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Soil properties and land use affecting soil water dynamics in Andisols and Inceptisols at two mid-elevation sites in the Colombian Andes

University of British Columbia

Soil has a crucial role in the terrestrial component of the hydrologic cycle, regulating the availability of water for ecosystem services. Yet relationships between soil properties and land use for the major soil types in the Colombian Andes have not been extensively studied. This study evaluated soil water (SW) dynamics of two soils types, belonging to the most common soil orders in the Colombian Andes, Andisols and Inceptisols. The research was conducted in two watersheds at mid-elevation, and focused on the relationships between mineralogical, physical and chemical soil properties with soil water dynamics, including soil water retention (SWR) and field saturated hydraulic conductivity (Kfs). The Andisols and Inceptisols of this study have a large total porosity compared to typical clay soils, but Andisols, showed higher SWR at every soil tension relative to Inceptisols. Notwithstanding the high hygroscopic water (θPWP), both soils have a wide pore size distribution, with similar gravitational water and plant available water storage capacities. Despite differences in climate and soil parent material between watersheds, the presence of colloids with high specific surface area in both soils (allophane, imogolite, ferrihydrite and organo-metallic complexes in Andisols and ferrihydrite and Al/Fe oxides in Inceptisols) contribute to high SWR. Within each site, differences in SWR between land uses appear minimal, although soil organic carbon was lower under pasture in both soils. The limited differences in SWR between natural forest and pasture appear to reflect the effects of short-range order (SRO) minerals and organo-metallic compounds on SWR, which offset differences in SOC between natural forest and pasture. Quasi steady-state infiltration rates measured in the field did not correspond to expected values based on texture alone, highlighting the importance of field based measurements, particularly in soils with SRO minerals. Additionally, there was a pronounced seasonal difference in Kfs under pasture in both soil types, and a negative correlation of soil water content with Kfs in Inceptisols. Determination of physical, chemical and mineralogical properties was found to be crucial in understanding soil water dynamics in this study, and future work should include an assessment of SRO minerals in addition to SWR characteristics.

Text

2018-08-25

Attribution-NonCommercial-NoDerivatives 4.0 International

http://hdl.handle.net/2429/66968

Soil Science

University of British Columbia

UBCV

http://creativecommons.org/licenses/by-nc-nd/4.0/