Browsing by Author "Santhosh, C"

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Availability indices of potassium in an ultisol under coleus cultivation
(Department of Soil Science and Agricultural Chemistry, College of Horticulture, Vellanikkara, 2007) Santhosh, C; Mariyam, K A
A field experiment was carried out in the main campus of College of Horticulture, Kerala Agricultural University, Vellanikkara to study the availability indices of potassium in an Ultisol under the coleus cultivation. The experiment was laid out in a randomized block design with eight treatments and three replications. The treatments consisted of eight different levels of potassium. All other crop management practices were done uniformly in all plots as per the recommendation of KAU. Observations on biometric parameters as well as yield attributes were recorded during the cropping period. The soil, shoot and tuber were analysed for the various nutrients. The quantity of potassium extractable by various reagents was also estimated at these three stages. The Q/I parameters were estimated for the soil under study and the thermodynamic parameters related to K supplying power of soil were worked out. Tuber number and tuber yield were significantly influenced by the potassium application up to 60 kg K2O ha-1. The size of the tuber was not significantly affected with potassium application. Available potassium status that increased linearly with the levels of K did not affect the availability of P where as availability of N increased during the active growth stage of the coleus. Available potassium increased significantly with the levels of K application. Availability of exchangeable Al and Mn in soil got reduced with the increased levels of K. Even though the nitrogen and potassium content in shoot increased with the levels of K application at active stages of crop growth it had not reflected in the final yield. Calcium and aluminium absorption were found to reduce with increase in available K. Nitrogen and phosphorous content in the tuber reduced towards the harvest of crop. Calcium and magnesium content in tuber was influenced by K application where as K content in tuber was not increased with the levels of K. At all stages of analysis the quantity of K extracted with all reagents increased with the levels of potassium application in the soil. The water soluble, exchangeable and non-exchangeable potassium were reduced from initial stages towards harvest indicating the crop utilization and the presence of dynamic equilibrium between the various forms of potassium. Correlation studies conducted between yield attributes and quantity of K extracted revealed positive correlation between tuber yields and tuber number with water soluble and exchangeable K. The quantity-intensity parameters estimated at temperatures viz. 25°C and 40°C showed that the desorption of potassium is more at higher temperature indicating the higher availability of K in summer season. The potassium adsorption of soil under study followed the Freundlich adsorption isotherm both at 25°C and 40°C.
Chemistry and transformation of boron in soils of Kerala
(Department of Soil Science & Agricultural Chemistry, College of Horticulture, Vellanikkara, 2013) Santhosh, C; Sureshkumar, P
Sixty five representative soil samples from 23 agro ecological units under five agro ecological zones of the state were collected and characterised with respect to the available boron status for the present study on “Chemistry and transformation of boron in soils of Kerala”. The samples were characterised for pH, EC, CEC, PBS, exchangeable cations, total sesquioxide and available nutrient status (organic carbon, P, K, Ca, Mg, S, Fe, Mn, Zn and Cu) along with available boron.. Among these soils 18 per cent of samples which included samples from southern and northern coastal sandy plains were deficient in boron (< 0.5 mg kg-1) while the acid saline soils of Pokkali and Kaipad have recorded highest levels of available boron (> 3.0 mg kg-1). The availability of boron was found to increase with soil acidity and electrical conductivity. Thirty one soil samples selected from 65 characterised samples representing all the AEUs and ensuring variability in physico-chemical properties and available boron were subjected to fractionation of soil boron. The different fractions, readily soluble, specifically adsorbed, organically bound, oxide bound and residual boron accounted a mean status of 0.59, 0.86, 1.79, 2.31 and 94.45 per cent of total boron respectively in soils of different AEUs in Kerala. All the fractions except residual boron were significantly and negatively correlated with soil pH, and positively correlated with electrical conductivity. The oxide bound and residual boron were highly positively and significantly correlated with the content of sesquioxide and clay and the organically bound boron was significantly correlated with organic carbon content indicating the influence of organic matter, oxides and hydrous oxides dominated amorphous clay minerals of tropical soils in retention and solubility of boron. Among the six soils included for adsorption studies (lateritic soil from Pattambi, wet land soil from Elavampadam, sandy soil from Onattukara, black cotton soil from chittoor, Kole land soils from Thrissur and Kayal land soil from Kuttanad), only two soils ie. Onattukara and Kayal land soils followed Langmuir adsorption isotherms at 250C. The adsorption data for all the soils except Onattukara sandy soil could be fitted in to Freundlich adsorption isotherm both at 25 and 400C. The amount of boron adsorbed at unit equilibrium concentration ( Freundlich K: KF) decreased with increase in temperature from 25 to 400C. The intercept of Quantity-Intensity curve decreased to negative values at higher temperature indicating desorption of boron from the sites when solution concentration fell below equilibrium concentration. The decrease in free energy with a positive enthalpy and a positive entropy in Pattambi, Elavampadam, Onattukara and Kole soils revealed that the adsorption of boron were spontaneous and endothermic. The reverse was the case with black soils of Chittoor and Kole land soils where adsorption was exothermic and non spontaneous. The incubation experiment conducted for a period of three months with different levels of organic matter and borax in three soils ie. Onattukara sandy, lateritic upland and low land of Elavampadam revealed the clear role of organic matter in adsorption, retention and release of boron. Either organic matter or borax independently could increase available boron substantially after one month of incubation and maintained almost a constant level during the further course of incubation. However higher levels of organic matter reduced the available boron after one month incubation as a result of adsorption by organic matter. At highest level of organic matter and borax (15 t and 12 kg ha-1 respectively), adsorption of boron was highest. The field experiment to optimize the boron nutrition for rice in low land lateritic soils in central Palakkad plains (Elavampadam) revealed the clear role of boron in improving the productivity of tillers, number of grains per panicle, thousand grain weight and ultimately yield. The response curve fitted to find out the optimum dose of boron for grain yield showed that application of borax @ 5.5 kg ha-1 would result in yield improvement to the tune of 1 t ha-1. The fractionation of soil boron at panicle initiation and harvest stage indicated that both readily soluble and specifically adsorbed boron in soil increased with the levels of borax up to 6 kg ha-1 while the other fractions increased linearly with the levels of borax up to 12 kg ha-1. The correlation studies and path analysis clearly indicated that plant absorption of boron mainly take place from readily soluble, specifically adsorbed and organically bound boron in that order due to the existence of dynamic equilibrium between these fractions.
Land use effects on soil organic matter in Manali watershed of Thrissur district, Kerala
(Department of Soil Science and Agricultural Science, College of Agriculture,Vellanikkara, 2025) Nasila, N; Santhosh, C
Soil Organic Matter is fundamental to the vitality of terrestrial ecosystems, underpinning nutrient cycling, soil fertility, and the equilibrium of microbial communities. Its composition and abundance are intricately shaped by environmental variables and anthropogenic activities, notably land-use practices. A nuanced comprehension of these influences is indispensable for formulating effective soil management strategies. The study "Land Use Effects on Soil Organic Matter in Manali Watershed of Thrissur District, Kerala", investigates the ramifications of various land-use systems on the composition, quality, and quantity of SOM. This research highlights pathways to sustainable land stewardship by exploring the relationship between land use systems and soil health. Soil samples were collected from six major land-use systems in the Manali watershed: natural forest, rubber, coconut, rice, banana, and nutmeg with four samples from each system, and analyzed for their physicochemical and biological properties. Various soil carbon fractions, including total organic carbon, labile carbon, particulate organic carbon, microbial biomass carbon, and mineralisable carbon, were measured. Forest soils had the highest carbon fractions and microbial activity, indicating superior organic matter content and biological health. In contrast, nutmeg and banana soils had the lowest. Forest soils recorded the highest Carbon Pool Index (1.92), Carbon Lability Index (0.93), and Carbon Management Index (174.65), reflecting enhanced carbon stability, while nutmeg and banana soils showed the lowest values. The study revealed strong interconnections between soil physicochemical, biological, and carbon fraction properties. Soil organic carbon showed positive correlations with total nitrogen (0.821***) and soil aggregation (0.686***), underlining its importance in nutrient retention and structural stability. Biological properties, such as enzyme activities and microbial populations, were closely linked with carbon fractions, including total organic carbon, microbial biomass carbon, particulate organic carbon, and labile carbon, emphasizing the central role of organic matter in supporting microbial activity and nutrient cycling. Total nitrogen also correlated positively with microbial populations and enzyme activities, highlighting its role in soil metabolism. Additionally, microbial activity was associated with soil aggregation, suggesting its contribution to maintaining soil structure. The strong interrelationships among carbon fractions indicate their collective influence on organic matter stability and nutrient availability. Humic acid and humin fractions were extracted and purified from soil samples to evaluate the impact of different land-use practices on soil organic matter stability. The findings revealed that forest soils yielded the highest levels of humic acid at 23.96 g kg⁻ ¹ and humin at 16.48 g kg⁻ ¹, highlighting their superior organic matter stability. Conversely, soils from banana and nutmeg plantations showed the lowest yields, highlighting the significant influence of land-use practices on soil quality. Additionally, forest soils had the highest proportion of humic acid, while rubber plantation soils exhibited the lowest. Humin content varied across land uses, with coconut soils containing the highest percentage and rubber plantations the lowest. The chemical characterisation of soil humic acid across various land use systems revealed notable differences in acidity and elemental composition. Rice systems recorded the highest levels of total acidity, reaching 11.13 meq/g, along with carboxylic groups at 4.57 meq/g and phenolic groups measuring 6.56 meq/g, while rubber soils exhibited the lowest values, indicating significant variability in humic acid properties. Elemental analysis also showed variation, with the forest system containing the highest concentrations of carbon, hydrogen, nitrogen, and sulphur, suggesting a richer organic matter content. In contrast, banana soils had the lowest elemental levels, whereas rice and rubber soils maintained moderate compositions. The carbon to nitrogen (C/N) ratio peaked in banana soils at 22.99, followed closely by coconut soils at 22.36. In contrast, forest soils had the lowest ratio of 17.26, reflecting differences in organic matter quality and potential decomposition dynamics among the land use systems. The structural characterization of soil humic acid was conducted using UV-VIS, VIS-IR, FTIR, fluorescence, and Raman spectroscopy. The UV-Vis spectra showed a distinct peak between 221 and 226 nm, followed by a steady exponential decline from 230 to 700 nm. Absorption coefficient ratios varied, with the lowest E2/E4 (5.05) and E2/E6 (25.73) ratios in forest soils, and the highest in rice (6.99) and rubber (32.80) systems. The E4/E6 ratio ranged from 4.59 in rice to 5.12 in rubber. VIS-IR spectra exhibited a general decrease in absorbance with wavelength. Forest soils had the highest absorbance at lower wavelengths, indicating greater concentrations of organic chromophores in forest soil humic acid and increased activity in the visible and near-infrared regions. FTIR spectra showed broad peaks in the high-wavenumber region (4000–3000 cm⁻ ¹) and sharp peaks in the fingerprint region (1500–400 cm⁻ ¹), indicating functional group variations such as C=O, COOH, –OH, and C=C across systems. Fluorescence spectra showed a broad emission peak near 450 nm, with rice soils displaying the highest intensity, suggesting higher humification. Raman spectra revealed diverse vibrational modes, with coconut and rubber soils showing the most complex patterns. These findings highlight significant structural differences in humic acid across land-use systems, emphasizing the impact of land management on soil organic matter characteristics. The electrochemical properties of soil humic acids varied notably across land use systems, particularly in surface charge and particle size. All systems showed negative zeta potentials, with rubber plantations showing the highest negative potential of –66.25 mV, followed by forest soils at –61.50 mV, and banana plantations at –60.20 mV, indicating strong colloidal stability. Average particle sizes ranged from smaller in rice soils (354.50 nm) to larger in forest soils (1739.05 nm), reflecting differences in aggregation and structure. This study underscores the profound influence of land use systems on the composition, quality, and stability of soil organic matter. Forest soils exhibited the highest carbon fractions, microbial activity, and enzymatic functions, indicating superior soil health, while banana and nutmeg soils recorded the lowest. Humic acids varied in composition, acidity, and elemental content, with forest soils demonstrating the highest organic matter stability. Spectral and electrochemical analyses revealed differences in structural characteristics, surface charge, and particle size, reflecting variations in soil aggregation. These findings highlight the impact of land use practices on soil organic matter dynamics and emphasize the need for sustainable management to enhance soil quality and fertility.