Browsing by Author "Divya Vijayan, V"

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Geotechnical characterisation of lateritic soil profiles in midland and highland plateaus of Kerala
(Department of Soil Science and Agricultural Chemistry, College of Agriculture, Vellanikkara, 2023-04-13) Mridul , V; Divya Vijayan, V
The soils of highland and midland laterites in Kerala are unique in characteristics due to the various soil formation processes in the landscape. The midland laterites are often underlain by plinthite and contain appreciable quantities of gravel, which holds against supersaturation where as the highland laterites are devoid of plinthite. The hill zones of Kerala are witnessing frequent landslides during every monsoon. Landslides are induced by several factors and the soil-rainfall interacting process is one of the important processes, wherein the soil susceptibility increases landslide hazards by triggering slope failure due to the draining of water through infiltration, percolation and saturation of soil at an extreme level. Geotechnical properties / Atterberg limits are the basic measure of soil plasticity as a function of moisture variation. It includes the Plastic Limit (PL) which is the limit at which soil changes from semi-solid to plastic and the Liquid Limit (LL) which is the limit at which soil changes from plastic to liquid state as the water content increases. Atterberg properties of soil of a region depend on soil physico-chemical properties (soil textural dynamics, porosity, soil mineral types etc) which strongly influence landslides. To understand the physical and geotechnical properties of the laterite soils of hill and midland with respect to their behaviour on progressive saturation with water, the study “Geotechnical characterisation of lateritic soil profiles in midland and highland plateaus of Kerala” was carried out in the Department of Soil Science & Agri. Chemistry, College of Agriculture, Vellanikkara during 2021-22. The soil profiles for the study were collected from Mulagunnathukavu, Attoor and Kuranchery (AEU 10) of Thrissur district, Kokkayar, Koottikkal (AEU 14), Koottar and Pampadumpara (AEU 16) of Idukki district for elucidating morphological, physical, chemical and geotechnical properties. The results of the physico-chemical analysis showed that, the soils were acidic in reaction with values ranging from (4.78 to 6.53) in midland and (4.17 to 6.49) in highland laterites. The Cation Exchange Capacity (CEC) of the soils ranged from 6.2 to 15.3 cmol (+) kg-1 in midlands and 10.40 to 19.60 cmol (+) kg-1in highland laterites. Based on the morphological and physico-chemical properties, the midland and highland were classified under the order Ultisols. The dominant suborder in all the midland laterites was ustults and the dominant suborder of highland was humults except for the Kokkayar profile which was under the suborder ustults. Among the midland profiles studied the Mulagunnathkavu soil profile was unique with plinthite formation in the lower horizon and the soil contained appreciable quantities of gravel and clay per cent. The Atterberg limits of highland soil was higher compared to midland soil and it ranged from 31.62 to 54 per cent for liquid limit, 22 to 35 per cent for plastic limit and 6.79 to 23.61 per cent for the plasticity index. The Atterberg limits of midland soil ranged from 23.99 to 45 per cent for liquid limit, 18.55 to 29 per cent for plastic limit and 4.71 to 19 per cent for plasticity index. The higher value of Atterberg limits in the highlands can be attributed to the presence of more fine earth clays in the highlands compared to the midlands. Comparison of soil properties between midland and highland soil profiles for the surface and sub soil horizons showed significant differences in the soil properties like organic carbon, extractable iron oxides, exchangeable sodium, potassium, liquid limit and plastic limit, coarse sand, gravel per cent and bulk density. The per cent of coarse sand, gravel per cent and bulk density were higher in midland laterites compared to highland laterites and the content of organic carbon, extractable iron oxides, sodium, potassium, liquid limit and the plastic limit was higher for the highland soil compared to midland. A correlation between plastic limit and liquid limit with different soil properties of highland profiles showed that the clay has positive correlation and sand has a negative correlation with Atterberg limits. The random forest classification-regression model ranked clay as the most important variable affecting the plastic limit. The high clay content contributed to a directional arrangement of soil particles leading to the increase in weakly bound water increasing the plastic limit. The X-ray diffraction analysis results revealed that kaolin, gibbsite, feldspar, quartz and mica were found in both midland and highland laterites, which showed the different stages of weathering. Thus, it can be concluded that, the high rainfall, soft lateritic deposits, highly plastic clay and intensively weathered rocks, will saturate the entire mass and can cause loss of shear strength and this can be one of the reasons for landslides in highlands (AEU 14 and 16). The midland laterites (AEU 10) though it contains high illuvial clay the hard plinthite layer (hardened mix of iron bearing minerals with honeycomb structure and voids with kaolin) holds against supersaturation and resist clay movement. Thereby ensuring protection against landslides and piping in this AEU 10.
Geotechnical characterisation of lateritic soil profiles in midland and highland plateaus of Kerala
(Department of Soil Science and Agricultural Chemistry, College of Agriculture, Vellanikkara, 2023-04-13) Mridul, V; Divya Vijayan, V
Heavy metal contamination of laterites by accumulation of solid wastes
(Department of soil science and agricultural chemistry, College of horticulture, Vellanikkara, 2015) Divya Vijayan, V; Sushama, P K
A heavy metal is defined as a metal that has the atomic number and specific gravity greater than 20 and 5 Mg m-3, respectively. Heavy metals occur naturally in the soil environment from the weathering of parent materials and also as contaminants at the waste disposing sites. Though, the soil acts as a sink for the majority of heavy metals, the excess uptake of any one of them may limit the plant growth. In this background, the research work entitled “heavy metal contamination of laterites by accumulation of solid wastes” was undertaken during the period 2010-2014. The project aims to investigate the extent of distribution of heavy metals (As, Cd, Cr, Pb, Hg and Co) in waste dumping sites of laterite as influenced by soil and climatic conditions using geostatistical technique, to correlate the activity of major soil enzymes with the contents of heavy metals, to explore the potential of phytoremediation as well as aerobic and anaerobic methods of composting for the removal of heavy metals in solid waste and to evaluate the performance of amaranthus under different decontaminated methods adopted. In order to attain the objectives, four experiments were conducted. The effect of soil and climatic factors on heavy metal accumulation was examined with the collection of soil samples at quarterly intervals for a period of one year from two different waste disposal sites located at Laloor and Kalamassery. For the study on phytoremediation, the crops, vetiver, marigold and sunflower were experimented. Both the aerobic and anaerobic methods of composting were tried for the removal of heavy metals in another set of experiment. A pot culture study was also conducted to assess the growth of amaranthus under different decontaminated conditions. The salient findings are summarized as follows: The percentage distribution of Pb, Ni, Co, Cr and Hg at the different sites of Kalamassery revealed that Cr had the highest distribution followed by others. At Laloor, Pb was found to be dominant for the major dumping sites, whereas Cr at the non dumping site. The geo accumulation index for Hg was recorded as above one for all sites at Kalamassery. The average contents (mg kg-1) of Pb, Co, Ni, Hg and Cr was 15.58, 6.06, 43.18, 0.56, 107.9 at Kalamassery and 82.84, 7.79, 35.54, 0.42 and115.67 at Laloor, respectively. Heavy metal contents were found to be higher during summer than rainy season except for Cr and Cd. In general, soil enzyme activities were higher during quarter II of the sampling period. There was a positive correlation between Fe and urease (0.391*) and Pb and phosphatase (0.350*). The phytoremediation study with the three different crops (sunflower, marigold and vetiver) proved vetiver as a good phytostabilizer compared to others. Vetiver was found to be a translocator of Cr, since Ni, Pb, Co and Hg were mostly stabilized in the root. Marigold translocated all these heavy metals from soil except Co, and sunflower translocated Co, Ni and Cr except Pb. Bioconcentration factor (the heavy metal concentration in the plant/ the heavy metal concentration in the soil) was higher for vetiver compared to sunflower and marigold. Vetiver removed the heavy metals from the waste material in the order Cr>Ni> Co> Pb. Compared to aerobic composting, the anaerobic method proved to be better for the removal of heavy metals from the waste material collected from Laloor. The comparative performance of amaranthus grown in soil under different methods adopted for reducing heavy metal contamination showed that the yield was found to be the highest in the treatment with aerobic compost. The lowest yield was reported for amaranthus grown with phytoremediated material, followed by absolute control. The uptake of major nutrients also followed the same trend as yield. The heavy metal content was higher in the shoots of amaranthus grown with waste material and the accumulation followed the order Cr>Pb>Ni>Co>Hg. In all the treatments under study, the presence of Cr was more dominant in the post harvest soil compared to other heavy metals.
Plant diversity and microbial activity as a function of soil carbon stocks in selected homegardens in the midland laterites of Kerala
(Department of Silviculture and Agroforestry, College of Forestry, Vellanikkara, 2024-01-19) Athulya Tom; Divya Vijayan, V
In woody ecosystems, understanding the relationship between plant diversity, microbial activity, and carbon sequestration is crucial, particularly in the context of addressing climate change and promoting sustainable land management. Homegardens are traditional land use systems that evolved through the generation of crop intensification. Apart from the livelihood security and economic advantages, the homegardens play a vital role in delivering many ecosystem services. In this context, addressing the role of homegardens in terms of plant diversity, microbial activity, and carbon sequestration is essential for ascertaining their potential contributions to sustainable and environmentally friendly practices. With this background, the study was carried out to investigate the carbon flux in the soil aggregates and their functional relation with plant diversity and microbial activity in selected home gardens in the midland laterites at the College of Forestry during the period 2022-23. The research was conducted under five land use systems which include Small Homegarden (SHG 0.4ha), a Forest area (Fo) and Treeless open area (TrO) of the Agro Ecological Unit (North central laterite) of Kerala. The plant diversity of the various homegardens revealed that the Simpson index was high in the forest (0.90) and SHG (0.87) followed by MHG and relatively less in LHG (0.63). The result of the physico-chemical properties of the soil revealed that the bulk density was lower in the surface soil and increased with depth. The Mean Weight Diameter (MWD) indicated the structural stability of soil which depicted that the forest had MWD of 0.74 mm followed MHG (0.68mm) and SHG (0.63 mm) compared to an open area (0.57 mm). The available nutrient distribution in the land use systems showed a variable trend with available nitrogen and potassium higher in the forest followed by SHG due to high plant diversity and associated litter and root dynamics. The available phosphorus was higher in LHG and MHG compared to forest and SHG. Soil organic carbon per cent in the five depths under the landuse systems ranged from 3.78 to 0.09 per cent and depicted a significant difference between all the land use systems, greatly in the 0-20 cm depth, where forest reported high SOC followed by SHG. The SOC stock (Mg C ha-1) under different land use systems followed a trend of forest (202.21) > SHG (157.62) > MHG (135.79) > LHG (119.60) >TrO (24.29). Macroaggregates in the different land use systems were reported to have high carbon storage especially forest and SHGs compared to microaggregates or clay and slit fractions. The microbial studies of various land use systems indicated considerable variability. The bacterial populations were higher than actinomycetes and fungi in the different land use systems. Among the land use systems, forest had the highest microbial count and the bacterial and fungal population was on par with SHG. The seasonal variation of enzyme activities revealed higher dehydrogenase activity in forest followed by SHG. The microbial biomass Carbon (MBC) in the three homegardens was relatively good and on par with the forest. A random forest regression model was developed to understand the most important variable affecting soil carbon stocks and the result revealed that C: N ratio, followed by the Simpson index, clay and silt carbon influence the carbon stock. The hierarchical cluster analysis grouped the land uses into four clusters based on the Euclidian distance and average linkage method. The MHG and LHG were grouped into one cluster because of their similarity and all other land use remained as independent clusters. The SHG mimics forest, by the resemblance in numerous aspects, such as microbial activity, soil carbon stock, MBC, and enzyme activity. Thus, we can conclude that although SHG offer specific advantages due to the diverse plant species, efficient resource utilization and space optimisation, the overall sustainability and carbon sequestration potential of other homegardens classes can be improved with effective management practices. Homegardens can play a crucial role as a nature-based solution to mitigate climate change through various mechanisms that contribute to carbon sequestration, biodiversity conservation, and sustainable land management.
Soil carbon stock estimation and prediction of aggregate associated carbon under different land use systems in Palakkad central plain using reflectance spectroscopy
(Department of Soil Science and Agricultural Chemistry, College of Agriculture , Vellanikkara, 2025-01-09) Abdul Hadi, K; Divya Vijayan, V
The distribution of soil organic carbon (SOC) across various aggregates and its changes over time is crucial for monitoring carbon dynamics and optimising nutrient management. Reflectance spectroscopy is a fast, non-destructive and economical solution for estimating SOC in the soil. In this context, the present study was proposed to identify the potential of different land-use systems for the sequestration of SOC and distribution of SOC among various aggregates of selected land-use systems (LUS), where the selected aggregates were macroaggregate (> 0.25 mm), micro aggregate (0.25-0.053 mm) and clay and silt fraction (< 0.053 mm). It also aimed to evaluate the predictive potential of reflectance spectra for estimating SOC associated with soil aggregates. The study was conducted in the Department of Soil Science and Agricultural Chemistry, College of Agriculture, Vellanikkara during 2023-24. The selected land use systems were natural forest, coconut plantation, rubber plantation, vegetable field, and paddy field, in the Palakkad Central Plain (AEU 22). Georeferenced surface (sample no. = 9), subsurface soil samples (sample no. = 9) and one profile sample were collected from each land use system. A total of 105 samples were collected. The soil samples were pre-processed and analysed for the different physico-chemical properties, wet aggregate analysis, soil carbon stock (SCS) and SOC in aggregate fraction. A part of the macroaggregates and microaggregates obtained from wet sieving was utilised to record the spectral signatures. Prediction models were then developed using the SOC content of these aggregates as the dependent variable, while the spectroscopic bands corresponding to each aggregate type served as the independent variables. The raw spectra obtained from the spectroradiometer underwent four preprocessing steps viz logarithmic transformation, Savitzky-Golay filtering (SG), first-order derivative (FOD), and second-order derivative (SOD) before model development. Correlation analyses were then performed to identify the most relevant wavebands associated with SOC. It reduced the number of bands needed for modelling. The prediction of aggregate-associated SOC was performed using a Partial Least Squares Regression (PLSR) model. The efficiency of developed models was analysed using the coefficient of determination (R2), root mean square error (RMSE), and the ratio of prediction deviation (RPD). The subset prediction models were also developed to identify which region is best for prediction. Finally, the variable importance in the projection score (VIP) was used to find which wavelengths are contributing the most of the variance in the PLSR model. The result showed that the perennial systems such as forest (47.95 Mg ha-1) and rubber (43.08 Mg ha-1) showed higher soil carbon stock. In contrast, annual cropping systems like paddy (SCS = 16.55 Mg ha-1) and vegetable (SCS = 19.14 Mg ha-1) exhibited lower soil carbon stock. The distribution of water-stable aggregates revealed that greater proportion of macroaggregates in rubber (96.05 %) and forest systems (95.18%), followed by coconut (83.12 %). Lower aggregate fractions, including microaggregates and clay-silt fractions, were more abundant in paddy (micro aggregate = 30.72 %; clay and silt fraction = 2.29 %) and vegetable fields (micro aggregate = 26.60 %; clay and silt fraction = 2.53 %). Mean weight diameter was highest in forest (2.65 mm) and rubber systems (2.44 mm) and lowest in paddy (0.73 mm) and vegetable systems (0.99 mm). These findings suggest that intensive tillage and lower SOC levels significantly degraded soil structure. The key spectral bands for predicting bulk SOC spanned the entire spectrum (400–2500 nm), whereas bands relevant to aggregate-associated SOC were primarily located in the shortwave infrared (SWIR) region (1000–2500 nm). These findings indicate that bulk SOC predictions were more influenced by the chromophore effect, while aggregate SOC predictions depended on chemical bonds in specific spectral regions. The preprocessing steps influenced the prediction ability of the model. second-order derivatives (SOD) produced the best models for the prediction of microaggregate SOC (MiSOC) and macroaggregate SOC (MaSOC), while Savitzky Golay-filtered full spectra were most effective for bulk soil SOC. Prediction accuracy was higher for MiSOC (R² = 0.84, RMSE = 0.25, RPD = 2.21) compared to MaSOC (R² = 0.92, RMSE = 0.25, RPD = 1.74). The R2 value of the test dataset further validated the prediction efficiency of the model. The R2 value of the test dataset were 0.79, 0.66, and 0.84 for MiSOC, MaSOC, and bulk soil SOC, respectively. The superior predictive performance for MiSOC can be attributed to the higher organic carbon content in microaggregates and the difference in the type of organic functional groups between the two fractions. The result shows that spectroscopy can be effectively exploited for the prediction of aggregate-associated carbon