Soil and vegetation characteristics in the post flood scenario in selected tree based land use system in Thrissur, Kerala
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Date
2020
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Departmemt of Silviculture and Agroforestry, College of Forestry, Vellanikkara
Abstract
The unprecedented and intense nonstop rainfall for days together occurred in Kerala during August 2018 affected all the aspects of human lives including socio economic conditions, transportation, infrastructure, agriculture, and livelihood. Flooding lead to food crop shortages due to the loss of entire crop harvest and degradation of soil quality. The present study is aimed at identifying the impacts of Kerala flood 2018 on soil physico – chemical and biological properties, vegetation and soil seed banks along the ‘Kurumali’ river basin of Thrissur district of Kerala in five major land use systems prevalent in the area viz; forest, rubber, nutmeg and coconut plantations and open land. For this purpose, all five land use systems in flood affected and the same five land use systems in the adjacent area where flood has not been affected were selected. Soil samples were collected up to one meter soil depth (0-20 cm, 21- 40 cm, 41- 60 cm,61- 80 cm and 81- 100cm) for soil analysis after seven months of flood . Soil physical properties like soil bulk density, soil porosity and soil texture; and chemical properties like soil pH, EC, available N, P, K; secondary nutrients like Ca, Mg and Sulphur and micronutrients like Fe, Cu, Mn, Zn and Boron were analysed. The biological properties assessed were total microbial count (Bacteria, Fungi and Actinomycetes), dehydrogenase activity and microbial biomass carbon. Soil seed bank data were generated in two seasons (Pre- monsoon and post- monsoon of 2019) from the top soil of all the five land use system studied. In vegetation analysis diversity indices, abundance and dominance of species were worked out. The bulk density and porosity had a little effect due to flood in all land use systems while soil texture had changed from sandy clay loam to clay loam structure in forest flood affected system. In coconut, it is changed from loamy texture to sandy clay loam and in open, the change was from loamy sand to silty clay loam in the surface soil ie. 0- 20 cm depth. The pH had a significant increase after flood in forest and open land use system (0.31 and 0.26, respectively). The rubber and coconut flood affected systems had a significant decrease (0.16 and 1.34, respectively) in pH from flood non affected condition. The EC had a significant decrease after flood in rubber, coconut and open land use system (0.9dS m-1, 0.8 dS m-1 and 0.37 dS m-1 , respectively). The organic carbon content in forest, rubber and nutmeg flood affected land use system had showed a significant increase (0.2 %, O.8 % and 0.4 % , respectively) from flood non affected condition; whereas coconut and open flood affected land use system had showed a significant decrease in organic carbon (1.3 % and 0.7 % , respectively) from flood non affected condition. The forest flood affected had showed a significant increase (84kg ha-1) in available N from flood non affected condition. Rubber, nutmeg and open flood affected system had showed a significant decrease (201.6 kg ha-1, 35.7 kg ha-1 and 207.9 kg ha-1 , respectively) in available N from flood non affected condition. The effect of flood on available P also showed similar trend of OC at the soil depth of 0-20 cm. The forest, coconut and open flood affected land use system had a significant decrease (196.6 kg ha-1 421.5 kg ha-1and 125.8 kg ha-1 , respectively) in available K from flood non affected system. While rubber and nutmeg flood affected system showed a significant increase (299.4 kg ha-1and 292.0 kg ha-1respectively) in available K. The nutmeg plantation had a significant increase (9193 mg kg-1) while coconut plantation had significant decrease (1840.6 mg kg-1) in calcium content of soil after flood. Similarly the nutmeg plantation had a significant increase (174.1 mg kg-1) whereas coconut plantation had a significant decrease (131.4 mg kg-1) in magnesium content of soil after flood. The rubber plantation had a significant decrease (7.744mg kg-1) after flood in sulphur content of the soil. The forest had a significant increase (4.49 mg kg-1) in ‘Fe’ content after flood while open land use system had a significant decrease (5.43 mg kg-1) at the depth of 0- 20 cm. The forest, rubber and nutmeg had showed a significant increase (39.14 mg kg-1, 21.78 mg kg-1and 55.71 mg kg-1respectively) after flood in manganese content of soil at the depth of 0-20 cm. While coconut and open land use system had a significant decrease (60.22 mg kg-1and 19.39 mg/kg, respectively) in manganese content after flood. The rubber and nutmeg had a significant increase (40.46 mg kg-1 and 7.29 mg kg-1 , respectively) in copper content of soil after flood at the depth of 0-20 cm. Open land use system was also recorded with a significant increase (9.39 mg kg-1) in copper content of soil after flood at the depth 0- 20 cm. Forest, rubber and nutmeg plantation had a significant increase (1.07 mg kg-1, 2.13 mg kg-1 and 17.32 mg kg-1 , respectively) in zinc content after flood at the depth of 0-20 while, coconut and open land use system had a significant decrease (6.44 mg kg-1 and 1.56 mg kg-1 , respectively). Total microbial count (Bacteria, Fungi and Actinomycetes) had no significant difference after flood in any of the land use systems. With respect to the dehydrogenase activity, the entire four tree based land use systems remained without any appreciable change. The forest, rubber and nutmeg land use systems also had an increase (9.67g g-1, 64.48 g g-1 and 25.89 g g-1 respectively) in microbial biomass carbon after flood. While coconut and open land use system had a decrease (90.98 g g-1and 121.44 g g-1, respectively) in MBC after flood. Soil seed bank had no effect due to flood. The present study reveals that among the five land use systems, Forest land use system showed a comparatively neutral effect in some and a distinctive positive effect in most of the soil physico - chemical and biological properties after seven months of flood. The results implicated that the forest land use system was the least affected or reselient with respect to soil properties due to flood impact. The seed bank generated not showed any noticeable difference after flood. The flood has no serious effect on higher vegetation.
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