2024 Volume 23 Issue 4 Pages 101-120
To clarify the water retention characteristics of forest soils in the Kyushu-Okinawa region, we applied the van Genuchten model to 513 pore distribution analyses from the appendix of Hotta's 1997 Ph. D thesis, extracting four water retention property values (m, ψ0, gravitational water content, readily available water content). We then compared these values among eight soil types. The results indicated that the Reddish/Yellowish Brown and Red and Yellow soil types exhibited low gravitational and readily available water contents, while the Black soil type showed high readily available water content but low gravitational water content and a dispersed pore size distribution. The Immature soil type consisting of coastal dune sand, had a smaller peak pore size and a more concentrated pore size distribution. Comparing the Dry and Moist Brown forest soil types revealed that the latter had a higher readily available water content and a more dispersed pore size distribution. To enhance the accuracy of models predicting the effects of climate change on catchment runoff, tree growth using forest soil water retention data, ongoing collection and development of such data across various regions, parent materials, and soil types are essential.
