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ThesisItem Open Access Status, availability and transformation of magnesium in acid soils of Kerala(Department of Soil Science and Agricultural Chemistry, College of Horticulture, Vellanikkara, 1992) Prema, D; KAU; Jose, A IThe investigation consisted of four parts, namely (1) magnesium status of soils in Kerala (2) evaluation of laboratory indices of Mg availability (3) transformation of applied Mg in soil and (4) pattern of Mg uptake by banana from different sources at different levels. In Part I, one hundred and fifty surface samples were collected from all over the State of Kerala, to study the status of Mg as well as properties in relation to the behaviour of Mg in these soils. In part 2, some selected chemical agents were tried in twenty selected soils in order to evolve a suitable extractant for available Mg. In Part 3, two acid rice soils of Kerala namely, Karappadam and laterite were incubated at field capacity for a period of 180 days with and without the addition of magnesium sulphate, magnesite and dolomite at the rate of 1250, 2500 and 3750 kg MgO ha-1, to monitor the pattern of release of Mg from applied sources . Soil samples were drawn regularly at 15 days interval for the determination of available Mq and at 60 days interval for the determination of other important chemical properties. In Part 4, a field experiment of banana was conducted to study the response to applied Mg.ThesisItem Open Access Standardisation of plant part as an index of potassium status in banana, musa (AAB Group) nendran(Department of Soil Science and Agricultural Chemistry, College of Agriculture, Vellayani, 1994) Sumam George; KAU; Padmaja, PA field experiment in Musa (AAB group) Nendran, the most popular commercial fruit crop of Kerala was undertaken from August, 1991 to May, 1992 with seven graded levels of K as treatments replicated thrice. The soil, medium in N and P and high in K status belonged to the taxonomic class ‘loamy kaolinitic isohyperthermic aeric tropic fluvaquents’. The effects of higher levels of K on all important growth characters of the crop like height of pseudostem, girth of pseudostem at different heights from the ground level, total number of leaves, number of functional leaves, total leaf area, leaf area index and total dry matter production were more pronounced from the shooting stage of the crop after the plants had received the full dose of K supply. Uptake of major nutrients N, P and K showed increasing trend with increase in K supply. Uptake of Ca showed a negative relationship with increasing K application while Mg uptake showed an inconsistent pattern. Uptake of micronutrients Fe, Mn, Cu and Zn were maximum at K3 level of application (225 g K2O plant-1). Soil content of available K increased while exchangeable Ca and Mg contents decreased at higher levels of K supply. The maximum bunch yield of 26.18 t ha 1-which was significantly higher than all other treatments was recorded at K3 level (225 g k2O plant-1) This level also resulted in maximum values for all the yield attributing characters like number of hands bunch-1, number of finger bunch-1, weight of hand, length of finger, girth of finger and weight of finger. By adopting this recommendation a net fertilizer saving of 75g K2O plant-1 Can be achieved which is equivalent to 312.5 kg of muriate of potash costing Rs. 2000 at the present market rate. Over and above this, increase in yield obtained by doing so is 4500 kg ha-1. Additional income that could be generated by the way of sale of this at the rate of Rs. 8 kg-1 works out to Rs. 36000. Thus a total saving of Rs. 38000 ha-1 can be achieved by following the suggested recommendation. Path coefficient analysis of yield attributes showed that the character number of finger bunch-1 is having the maximum direct effect on yield followed by girth of fruit and weight of fruit. Quality characters of the fruit namely total and non reducing sugars, shelf life and flesh peel ratio showed significant and positive trend towards K nutrition. Correlation coefficient were worked out between bunch yield and important crop characters. Balance sheet of nutrients in soil after harvest of the crop was worked out to assess the final soil status of nutrients in relation to the initial status. Petiole of the third leaf up to shooting stage of the crop and that of the flag leaf there after was selected as the index of K status of the plant as the K content of the same was found to hold the maximum relationship with bunch yield at all the growth stages. The critical K levels in the petiole for maximum yield as well as maximum response to fertilizer application at each stage were determined which were found to be 1.30 per cent and 1.02 per cent respectively at early vegetative stage, 1.28 per cent and 1.06 per cent respectively at late vegetative stage, 1.80 per cent and 1.36 per cent respectively at shooting stage, 2.43 per cent and 1.98 per cent respectively at post shooting stage, 2.50 per cent and 1.80 per cent respectively at bunch maturation stage and 2.47 per cent and 1.80 per cent respectively at harvest stage. The critical K content in soil for economic yield worked out to 286.5 kg K2O ha-1 at early vegetative stage, 276.5 kg K2O ha-1 at late vegetative stage, 271.o kg K2O ha-1 at shooting stage, 239.o kg K2O ha-1 at post shooting stage, 245.0 kg K2O ha-1 at bunch maturation stage and 236.0 kg K2O ha-1 at harvest stage. Graphs were plotted relating petiole K content to soil K content at important growth stages of the crop based on quadratic regression models to provide information on soil K content at a particular stage if the petiole K content at that stage is known. Linear regression models were developed relating soil K content to fertilizer dose to find out the quantity of fertilizer to be applied to bring the soil level to the critical level.ThesisItem Open Access Electro-chemical properties of selected oxisols and ultisols of Kerala with special reference to charge characteristics and surface mineralogy(Department of Soil Science and Agricultural Chemistry, College of Agriculture, Vellayani, 1992) Rajendran, P; KAU; Subramonia Iyer, RA study has been conducted in seven selected profiles of Oxisols and Ultisols representing the important pedological units with a wide geographical distribution in the state to have a deeper insight in to the electro-chemical behaviour of these soils. A multipronged approach to the studies made are highlighted to enable a clear understanding of the achievements as against the major objectives and approaches made. A laboratory study with thirty six samples from seven profiles representing six Ultisols and one Oxisol has been carried out. Path coefficient analysis of important thirteen charge contributing factors against two parameters for measurement of charge and the inter-relationship of 15 soil characters show that organic matter5, clay %, R2 O3%, Alo% and Feo% are the major factors that control the surface charge behaviour of the soils. The factors studied explained only 55% and 48% of the variability of cation exchange and anion exchange respectively. Study of the distribution of the electric charges in the surface and sub- surface horizons of the soils was made by the means of potentiometric titrations and by measurement of adsorption of ions in the presence of varying concentration of electrolytes. The titration curves at different ionic strengths crossed at the common point intersection the zero-point of charge (zpc). Thus the electro-chemical behaviour of these soils was found to be similar to that exhibited by many metallic oxides in which the surface potential of reversible double layer is determined solely by the activity of potential determining ions, H+ and OH- in the bulk of the solution. The zpc for the surface horizons was found to be lower than the sub-surface and sub- surface horizons in all the soils studied. Soil to soil variation in zcp between surface and sub-surface horizons were more or less the same for all samples. Thus zcp can not be recommended as a taxonomic tool in soil classification to distinguish Oxisols from Ultisols. From known values of surface area and zpc of these soils, the values for net electric charge was calculated by the application of the Gouy- Chapman model of double layer and was found to obey the theory only at a critical electrolyte concentration. As the soils were found to be similar to that of constant potential systems, the charge distribution varied substan\tially with PH and electrolyte concentration. Direct measurement of adsorption of ions from solutions of KC1 NaCl and CaCl2 showed that the nature and valence of index cations also influenced the magnitude of the negative charges on the soils particles. On the basis of the influence of PHJ, electrolyte concentration and the valence of the counter-ions on the electric charges of the soils most of the conventional methods of ion-exchanged determinations using buffered electrolytes at high concentrations appears to be inappropriate for tropical soils. In a study for the evaluation of ion-exchange measurements it was found that the compulsive exchange methods is most suitable for the combined estimation of CEC and AEC. The traditional ammonium acetate method was found to give over estimations of CEC and thus very high values. Calcium chloride, 0.002 M was found to be equally effective but owing to the simplicity of the procedure, the former appeared better. The compulsive exchange method is free from the inherent defects of neutral normal ammonium acetate and hence would seem well suited for the Oxisols and Ultisols of Kerala. Although sesquioxidic components in combination with organic matter apparently dominate the charge properties of these soils, there was evidence from the titration curves to shows the presence of small amounts of clay minerals with permanent negative charge. This was confirmed by different methods and was found in good agreement with the estimated theoretical results. However under field conditions the expression of this constituent was minimum and the variable charge components such as Fe, al oxides certainly control the electro-chemical characteristics. In a separate experiment to find out the contribution of organic matter and sesquioxides towards exchanges properties of soils, it was observed that bout 64% of the negative sites and 8% of the positive was contributed from organic matter. Sesquioxides explained only 11% of the variablility in CECX and 22% of the variability in AEC. The combined effect of organic matter and R2O3 removal was highly significant with respect to CEC and AEC in all the soils studied. Mineralogical investigation revealed the presence of kaolinite as the dominant clay mineral. Appreciable amounts of smectities, quartz and gibbsite was also identified. The presence of smectities was not reflected in the CEC of any of the samples. Scanning electron micrographs did not give much information other than the presence of a thick coating of iron and amorphous materials over clay aggregates. The specific surface measured by ethylence glycol retention method invariably showed higher values than the determined values obtained for negative adsorption data. The specific surface determined closely followed the organic matter content of the samples inspite of the vertical increase in clay content with in profiles.