Spatial Interpolation and Sample Size Optimization for Soil Copper(Cu) Investigation in Cropland Soil at County Scale Using Cokriging

Knowledge on spatial distribution and sampling size optimization of soil copper （Cu） could lay solid foundations for environmetal quality survey of agricultural soils at county scale. In this investigation, cokriging method was used to conduct the interpolation of Cu concentraiton in cropland soil in Shuangliu County, Sichuan Province, China. Based on the original 623 physicochmically measured soil samples, 560, 498, and 432 sub-samples were randomly selected as target variable and soil organic matter （SOM） of the whole original samples as auxiliary variable. Interpolation results using Cokriging under different sampling numbers were evaluated for their applicability in estimating the spatial distribution of soil Cu at county sacle. The results showed that the root mean square error （RMSE） produced by Cokriging decreased from 0.9 to 7.77%, correlation coefficient between the predicted values and the measured increased from 1.76 to 9.76% in comparison with the ordinary Kriging under the corresponding sample sizes. The prediction accuracy using Cokriging was still higher than original 623 data using ordinary Kriging even as sample size reduced 10%, and their interpolation maps were highly in agreement. Therefore, Cokriging was proven to be a more accurate and economic method which could provide more information and benefit for the studies on spatial distribution of soil pollutants at county scale.

County scale spatial differential characteristics of cultivated land use grade: A case of Binchuan County

Land resource is the material foundation of human survival and economic development, and the cultivated land is the essence of land resources. This paper takes the county scale, by using the method of GIS spatial analysis and statistical analysis unifies, to explore the quality of cultivated land in Binchuan County using level, and explain the utilization level of county cultivated land quality spatial differentiation characteristics. The results showed that:(1) in the quantity of cultivated land quality and utilization level, the average utilization of paddy land was greater than that of dry land, and the comprehensive utilization of cultivated land and so on. Among them, the paddy land ranged from grade 6 to 15, the average utilization was grade 11.6; dry land ranged from grade 2 to 11, the average utilization was grade 5.9; comprehensive range of cultivated land is grade 2 to 15, the average utilization was grade 8.1;(2) the quality of cultivated land utilization spatial differentiation. Paddy field, dry land and cultivated land and large value distribution in the central and southern, inverted V shape distribution; the smaller the value distribution in the East and West, a dumbbell shaped distribution. Among them, they don't use a larger value of paddy land distributed in the central, South and southwest, the maximum value is 14.3, the smaller the value distribution in the West and East, the minimum value is grade 7; the larger the value distribution by the dry land in the South and West, the maximum value is grade 10.2, the smaller the value distribution in the West and East. The minimum value is grade 2.3; the comprehensive utilization of cultivated land don't distributed larger value in the central, South and south-west, the maximum value is grade 12.7, the smaller the value distribution in the West and East, the minimum value is grade 3.5. This paper can provide scientific basis for the dynamic monitoring of cultivated land quality, the transformation of low yield farmland and the early warning of cultivated land pressure.

Simple assessment of farmland soil phosphorus loss risk at county scale with high landscape heterogeneity

In order to improve the existing phosphorus index assessment methods,using the interactive evaluation index(IEI)as an auxiliary variable,the geographically weighted regression(GWR)was adopted as prediction means.A method of regional soil phosphorus risk assessment was constructed by modifying phosphorus index model(MPIM).The GWR-IEI method more accurately predicted available phosphorus(AP)and soil organic matter(SOM),and the prediction precision and goodness of fit were high.Compared with the ordinary least square(OLS)method,the relative improvement of the root mean squared errors(RMSE)with the GWR-IEI method reached 28.95%for available phosphorus predicted,while that of SOM was 21.24%.The phosphorus loss risk of most of the study area(95.29%)was moderate to low.The areas featuring an extremely high phosphorus loss accounted for merely 0.33%of the total research area.Phosphorus loss depends on the effects of many factors.Areas which have strong source or transfer factors are not necessarily high-risk areas for phosphorus loss.Only the co-occurrence of transfer and source factors leads to high risk and greater potential for phosphorus loss.The GWR-IEI-MPIM method accurately reflected the degree of risk for phosphorus at the regional scale,which provides a valuable reference for risk assessment of phosphorus.

Statistical analysis of nitrogen use efficiency in Northeast China using multiple linear regression and Random Forest

Understanding the spatial-temporal dynamics of crop nitrogen(N)use efficiency(NUE)and the relationship with explanatory environmental variables can support land-use management and policymaking.Nevertheless,the application of statistical models for evaluating the explanatory variables of space-time variation in crop NUE is still under-researched.In this study,stepwise multiple linear regression(SMLR)and Random Forest(RF)were used to evaluate the spatial and temporal variation of NUE indicators(i.e.,partial factor productivity of N(PFPN);partial nutrient balance of N(PNBN))at county scale in Northeast China(Heilongjiang,Liaoning and Jilin provinces)from 1990 to 2015.Explanatory variables included agricultural management practices,topography,climate,economy,soil and crop types.Results revealed that the PFPN was higher in the northern parts and lower in the center of the Northeast China and PNBN increased from southern to northern parts during the 1990–2015 period.The NUE indicators decreased with time in most counties during the study period.The model efficiency coefficients of the SMLR and RF models were 0.44 and 0.84 for PFPN,and 0.67 and 0.89 for PNBN,respectively.The RF model had higher relative importance of soil and climatic covariates and lower relative importance of crop covariates compared to the SMLR model.The planting area index of vegetables and beans,soil clay content,saturated water content,enhanced vegetation index in November&December,soil bulk density,and annual minimum temperature were the main explanatory variables for both NUE indicators.This is the first study to show the quantitative relative importance of explanatory variables for NUE at a county level in Northeast China using RF and SMLR.This novel study gives reference measurements to improve crop NUE which is one of the most effective means of managing N for sustainable development,ensuring food security,alleviating environmental degradation and increasing farmer’s profitability.

Regional differentiation of ecological conservation and its zonal suitability at the county level in China

China＇s investments, financial incentives and deductions in terms of ecological conservation are based at the county level. Therefore, the monitoring and assessment of the effects of ecological conservation at the county level is important to provide a scientific basis for the assessment of the ecological and environmental quality at the county scale. This paper quantitatively estimated the dynamics of high-quality ecosystems and vegetation coverage over the past 15 years, and their relationships with the number of ecological conservation programs at the county level were analyzed. Then, the effects of ecological conservation measures on ecological changes at the county level and their regional suitability were as- sessed and discussed. The results showed that counties with a percentage of high-quality ecosystems greater than 50% were primarily distributed in northeastern China, southern subtropical China and the southeastern Qinghai-Tibet Plateau, and those with a percentage lower than 20% were mostly distributed in northwestern China, the southwestern karst region and the North China Plain. In recent decades, ecological conservation has focused on ecol- ogically fragile regions; more than five ecological conservation programs have been imple- mented in most counties of the Three River Source Region in Qinghai Province, southeastern Tibet, western Sichuan, the Qilian Mountains, southern Xinjiang and other western regions, while only one or zero have been implemented in the eastern coastal area of China. Over the past 15 years, the proportional area of high-quality ecosystems has increased in approxi- mately 53% of counties. The vegetation coverage of counties in the Loess Plateau, Huang-Huai-Hai Plain, Beijing-Tianjin-Hebei （Jing-Jin-Ji）, Sichuan-Guizhou-Chongqing, and Guangdong-Guangxi provincial-level areas has increased significantly. However, it decreased in northern Xinjiang, central Tibet, central and eastern Inner Mongolia, the Yangtze River Delta and other regions. The relationships between the numbers of ecological conservation programs and the indicators of ecosystem restoration response, such as high-quality eco- system and vegetation coverage, do not show positive correlations. These results suggest that ecological conservation programs should be planned and implemented according to the distribution patterns of high-quality ecosystems and that restoration measures such as af- forestation should follow natural principles and regional differentiation under the background of climate change.

Patterns and trends in grain self-sufficiency on the Tibetan Plateau during 1985–2016

Capacity for grain self-sufficiency on the Tibetan Plateau(TP)is an important basis for ensuring social stability and regional sustainability.Thus,based on county-level statistical data for population,grain production and consumption,we analyzed patterns and trends in grain supply and demand at regional,provincial,and county levels on the TP between 1985 and 2016.We applied two indices to evaluate capacity for grain self-sufficiency and found that the regional average self-sufficiency rate increased quickly by 1.97%/a since 1989,reaching 173.03%on the plateau over the period between 2010 and 2016.This indicates that grain supply in this region is able to fully meet demand.In addition,all provinces apart from Xinjiang exhibited similar increasing trends,attaining grain self-sufficiency during 2010–2016.Furthermore,59%of counties attained grain self-sufficiency over this period,mainly distributed in southern Tibet,in the Sichuan-Tibet junction area,and in eastern Qinghai Province.A number of gaps in grain supply and demand occurred within the headwater regions of the Yangtze and Yellow rivers as well as on the Qiangtang Plateau.Grain self-sufficiency significantly increased over the study period in 36%of counties,mainly distributed in the agricultural areas of southeastern Tibet and in eastern Qinghai.Across the whole plateau,capacity for grain self-sufficiency substantially increased between 1985 and 2016,although serious spatial imbalances remain.