|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
Alisols - Soils of NW-Thailand
In NW-Thailand, Alisols prevail on moderate to steep sloping land on siliceous sedimentary rocks until 1000 m asl. Above 1000 m asl these soils occur in association with Acrisols.
Sandstone and mudstone landscape dominated with Alisols under maize (top left) and upland rice cultivation (top right). Profiles of Alisols on sandstone (bottom left) and mudstone (bottom right).
On mudstone, most topsoils have a clay loamy texture with a crumbly structure. The transition to the underlaying Argic horizon (clay enriched subsoil) is mostly clear and smooth, lacking an E-horizon in between. The Argic horizon has a clayey texture and shows a subangular blocky structure. These soils are mainly used for the production of upland rice, maize, soybeans, and red kidney beans.
On fine-grained sandstone, Alisols 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.
Alisols from coarse-grained sandstone, breccia, and conglomerates show an A-horizon with a texture of sandy loam to sandy clay loam generally in subangular blocky structure. The E-horizon (clay depleted subsoil) consists of sandy clay loam to loam either subangular blocky structured or containing single grains. The Argic-horizon below is dominated by clay loam and clay with a subangular blocky structure. While the topsoil is dominated by the sand fraction, the clay fraction is clearly prevailing for the subsoil. The total soil thickness ranges between 1 and 2m. These soils feature mostly abrupt clear horizon boundaries.
On limestone, Alisols dominate on moderate to steep sloping land at lower elevations, at 800 m asl these soils pass over to Acrisols. Most Alisols 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 Alisols. These soils are mainly used for maize production. At sites with many limestone outcrops these soils are associated with Leptosol and covered with forests.
Alisols are commonly used for upland rice and maize production. Generally, the main nutrient stock 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