Spatial interpolation of soil moisture retention curves

Abstract Methods for interpolating soil moisture curves at unrecorded sites from measurements of soil water content at fixed pressure heads at sample points are investigated. A spatial prediction procedure was devised with two steps: interpolation of the retention data followed by fitting the Van Genuchten function to the interpolated values. For the interpolation, four different methods were considered. Two are based on a tessellation into areas of equal values, namely the nearest neighbour and the soil classification. The other two were autokriging and cokriging. The performance of these methods were compared in an area of 92 ha of alluvial soil where soil changes were gradual. Mean deviations and mean square deviations between predicted and observed retention data at validation sites were compared for two sampling densities. Kriging performed best in both cases. Cokriging was only slightly better than autokriging, and the latter is recommended for use. The performance of the nearest neighbour method diminished markedly with decreasing sampling density. Conversely, the performance of soil classification diminished only slightly, and this technique appeared as a reasonable alternative to kriging for sparse samples.

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