Water Retention Capacity in Coarse Podzol Profiles Predicted from Measured Soil Properties

Fennoscandian podzols consist of coarse parent materials with a strongly developed secondary structure in the Spodic B-horizons. For such materials, predictive standard water retention models developed for soils with a wide range of texture, including fine clay-rich soils, do not give estimates of water retention capacity with high enough precision. In this study we describe an approach to predict water content of coarse podzolic soils separately at seven potentials using multiple linear regression approach and stepwise regression analysis (Rawls et al., 1982, 1983). One model is constructed using only the easily measurable soil texture and dry bulk density data. To include the effects of secondary structure, two other models are constructed by using several measured soil physical and chemical properties for all horizons, or for all horizons excluding the eluvial horizons. These models explain between 90 and 95% of variation in water content (i.e., R2 = 0.90–0.95) at potentials −3.2 to −100 kPa and at saturation, but not at the −1585 kPa potential. The validity of the models is tested on soils from four different sites covering a large range of soil properties of Fennoscandian podzols. Two of the models give accurate estimates of water content with errors ≤0.02 ± 0.03 m3 m−3 at potentials of −10 kPa, −100 kPa, and at saturation. Results show that podzolization processes, including formation of secondary structure by enriched Al and Fe, affect soil water retention, but estimates based on oxalate extractable Al and Fe content cannot be generalized to other soils using the same model calibration.