Assessment of soil quality in the post - flood scenario of AEU 9 in Pathanamthitta district of Kerala and generation of GIS maps

Abstract

A study entitled “Assessment of soil quality in the post-flood scenario of AEU 9 in Pathanamthitta district of Kerala and generation of GIS maps” was carried out during 2018-20 with the objective to evaluate the soil quality in the flood affected areas of AEU 9 of Pathanamthitta district, to work out the soil quality index and to generate maps of various soil attributes and quality indices using GIS techniques. Survey conducted to identify the flood affected areas in AEU 9 of Pathanamthitta district revealed that the flood affected panchayats includes Kaviyur, Thumbamon, Kulanada, Thottapuzhassery, Kallupara, Mezhuvely, Panthalam, Kozhanchery, Aranmula, and Mallapally. All these panchayats were severely affected by flood havoc and submergence that occurred in Manimala, Pamba and Achankovil rivers during August 2018. A total of seventy five geo referenced surface soil samples were collected from the flood affected panchayats and analyzed for various physical, chemical and biological attributes. Minimum data set of soil indicators for computing soil quality was selected using principal component analysis. The selected parameters were sand content, bulk density, available B, available S, available K, available Mn and organic carbon. Scores and weights were assigned to each selected indicator, and computed the soil quality index. GIS techniques were used to generate thematic maps of various soil attributes and soil quality indices. Sediment deposition was observed in all panchayats, while highest deposition of sand and silt were observed in Aranmula and Thumbamon panchayats. The flood did not cause much alteration in the soil texture of AEU 9 of pathanamthitta. The dominant textural class was loam. The particle density and bulk density of soil ranged from 2.07 to 2.45 and 0.87 to 1.76 Mg m -3 respectively. More than 89 per cent of the soils showed porosity in the range of 50 to 80 per cent. The soil moisture content ranged between 15.2 to 50.8 per cent. The water holding capacity and water stable aggregates ranged from 25.4 to 62.4 per cent and 38.6 to 68.5 per cent respectively. 137The electrical conductivity of soil ranged between 0.05 and 0.40 dS m -1 . Post flood soil showed an increase in the organic carbon status of the soil. Majority (95 %) of soil comes under medium and high organic carbon status after flood. About 54.7 per cent of the soils are medium in available N content. Available phosphorus content varied between 8.10 and 104 kg ha -1 with a mean of 31.9 kg ha -1 and available potassium varied between 78.7 and 493 kg ha -1 with a mean of 246 kgha -1 . The post flood soils are adequate in available sulphur (92 %) and deficient in boron status (100 %). The soil quality analysis revealed that majority of soils had high soil quality index (86.7%). Land quality index was very low in 64 % of soils while 32 % samples showed low land quality index. Nutrient index for nitrogen was low in most of the panchayats, medium and high for phosphorus, potassium and organic carbon. The results of the study revealed that most of the soil became strongly acidic after flood. Organic carbon, potassium, phosphorus and sulphur are high and medium status while nitrogen is low in most of the panchayats. Deficiency of calcium and magnesium increases after flood. The entire study area showed deficiency of boron. The results outline the need for regular liming to control soil acidity and alleviate calcium deficiency. It is also suggested to supplement magnesium and boron to improve soil quality.