MSc

ABSTRACT
The present study was carried out during 2018-20 in the Department of Soil Science and Agricultural Chemistry, College of Agriculture, Vellayani. The study was envisaged to assess the soil quality of post flood soils of AEU 4 in Alappuzha district and to work out soil quality index (SQI). A preliminary survey was conducted using a pre-designed questionnaire to assess the effect of flood and cropping history of the locality. Rice is the major crop cultivated in the study area and majority of the farmers follow conventional method of farming practices in the paddy fields. On the basis of survey conducted in the post flood areas, 75 geo referenced surface soil samples were collected from 17 flood affected panchayats of AEU 4 in Alappuzha district. The soil samples were analysed for physical (bulk density, particle density, porosity, moisture content, water holding capacity, aggregate stability), chemical (pH, EC, organic carbon, available N, P, K, Ca, Mg, S and B) and biological (acid phosphatase) attributes.
From the study, it was observed that bulk density of 78.67 per cent of samples were lower than 1.20 Mg m-³ while that of particle density of 81.34 per cent of samples were less than 2.2 Mg m-³. The lowest value for particle density was observed in Kavalam (1.67 Mg m-³). Neelamperoor recorded the highest value for porosity (64.7 per cent), clay content (42.3 per cent) and water holding capacity (57.1 per cent) and the lowest value for sand per centage (22.7 per cent) and bulk density (0.66 Mg m-3). The predominant textural class observed in the soil samples of the study area belonged to sandy clay loam category.
From the perusal of the data, it was observed that 78.67 per cent soils were extremely acidic and 98.67 per cent of samples had EC less than 1 dS m-1. 94.67 per cent of soils were high in organic carbon content and the highest value was recorded from Neelamperoor (5.39 per cent). With regard to major nutrients, available nitrogen content was medium (69.34 per cent), available phosphorus content was low (48 per cent) and Available potassium was high (76 per cent) for most of the samples. Highest and lowest values for available Ca and Mg were recorded from Kainakary and Pandanad respectively. In the case of boron, 93.33 per cent of samples were deficient in boron. Acid phosphatase activity was found to be the highest in Veliyanad and while the lowest value was noticed in Ambalappuzha South panchayat.
Soil quality evaluation was done by scoring of indicators in minimum data set and integration of the indicator scores into SQI. Statistical tool, principal component analysis (PCA) was used for the selection of MDS and the indicators selected include porosity, WSA, sand content, pH, EC, organic carbon, available K, Ca, Mg and B and acid phosphatase. The highest SQI was reported in Veliyanad while the lowest value was recorded from Puliyur.
Land Quality Index (LQI) and Nutrient index (NI) were computed for the study area and LQI was the highest for Purakkad (8.39) followed by Veliyanad (6.47). Kavalam reported highest value for nutrient index of nitrogen whereas Kainakary reported the highest nutrient index value for phosphorus. Correlation study of the analysed parameters was carried out and thematic soil maps were generated for the analysed parameters using ArcGIS software.
Comparative evaluation of pre flood data from State Planning Board (2013) with that of the post flood data generated in the present study revealed that soil acidity has increased after flood. The flood has a positive impact on organic carbon content, available K, Ca and Mg by increasing the status while the status of available P and B got decreased.