Assessment of soil quality in the post flood scenario of AEU 3 in Alappuzha district of Kerala and generations of GIS maps

Abstract

A study entitled “Assessment of soil quality in the post-flood scenario of AEU 3 in Alappuzha district of Kerala and generation of GIS maps” was carried out with objectives to evaluate the soil quality of the flood affected areas of AEU 3, to work out the soil quality index and to map the various soil attributes and quality using the GIS techniques. A survey was conducted to identify the flood affected areas in the AEU 3 and identified Chunakkara, Veeyapuram, Palamel, Chettikulangara, Nooranadu, Pathiyoor and Chennithala panchayths as the major flood affected areas. The major land uses in the AEU 3 were rice, coconut, banana and vegetables. Majority of the farmers were marginal (91.5 per cent) and a few were small farmers. 28.6 per cent of farmers followed organic practices and the rest followed inorganic/ INM practices. Seventy geo-referenced surface soil samples were collected from seven flood affected panchayaths and characterized for various physical (texture, bulk density, particle density, porosity, aggregate analysis, soil moisture, WHC and the depth of silt/sand/clay deposition), chemical (pH, EC, organic carbon, available macro and micronutrients and heavy metal contents (Pb, Ni, Cd, Cr) and biological attributes (acid phosphatase and dehydrogenase activity). Principal component analysis was used to set up the minimum data set of the indicators to compute the soil quality index. Seven principal components were extracted from which nine indicators that highly influenced the soil quality were identified, viz. sand per cent, available P, available Ca, available Mg, bulk density, per cent of water stable aggregates, organic carbon, available Zn and available B. Scores and weights were assigned to each indicator, and they were aggregated to compute the soil quality index. The relative soil quality index of the soils were also found. GIS techniques were used to prepare thematic maps of various soil attributes and relative soil quality indices of the flood affected areas of the AEU 3. Correlations were worked out among the various analysed parameters. The acidity of the flood affected areas increased in comparison with the pre flood scenario. Depletion of nutrients like nitrogen, potassium, magnesium, sulphur, copper, and boron were also noticed in the post-flood soils. Available P content of the soil came down slightly from the very high status, but still continues to be high. Mg, S, Cu and B were deficient in 100 per cent of the samples, whereas, Fe and Mn remained sufficient. Ca and Zn exhibited 27.1 and 14.3 per cent deficiency, respectively. Heavy metals like Pb, Ni and Cr were detected (below critical limit) in the analysed samples, with relatively higher content in Veeyapuram. Physical properties like MWD, per cent WSA, soil moisture and WHC and biological attributes were positively correlated with the organic carbon content. Nutrient indices of nitrogen and potassium were low in most of the areas where as nutrient index of phosphorus was high throughout the AEU. 91.4 per cent samples fell into very low land quality and 8.6 per cent into the low land quality. Majority of the soils belonged to medium soil quality (78.6 per cent), followed by poor (12.8 per cent) and good (8.6 per cent) quality. The soils of Nooranad panchayath recorded the highest soil quality index and that of Chettikulangara panchayath, recorded the lowest. The increase in the acidity of the post flood soils, demands the application of adequate liming materials. Addition of more organic inputs can minimise the physical constraints of Onattukara soils. Split application of N and K fertilizers can reduce the leaching losses. Dose of P fertilizer has to be modified in the light of high P status in the AEU. Monitoring of secondary and micronutrients on regular basis is also required. Site specific and crop specific nutrient management is required to restore the soil health in the post-flood soils of AEU 3.