Estimating soil water retention characteristics from the soil taxonomic classification and mapping informations: Consideration of humus categories

Abstract

The main limiting factors of soil fertility in Hungary are related to soil water management. For this purpose the water management category systems was elaborated in the scale of 1:100 000 and 1:10 000 (Varallyay et al., 1980, Varallyay, 1989). Soil water-retention characteristics (SWRC) are important factors of that category system, but they can only be measured at limited number of sites in a routine soil survey. From this reason most of the soil survey organizations have established soil information systems for further investigations. Data collected in fields and laboratories, for example soil horizons, texture, structure, organic matter, and carbonate content, etc. are prepared for mapping and for further evaluation, and utilization. Even systematic sampling to obtain spatially distributed hydrophysical input data for simulation models is also practically impossible because direct measurement of soils' hydraulic properties is expensive, time consuming, and labor intensive. Alternatively these properties are predictable from available soil data as bulk density (BD), organic matter (OM) content and particle-size distribution (e.g. Gupta and Larson, 1979; Rawls et al., 1982; Ahuja et al., 1985; Fodor and Rajkai, 2004; Rajkai et al., 2004). Estimating functions of the required parameters from easily obtainable input data are called pedotransfer functions (PTFs) according to Bouma and Van Lanen (1987). Soil maps are visualizing the data collected by the standard soil survey methods. Soil surveys are usually built on soil taxonomic classification and additional data, depending on the special requirement of the survey. Soil maps display not only the soil type, but also other soil attributes with certain categorization. Land evaluation is one of the most widespread applications of soil data for land use planning purposes. For land evaluation purposes maps of a scale of 1:10.000 are required. About 60 % of the agricultural area of Hungary is mapped in this scale (Toth et al., 2004). Many of the maps are digitized, georeferenced and integrated to GIS systems. The 1:10.000 maps in Hungary contain information on soil types (subtypes), parent material and texture. Five additional cartograms complement the basic soil map: (1) humus cartogram (with information on depth of humic layer and humus content of the plough layer); (2) pH and calcium carbonate content cartogram; (3) ground water cartogram (depth of soil water level); (4) cartogram of soil salinity (with information on salt content and distribution in the soil profile) (5) cartogram of soil characteristics those are important in soil fertility and management (rooting depth, erosion, stone content, etc.). The 1:10.000 scale map database is the most extensive and it represents the most soil types in Hungary. Therefore it would be very advantageous to find estimation methods for converting the raw data of soil maps and cartograms as readily available information for determining the soil water management categories. This paper aims to formulate the SWRC dependency of the Hungarian soil taxonomic classification in the case of brown forest soils.