Development of Agricultural Soil-Profile Physical Properties Database, Japan: SolphyJ.

Regional or watershed scale assessment of water flow and chemical transport in soils by mechanistic models generally requires soil-profile physical properties dataset categorized by soil as well as land-use types. We developed the Agricultural Soil-Profile Physical Properties Database, Japan (SolphyJ) based on a whole nation-scale agricultural soil survey project that was performed at about 19,000 survey points with an interval of 5 yr during the 20-yr period of 1979 to 1998 by the 47 prefectural agricultural research institutes, financially supported in part by the Ministry of Agriculture, Forestry, and Fishery.

The database consists of the descriptive statistics such as mean, median, standard deviation, 1^st and 3^rd quantiles, minimum and maximum, coefficient of variance, 95% confident interval, skewness, kurtosis, etc., for each population of the basic 17 soil physical properties (thickness; bulk density; particle density; hardness; clay, silt, fine sand, coarse sand, and total sand contents; porosity; volumetric water content at sampling and those at suction heads of 32, 5.0 × 10², 1.6 × 10⁴, and 3.2 × 10⁵ cm; saturated hydraulic conductivity; and total carbon content) grouped by the 1^st to up to 6^th soil horizons, 60 Soil Series Groups (Japan Agricultural Soil Classification System, 1983), and 5 agricultural land-use types (paddy, upland, orchard, grassland, and green-house fields). The database also includes the figure of frequency distribution and fitted normal curve, and the results of normality and lognormality tests, for each population. These contents will be able to be freely downloaded as Microsoft Excel and Adobe Acrobat PDF files from the internet homepage of the National institute for Agro-Environmental Sciences.

The SolphyJ first provides the topsoil-to-subsoil average physical properties dataset categorized by soil as well as land-use types at a whole nation scale. The users can readily construct the average soil physical properties profile to a depth of about 1 m only from the geographical information of soil and land-use types and simulate the water flow and chemical transport in soils by appropriate mechanistic models after determination of the soil water characteristic curves and relevant model parameters from the database.