Assessment and GIS Mapping of Soil Quality Indicators of Agroecological Unit 9 of Kerala, India

Context: The agroecological unit 9 (AEU 9) in Alappuzha district of Kerala represents the south central laterites. The soils are acidic, gravelly, having low activity clay, often underlain by plinthite with low water and nutrient retention capacity. Assessment of soil quality indicators and mapping of resources and soil fertility status is essential for planning and development activities.

Aims: Soil quality assessment was made by collecting observations on physical, chemical and biological indicators, soil quality index was computed and generated maps using GIS.

Study Design: Survey, collection of soil samples and principal component analysis.

Place and Duration of Study: A study was conducted in agroecological unit 9 (south central laterites) in Alappuzha district of Kerala during 2020.

Methods: Geo-referenced composite soil samples were collected from 75 locations of AEU9 in Alappuzha district, and were characterized for physical, chemical and biological attributes for evaluating soil quality. Principal component analysis (PCA) was carried out for soil parameters and a minimum data set (MDS) was arrived from seven principal components (PC 1 to PC 7) with eigen values greater than 1. The selected soil quality indicators were categorized into classes, assigned with scores and soil quality index was computed. Based on soil quality index, soils were rated as poor, medium or good. GIS based thematic maps of soil quality indicators and index were prepared.

Results: The soils of AEU 9 are sandy loam in texture, strongly acidic (pH 4.5-5.5), medium in organic carbon, low in available N, medium in available P and K, deficient in available Ca, Mg and B. Majority (80%) of the soils are rated poor and 20% rated medium in soil quality. From the study it is concluded that pH, clay%, bulk density, available nutrients N, P, K, Ca and S are the key indicators of soil quality in AEU 9.