MSc

ABSTRACT
A study entitled “Assessment of soil quality in the post-flood scenario of AEU 9 of Alappuzha district in 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 Alappuzha district, to work out the soil quality index and to generate maps of various soil attributes and quality using GIS techniques.
Survey conducted to identify the flood affected areas in AEU 9 of Alappuzha district revealed that the entire area of AEU 9 in Alappuzha district was affected by flood. Chengannur municipality was the worst affected followed by Mulakkuzha, Ala, Cheriyanad and Venmony panchayaths. About 75% of the study area was under coconut based cropping system with marginal farmers (72.1%) practicing integrated nutrient management (70.6%).
Geo referenced surface soil samples (0-20 cm) were collected from seventy five sites from the five flood affected panchayaths and characterized for various physical, chemical and biological attributes. Minimum data set of soil indicators for computing soil quality were selected using principal component analysis. The selected parameters were clay per cent, bulk density, electrical conductivity, available N, available P, available K, available Ca, and available S. Scores and weights were assigned to each selected indicator, and were aggregated and soil quality index was computed. GIS techniques were used to generate thematic maps of various soil attributes and soil quality indices.
The dominant textural class was sandy loam. The particle density and bulk density of soil ranged from 2.10 to 2.60 and 1.10 to 1.80 Mgm-3respectively. Majority (66.7%) of the soils had porosity in the range of 50 to 70%. The soil moisture content ranged between 11.33 to 24.44%. The water holding capacity and water stable aggregates ranged from 32.12 to 74.63% and 37.3 to 70.6% respectively. Deposition of sediments was observed in all the panchayaths with maximum deposition of 10 to 15cm thickness in Chengannur, Cheriyanad and Vemony. There was an increase in soil acidity after floods and 20% of the soils became extremely acidic (3.5-4.5). The electrical conductivity of soil ranged between 0.10 to 0.60 dSm-1. An increase in organic carbon status was observed post flood with 38.7 % of soils having high organic carbon content compared to 18 % before the floods. The available nitrogen in soil ranged between 100 and 627 kg ha-1 with 89.3 % of soils in low category. A decrease in available phosphorous, calcium and magnesium was observed in the post flood soils. Available P was low in 13.3 % of soils and 64 % of soils were deficient in calcium while all the soils were deficient in magnesium and boron. Available K was medium to high (100 to 492 kg ha-1) in most of the soils. Majority (93.3%) of the soils showed adequate sulphur (> 5 mg kg-1) before and after the floods.
The relative soil quality index ranged from 32.5 to 62.5%. Majority (80%) of the soils had low soil quality index and the remaining had medium soil quality index. Mulakuzha panchayath recorded the highest soil quality index followed by Chenganuur while Venmony showed the lowest. With regard to land quality index, 60.1 % of soils fall under very low category while 37.33 % under low category. Chengannur municipality recorded the highest LQI followed by Mulakuzha panchayath while Venmony recorded the lowest. Nutrient index for organic carbon and nitrogen were medium and low in all panchayats. Nutrient index for phosphorous was low in Venmony panchayath while it was medium in all other panchayaths. Nutrient index for potassium was high in Ala and Mulakuzha panchayaths and medium in other panchayats.
The results of the study reveal strongly acidic to extremely acidic soils in majority of the flood affected areas of AEU 9. Organic carbon, available phosphorous, potassium and sulphur levels increased while widespread deficiency of nitrogen and calcium were observed in majority of the panchayats. The entire study area showed deficiency of magnesium and boron. The results outline the need for regular liming to control soil acidity and to alleviate calcium deficiency. The soils should be supplemented with nitrogen, magnesium and boron to improve soil quality and to sustain productivity.