Land evaluation and crop suitability rating of the acid sulphate soils of Kuttanad for sustainable land use planning

Abstract

An investigation was carried out at College of Agriculture, Vellayani during 2001- 2004 to delineate acid sulphate soils of Kuttanad and to develop sustainable land use plan for the area based on land evaluation and crop suitability rating with the help of GIS technology. The study consists of generation of detailed soil maps of acid sulphate soils of Kuttanad, various thematic maps of acid sulphate soils of Kuttanad, interpretation of soil maps, qualitative and quantitative evaluation of land use systems of the area, and development of a sustainable land use model taking into account the climatology, productivity and socio- economic constraints of the area. Kuttanad is a lowlying deltaic region lying 0.6 to 2.2 m below mean sea level. The reconnaissance soil survey of the area was conducted according to the principles envisaged in IARI (1970). Two profile pits were dug from each series identified and morphological features were described and surface as well as subsurface samples were drawn for detailed laboratory examination. Soil classification was done based on field survey, soil correlation and laboratory investigation and soil map of acid sulphate soils of Kuttanad was prepared based on GIS technique. Land capability classification was done based on inherent soil characteristics, degree of limitations etc. Soil site suitability classificatio~ was done to find the suitability of different crops in the region and fertility capability classification was also done for evolution of sustainable agricultural management. These soils were thoroughly evaluated to study the present land use, its suitability and to suggest alternate land use plan for the area.

The morphological and physico- chemical characteristics of the area showed great degree of variation. The soils were deep with a hue of7.5 YR to 10 YR, sticky and plastic, angular blocky to sub angular blocky in structure with textural variation from sandy to clayey with random deposits of lime shells and humus. Presence of faint to prominent reddish yellow or brown mottles in most of the soil layers. Some of the special characteristics observed were partially burned wooden logs and reddish brown root channels. The soils were extremely acidic with high organic carbon content. The CEC, ECEC and available nutrients except phosphorous were high for these soils. Due to P fixation, phosphorous deficiency is widespread. However the base saturation was below 50 per cent. As per USDA classification, the entire study area was classified under the order Entisols, with suborder Aquent, great group Sulfaquent, subgroup Typic Sulfaquent with six soil series viz., Ambalapuzha, Purakkad, Thotapally, Thuravur, Kallara and Thakazhi. As per FAO classification, these soils were included under Thionic Fluvisols. The region enjoys a humid tropical climate. Based on soil mapping of the area it is revealed that acid sulphate soils of Kuttanad cover an area of 14277.51 ha comprising of six soil series. Kallara series occupied the largest area of 6860.17 ha. The soils of the region were deep, poorly drained loamy soils in control section and are very gently sloping with slight erosion. Land capability classification of the area showed five soil senes ViZ., Ambalapuzha, Purakkad, Thuravur, Kallara and Thakazhi covenng an area of 13099.60 ha came under the class IV sw. The Thotapally series was grouped under

III sw. While considering the soil site suitability for paddy, Thotapally and Thuravur series come under subclass S2 xf ie these are moderately suitable for paddy cultivation with limitations due to fertility and pH. For coconut cultivation, all the series except Thuravur are grouped under S2 xf. Soil site suitability for mango cultivation revealed that Ambalapuzha, Purakkad and ThotapalJy senes are moderately suitable with limitations due to excess wetness, low pH and fertility limitations. As per Fertility Capability Classification, the soils belong to the units Lgac, Lgac, LCgac, Cgaics, Lgac and LCgaic respectively for Ambalapuzha, Purakkad, Thotapally, Thuravur, Kallara and Thakazhi series. The modifiers that are relevant to the acid sui phate soi I condition are "g" which defi nes wet land soi Is, "a" aluminium toxicity, "i" denotes high P fixation by iron, "c" denotes the acid sulphate soil condition. Socio - economic, cultural and ecological traits were also taken in to account along with land, crop and climatological characteristics of the area for the development of a probable land use model. Based on the study the land use models that can be suggested for the area are rotational farming involving paddy, fish and livestock.