MSc

The study entitled ‘Assessment of soil quality in the post-flood scenario of AEU 4 in Kottayam district of Kerala and generation of GIS map’ was conducted with the objective to assess the soil quality of post-flood soils, to work out soil quality index (SQI) and to develop GIS maps based on soil characters and quality.
Preliminary survey was conducted in four different blocks of AEU 4 in Kottayam district viz. Vaikom, Kaduthuruthy, Ettumanoor and Madapally. Seventy-five geo-referenced surface soil samples were collected from eighteen panchayats selected based on the survey. Paddy, banana, vegetables, coconut and nutmeg were found to be the major crops cultivated in the study area. Ninety-four percentage of farmers in the surveyed area were small and marginal mostly following conventional method of nutrient management.
The soil samples collected from the eighteen panchayats were analysed for various physical, chemical and biological attributes. The physical attributes included bulk density, particle density, porosity, water holding capacity, soil moisture, soil texture, depth of sand/silt/clay deposition, aggregate analysis. Soil texture for majority of the samples (68.8 percent) was sandy clay loam with water holding capacity ranging from 20.6 to 68.8 per cent. Bulk density of 50.7 per cent of samples recorded a value less than 1.2 Mg m-3 with a mean value of 1.2 Mg m-3. Particle density of 73.3 per cent samples were less than 2.2 Mg m-3. Depth of sand/silt/clay deposition was not much significant in the study area.
The chemical parameters analysed were pH, EC, organic carbon, available macronutrients and boron (micronutrient). More than 90 per cent of samples were in the acidic range with 6.67 per cent as ultra-acidic, 17.30 per cent as extremely acidic, 20 per cent as very strongly acidic, 14.70 per cent as strongly acidic, 14.6 per cent as moderately acidic and 7.61 as slightly acidic. EC value was less than 1 dS m-1 for 89.3 per cent of the samples. Organic carbon was high in 58.7 per cent samples analysed. Availability of nitrogen was found to be low in 78.7 per cent of samples, phosphorus and potassium was high in 54.7 per cent and 40 per cent samples respectively.
Among the secondary nutrients, available calcium was adequate in 88 % of samples while available magnesium was sufficient in 58.7 % samples. Sulphur availability was found to be adequate in 81.3 per cent samples and boron was deficient in 78.7 per cent samples. Activity of acid phosphatase was also analysed as a biological attribute. Activity of 41.3 percentage sample were in the range of 10 to 25 μg p-nitrophenol g-1 soil h-1
Nutrient indices were calculated from the analysed data. The analysed data was also used to set up a minimum dataset (MDS) by employing principal component analysis (PCA). Principal component analysis of 20 attributes resulted in a MDS containing seven attributes (organic carbon, available N, P, K, Ca, per cent sand and per cent silt). By giving scores and weightage to each component in the MDS, soil quality index (SQI) was worked out. The relative value for soil quality index (RSQI) was used to categorize the soil into low, medium and good quality. GIS techniques were used to prepare thematic maps of various soil parameters and soil quality indices. Simple correlations were also worked out among various analysed parameters.
Nutrient index was high for organic carbon, low for available nitrogen while it was medium for available phosphorus and potassium.
Compared to the pre flood data (KSPB,2013) soil acidity was increased as there was an increase in percentage samples in ultra-acidic, moderately acidic and strongly acidic range, an increase in organic carbon, available potassium, calcium and magnesium were observed. Even though the availability of phosphorus and sulphur were high in the AEU, percentage of samples in low fertility class was increased compared to pre-flood data. However, availability of boron was decreased and the per cent deficient soil samples considerably increased in the post-flood scenario
The study indicated that RSQI in the majority of soils of AEU 4 of Kottayam district was medium and land quality index was very low to low. The study recommends the site specific adoption of soil management strategies for the control of soil acidity, applications of soil ameliorants, micronutrients such as B for maintaining soil health and quality in the AEU 4 regions of Kerala.