EVALUATION OF SOIL-WATER RETENTION MODELS BASED ON BASIC SOIL PHYSICAL-PROPERTIES

Algorithms to model soil Hater retention are needed to study the response of vegetation and hydrologic systems to climate change. The objective of this study was to evaluate some soil water retention models to identify minimum input data requirements. Six models that function with various combinations of particle-size distribution, bulk density (rho(b)), and soil organic matter data Here tested using data for nearly 6000 pedons. The Rawls model, which requires particle-size distribution and organic matter data, had the low est overall absolute value of the mean error (ME) with 0.020, 0.001, and 0.007 m(3) H2O m(-3) soil for matric soil water pressures of -10, -33, and -1500 kPa, respectively. The Saxton model, which requires particle-size distribution data, had small MEs (0.018 and 0.007 m(3) H2O m(-3) soil) for -10 and -1500 kPa matric soil water pressures, and a moderately small ME (0.017 m(3) H2O m(-3) soil) at -33 kPa. The Vereecken model, which requires rho(b), particle-size distribution, and organic matter data, had small MEs (0.016 and 0.009 m(3) H2O m(-3) soil) at matric soil water pressures of -10 and -33 kPa, with a larger ME (0.020 m(3) H2O m(-3) soil) at -1500 kPa. The remaining three models had relatively large MEs for at least two of the three matric soil water pressures. For estimating water-holding capacity only, the Saxton model is adequate. The Rawls model is recommended for characterizing the relationship of water content to matric soil water pressure.