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Preprocessing for soil data is necessary for both SWAT modeling and soil hydraulic characteristic estimation. The soil map and soil properties dataset derived from the CSSD are based on a soil genetic classification system. From high to low level, soil group, soil subgroup and soil species are three soil categories involved. The physical properties data are at soil species level, whereas the soil map only contains soil spatial distribution at the soil subgroup level. The properties of each map unit (at soil subgroup level) are extracted from the dataset by finding the record (at soil species level) in the dataset at which the location description best matches the spatial distribution of the map unit. Each record usually contains observations from more than one soil profile. Arithmetic means of each type of observation in these soil profiles are used as properties for the corresponding map unit. To keep the number of soil parameters in SWAT model at a manageable level, all map units belonging to the same soil group are merged. In other words, map units are aggregated into the soil group level. Then, soil properties of the soil subgroup of largest area in a soil group are treated as the properties of the soil group. The soil particle distribution is converted from the international classification system used in CSSD into the US Department of Agriculture (USDA) classification system, as required by SWAT model. The spatial distribution and properties of the three soil types in Jinjiang Basin are shown in Figure 2 and Table 1.
Table 1

Properties of three main soil types in Jinjiang Basin

Soil group namePercentage of area (%)Clay (%)Silt (%)Sand (%)Organic matter (%)
Red soil 67 45.7 23.8 30.5 6.05 
Paddy soil 28 10.6 17.0 72.4 2.78 
Yellow soil 27.8 24.1 48.1 12.8 
Soil group namePercentage of area (%)Clay (%)Silt (%)Sand (%)Organic matter (%)
Red soil 67 45.7 23.8 30.5 6.05 
Paddy soil 28 10.6 17.0 72.4 2.78 
Yellow soil 27.8 24.1 48.1 12.8 
Figure 2

Spatial distributions of three soil group types.

Figure 2

Spatial distributions of three soil group types.

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