Estimating soil hydraulic properties of Fengqiu County soils in the North China Plain using pedo-transfer functions

The unsaturated soil hydraulic characteristics, including soil water retention curve and hydraulic conductivity, are the crucial input data for simulating soil water and solute transport through the unsaturated zone at regional scales using GIS, and are expensive to measure. These properties are frequently predicted with pedo-transfer functions (PTFs) using the routinely measured soil properties (e.g. soil texture, soil bulk density, and soil organic matter content). In this study, 63 soil water retention curves and 36 saturated soil hydraulic conductivities of seven soil profiles collected in Fengqiu County in the North China Plain were measured. Soil texture, bulk density and soil organic matter of these soil samples were also measured. The van Genuchten model describing soil water retention was used to fit the measured data for quantifying the soil hydraulic parameters. The PTFs were developed by multiple regression between soil hydraulic parameter data and basic soil properties. The double cross-validation of these PTFs is also discussed in this paper. The locally-developed PTFs from this study were compared with several existing PTFs in predicting the soil hydraulic parameters. The developed PTFs were used in the regional simulation of a wheat and maize cropping agroecosystem in Fengqiu County for the 1998–1999 rotation year, and can explain 33% of spatial variation of the observed crop yields in 409 villages.