Modern land surface model simulations capture soil profile water movement through the use of soil hydraulics sub-models, but good hydraulic parameterisations are often lacking, especially in the tropics. We present much-improved gridded data sets of hydraulic parameters for surface soil for the critical area of tropical South America, describing soil profile water movement across the region to 30 cm depth. Optimal hydraulic parameter values are given for the Brooks and Corey, Campbell, van Genuchten–Mualem and van Genuchten–Burdine soil hydraulic models, which are widely used hydraulic sub-models in land surface models. This has been possible through interpolating soil measurements from several sources through the SOTERLAC soil and terrain data base and using the most recent pedotransfer functions (PTFs) derived for South American soils. All soil parameter data layers are provided at 15 arcsec resolution and available for download, this being 20x higher resolution than the best comparable parameter maps available to date. Specific examples are given of the use of PTFs and the importance highlighted of using PTFs that have been locally parameterised and that are not just based on soil texture. We discuss current developments in soil hydraulic modelling and how high-resolution parameter maps such as these can improve the simulation of vegetation development and productivity in land surface models.

The variation in live and dead fine root weights with soil water regime was studied on three sites supporting closed-canopy stands of Sitka spruce (Piceasitchensis (Bong.) Carr.). Soil types were a very poorly drained peaty gley, an imperfectly drained peaty gley, and a freely drained podzolized brown earth. Fine root material was extracted from replicate cores (0–10 cm) and categorized as live or dead. Live fine root weight, live to dead fine root ratio, and the number of live fine root tips all differed significantly between sites, decreasing with increasing dryness of the soil water regime.