Assessment of Soil Quality Index in the Southern Coastal Sandy Soils of Kerala, India

Context: The Indian state of Kerala has a long coastline of 589.50 km all along its western border, which has a great potential in biomass production. The agro-ecological unit 1 (AEU 1) in Kerala represents the southern coastal plains, with typical sandy soils. The major constraints of these coastal sandy soil with regard to agriculture are: low organic matter and clay content, as well as their poor water holding capacity, resulting in limited ability to hold nutrients.

Aims: A study was carried out to evaluate the physico-chemical parameters and quality of the soils of coastal sandy soils in AEU 1.

Methods: Fifty geo-referenced composite soil samples were taken from different locations of AEU-1 in Thiruvananthapuram district, and were characterised for physical, chemical and biological attributes. Principal component analysis (PCA) was carried out for the analysed soil properties which resulted in 6 principal components (PCs) and a minimum data set (MDS) was obtained using the selected indicators i.e., texture (clay %), water holding capacity, bulk density, soil pH, organic carbon, available nutrients such as potassium, sulphur, zinc, manganese and boron. The soil indicators were changed to unit-less scores after the development of MDS, and were assigned with appropriate weights based on existing soil conditions and soil nutrient content.

Key Results: Value of SQI recorted the highest in Kadakkavoor and the lowest in Anchuthengu. Further, the locations were classified into three groups namely poor, medium, and good, based on the relative soil quality index (RSQI). Less than 50% of RSQI is considered poor, from 50% to 70% is medium, while more than 70% is considered good. From the study, majority of the land area (60% of samples) in AEU 1 of Thiruvananthapuram district were observed to have a medium level of relative soil quality index.