Assessment of soil quality in the post flood scenario of AEU 13 in Palakkad district of Kerala and mapping using GIS techniques

Abstract

Soil quality is the capacity of the soil to function within its ecosystem boundaries to sustain biological productivity, maintain environmental quality and promote plant and animal health. It primarily depends on its dynamic properties which significantly change under environmental disturbances. The flood of August 2018 witnessed by Kerala not only caused havoc to life and properties but also triggered alarming changes in soil quality. Two types of flood damages were noticed throughout the state either due to river overflow and water logging or by caustic landslides. The parts of AEU 13 (Northern foothills) in Palakkad district consisting of low hills with undulating topography was affected both by river overflow and landslides. The study area in AEU 13 comprises of ten panchayats belonging to Mannarkkad and Sreekrishnapuram block panchayats. Heavy overflow of Nellippuzha, Kunthippuzha and Kanjirappuzha rivers in the area caused destruction of field crops and sand and silt deposition on their banks. Landslides from Kalladikkodan and Anangan hills resulted in complete demolishment of the nearby areas in Karimba, Kottopadam and Kanjirappuzha panchayats. The present study was undertaken to assess the soil quality in the flood affected areas of AEU 13 in Palakkad district and to develop maps on soil characters and quality using GIS techniques. The soils of AEU 13 are poor in organic matter, strongly acidic, dominated by low activity clays and sesqui-oxides and suffer from multi-nutrient deficiencies. One hundred and one georeferenced soil samples were collected from the flooded and landslide affected areas, processed and analyzed for different chemical, physical and biological properties. The results showed variation in all soil attributes except in available B, exchangeable acidity and electrical conductivity. The bulk density ranged from 1.11 Mgm-3 to 1.69Mgm-3 with 54 percentage of samples coming above 1.4 Mgm-3. Regarding particle density, seventy five percentage of the samples had values greater than 2.4 Mgm-3, whereas porosity and water holding capacity were in an optimum range. All the samples were acidic with pH ranging from 3.9 (Alanallur) to 6.8 (Mannarkkad), but with low exchangeable acidity. Soil organic carbon varied from 0.38 (Mannarkkad) to 1.78 percent (Kottopadam) with40percentage of samples coming under low category. Seventy five percentage of the samples were low in available N with an average value of 238.2 kg ha-1 for the area. The available P and K were high in the area with 67 and 74 percentage of samples coming under high category for available P and K respectively. Available Ca was sufficient (>300 mg kg-1) in 70 percentage of samples while available Mg was deficient (<120 mg kg -1) in 60 percentage of the soil samples. All the soils were sufficient in available Fe, Mn, Cu and Zn whereas 99 percentage of samples were deficient in available B. Effective cation exchange capacity of the selected area was also low with an average of 8.4cmol kg-1. Thirty three percentage of the soil samples had dehydrogenase activity less than 75 μg TPF g soil-1day-1. The nutrient index of the AEU 13 in Palakkad district was low (<1.67) with respect to organic C and available N and high (>2.33) with respect to available P and K. Pearsons correlation matrix showed a strong positive correlation between organic C and available N and negative correlation between OC and bulk density. Soil pH is negatively correlated with exchangeable acidity and positively correlated with available Ca, Mg and K. When compared with the pre-flood analytical data collected from District Soil Testing Laboratory (DSTL), Pattambi, proportion of soil samples coming under medium and high category of soil organic carbon increased after flood, which may be due to organic matter deposition. There was a reduction in available Ca and Mg after flood which might be due to leaching and infiltration loss. The pre-flood data collected as well as the analytical results of the present study indicated deficiency of B and sufficiency of cationic micronutrients like Fe, Cu, Mn and Zn in AEU 13. Assessment of the present status of the land slide affected soils indicated higher bulk density and particle density than that of flood affected soils of the study area which may be due to the addition of heavier minerals during land slide from subsurface areas to topsoil. Available S, Fe and Mn were also higher in soil samples collected from landslide affected areas. For developing minimum data set (MDS), principal component analysis (PCA) was performed for 22 attributes and resulted in seven principle component groups. Soil quality index (SQI) was worked out using non linear scoring method. The MDS comprised of eight attributes with available Ca and bulk density having highest contribution to SQI. Soil quality index ranged from 0.408 (Karimba) to 0.539 (Kumaramputhur). The average relative soil quality index (RSQI) of flood affected soils of AEU 13 in Palakkad district was 43.92 percent which is rated as low. Only 20 % of the soil samples collected from the area had medium RSQI values. When averaged over different panchayats, Alanallur (48.67 percent) had highest and Karimba had lowest RSQI (37.36 percent). High bulk density and particle density and low available N and B might be the reason for low soil quality observed throughout the area. The soil quality of the post flooded soils in the AEU 13 can be improved by adopting appropriate soil health management strategies with major thrust on site specific and integrated nutrient management practices.