.82%)to moderate(63.21%)in Lezhi,from low(11.79%)to moderate(79.08%)in Yanjiang and from low(1.132%)to moderate(45.748%)in Jianyang.By performing ordinary kriging analysis,the fitted variograms revealed different spatial distribution patterns for the studied variables in the three sites,with spatial dependence varied from weak to strong in each of Lezhi and Jianyang,and from weak to moderate in Yanjiang.Principle component analysis(PCA)and fuzzy kclustering were used together to delineate the heterogeneous management zones.In Lezhi only two principle components(PCs)had eigen values>1 and contributed to 70.5%of the total variance,while three PCs with eigen values>1 dominated 76.3%of the total variance in Yanjiang,while four PCs with eigen values more than 1 dominated 84.44%of the total variance in Jianyang.The two criteria of quantitative estimation modified partition entropy(MPE)and fuzziness performance index(FPI)were performed to select the optimal number of MZs,in which each of the studied areas located in Lezhi and Jianyang was divided into three MZs,while the one located in Yanjiang was separated into four MZs.Analyze of variance(ANOVA)test revealed the significant variation of soil fertility over the delineated MZs in each of the three sites.In conclusion,due to the high spatial variability of the measured soil properties over the three fields and the high heterogeneity of soil fertility among the delineated management zones in each of the studied areas,this study recommended to use the delineated MZs for site specific managing,to avoid soil and environmental degradation,and to achieve the maximum crop yield productivity in the both sites.