Ordinary Kriging Interpolation and Smoothing Effect Correction for Soil Texture Mapping in Hetao Irrigation District
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    Abstract:

    Spatial distribution of soil texture is important for soil improvement, irrigation and drainage management, and rational utilization of water and land resources, which is usually obtained by spatial interpolation methods like ordinary Kriging (OK). However, OK generally has the smoothing effect that high values are underestimated and low values are overestimated. For soil particle-size fractions and texture interpolation, four logratio transformation methods, including additive (ALR), centered (CLR), isometric (ILR), and symmetry (SLR) logratio transformations, were firstly used to deal with soil particle-size fractions as compositional data. OK was then used to interpolate the transformed data. Finally, a model based on the back propagation neural network (BPNN) was developed to estimate the residuals between the observations and OK estimations to correct the smoothing effect. Results for the Hetao Irrigation District showed that the four logratio transformations had a discrepancy in correcting the smoothing effect. Generally, ILR had the best performance in reducing the smoothing effect. Compared with OK estimations without logratio transformations, the range smoothing rates (CR) of ILR were decreased by 5.8%, 33.8% and 45.6%, and the standard deviation smoothing rates (CS) were decreased by 38.6%, 53.9% and 60.2% for clay, silt, and sand particle-size fractions, respectively. Furthermore, the smoothing effect was obviously weakened and the interpolation errors were decreased after correction by BPNN model, where CR and CS values were reduced to 0 and 0.03~0.07, and the root mean squared errors were reduced by 19.8%, 21.0% and 14.6%, respectively. Therefore, the present correction method can not only weaken the smoothing effect caused by OK but also improve the interpolation accuracy. The spatial interpolation results obtained after the correction showed there were mainly five soil texture types in the Hetao Irrigation District, including sand, loamy sand, sandy loam, loam, and silt loam. The sandy soil mainly distributed in the western part, loam mainly in the central west, northeast, and southwest parts, and silt loam in the north part and south part close to the Yellow River. In conclusion, the OK interpolation results can better reflect the spatial distribution pattern of soil texture after the correction of smoothing effect by using the logratio transformation and BPNN model, which also provided a reference for reasonable utilization of water and land resources in Hetao Irrigation District.

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History
  • Received:March 21,2022
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  • Online: January 10,2023
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