The Soils of Sri Lanka by Unknown

Author:Unknown
Language: eng
Format: epub
ISBN: 9783030441449
Publisher: Springer International Publishing

5.2.3.3 Soils Representing the Minor Flood Plains of the Dry Zone

The Omadiamadu Series which occurs in the levee and valley bottoms of the minor flood plains is selected as the benchmark soil to represent this landscape. This is named as Old Alluvial soils in the local classification and according to WRB legend classified as Gleyic Fluvisols (Eutric). According to Soil Taxonomy it is classified as Sodic Psammaquents.

Old Alluvial Soils—Omadiyamadu Soil Series

Soils of Omadiyamadu series are formed resulting from alluvial/colluvial deposition along the minor streams occur in the valley bottom physiographic positions within undulating topography east of Polonnaruwa (Mahaweli System B Feasibility Report 1978). These depositions are narrow and prone to flash floods during the rainy season. Generally, these streams are dry and become active only in the rainy season from late October to early February. At present most of the lands belonging to this soil series are under irrigated rice cultivation and therefore, surface soil features and drainage characteristics are quite different from similar soil occurring under natural forest vegetation. In most locations, decomposing parent material similar to the soils derived from Non-Calcic Brown Great Soil Group could be seen about 1–1.5 m depth from the surface because recent alluvial/colluvial depositions are on the old land surface with soils derived from in situ parent material. These soils are poorly drained mainly due to the influence of groundwater table fluctuations. Depth of soil is generally moderately deep but deep soils could also be seen in some second- and third-order valleys. Color of the soil varies from brown, dark grayish brown to greenish gray with depth (Fig. 5.16). In locations where groundwater influence is prominent, subsurface soil is completely gleyed and greenish in color. Black color ferromanganese concretions could be seen within the subsurface Texture of the surface soil is sandy loam compared to the sandy clay loam subsurface soil. Soil structure development of this soil is poor. However, structure of the surface soil is weakly developed subangular blocky under cultivated environment. Subsurface soil is structureless or massive. Consistency of the surface soil is nonsticky and plastic when wet, friable when moist, and hard when dry.

Fig. 5.16Landscape and soil profile of Omadiyamadu Series (Soil Taxonomy: Sodic Psammaquents; FAO/WRB Legend: Haplic Arenosols, Calcaric, Eutric)

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