|Research Sites in Northern Thailand: Bor Krai, Huai Bong, Mae Sa Mai|
Soils of NW-Thailand: (a) Major Soils: Acrisols, Alisols, Cambisols; (b) Minor Soils: Anthrosols, Ferralsols, Fluvisols, Gleysols, Leptsols, Luvisols, Plinthosols, Regosols, Technosols, Umbrisols; (c) Exotic Soils: Chernozems, Histosols, Stagnosols, Vertisols
Acrisols - Soils of NW-Thailand
In NW-Thailand, Acrisols prevail on moderate to steep sloping land on granite and gneiss until highest elevations. Thereby, the degree and depth of clay illuviation is decreasing with increasing elevation, indicating that clay is mainly mechanically translocated via cracks, which were formed after the soil dried out.
Granite and gneiss landscape dominated with Acrisols under lychee and vegetable cultivation (top). Profiles of Acrisols on granite (bottom).
At highest elevations Acrisols pass over to Ferralic Cambisols. Most Acrisols on granite and gneiss show reddish soil colours. Often mica is preserved throughout the whole soil profile. Most topsoils have a clay loamy texture with a crumbly structure. The transition to subsoil is mostly clear and smooth. The subsoil has a clayey texture and shows a subangular blocky structure. These soils are mainly used for the production of lychee, maize, upland rice and vegetables.
On limestone, Acrisols dominate on moderate to steep sloping land above 800 m asl until highest elevations. Most Acrisols feature topsoil with a clay loam or clay texture showing a strong crumbly structure. The transition to the Argic horizon (clay enriched subsoil) is mostly clear and a prominent E-horizon is missing. The Argic horizon commonly consists of clay loam and clay with a strong subangular blocky structure. Most of them can be classified as Profondi-Humic Acrisols. These soils are mainly used for maize production. In former times Acrisols were also used for poppy cultivation. At sites with many limestone outcrops these soils are associated with Leptosol and covered with forests.
On siliceous sedimentary rocks, Acrisols occur above 1000 m asl on moderate to steep sloping land in association with Alisols. Most Acrisols have a sandy clay loam texture and a weak subangular blocky structure throughout the whole profile. The diagnostic Argic horizon has only slightly higher clay contents than the topsoil, and is mainly characterised by the presence of clay skins. These soils are commonly used for upland rice and maize production. Generally, the main nutrient stock of Acrisols is restricted to the topsoil. This "fertile" topsoil is often reduced in thickness or already totally eroded due to widespread unsustainable land use practices.
|copyright Ulrich Schuler 2008-2010|