黄土高原南麓县域耕地土壤速效养分时空变异

Abstract

Soil available nutrients play important roles in ensuring high,stable yields and avoiding water eutrophication.In this study,the spatiotemporal variation of soil available nitrogen(AN),phosphorus(AP) and potassium(AK) was studied in Heyang County of Shaanxi Province,an ecologically vulnerable area at the south Loess Plateau.Two sets of data were used for analysis in this study,in which 545 and 618 soil samples data were from the second national soil survey in 1983,and Shannxi Province arable land soil fertility survey in 2006,respectively.Prior to data analysis,outliers were identified and removed.Logarithmic and BOX-COX transformations of data were performed to obtain normality distribution of variables.Data were analyzed with spatial autocorrelation,semi-variance function and fractal dimension analysis.Factors affecting soil nutrient change were identified using Kriging interpolation and zonal statistics. The results showed that mean concentrations of arable soil AN,AP and AK were 35.4,8.2,and 195 mg/kg in 1983,respectively;whereas their average contents in 2006 were 61.5,15.8,and 196 mg/kg,respectively.The contents of soil AN and AP were significantly increased from 1982 to 2006 by 26.2(74.0%) and 7.6(92.7%) mg/kg,respectively.It was found that there was significant difference between soil available nutrient contents in 1983 and those in 2006 based on the Levene′s equality of variance test. Spatial autocorrelation analysis showed that the Moran′s I values of AN,AP and AK in the two time points all showed spatial cluster at 0.01 significance levels.Soil available nutrients in 1983 had higher Moran′s I values,indicating their stronger spatial structure.In semi-variance function and fractal dimension(FD) analysis,AN,AP and AK contents in 2006 had shorter spatial correlation distance and higher fractal dimension values,suggesting that soil available nutrients in 2006 exhibited weaker spatial structure and self-similarity.Thus,results obtained from analysis with three methods confirmed their effectiveness. The spatial patterns of soil available nutrients in 1983 and 2006 were analyzed with kriging interpolation and raster computing in ArcGIS.It was found that soil AN and AP contents in most study areas showed varying degree of increase in the past 23 years.In contrast,soil AK content decreased in 59.65% of arable land during this period.The relationships were analyzed between soil nutrient changes and land use type,fertilizer application,geomorphic type,soil type and so on.It was found that soil available nutrient changes were significantly affected by these factors.Among others,excessive N and P fertilizer use and land use change were the main reasons for soil AN and AP increase.The decrease of soil AK was due primarily to the shortage of K fertilizer.