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1977 - 197911980 - 19881
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Subject: Soil Sciences × Author: KAU × End date: 1988 ×
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    ThesisItemOpen Access
    Investigations on the salinity problems of pokkali and kaipad areas of Kerala state
    (Department of Soil Science & Agricultural Chemistry, College of Agriculture, Vellayani, 1977) Samikutty, V; KAU; Aiyer, R S
    The saline soils of the State viz., Pokkali, Kaipad and Orumundakan are coastal saline soils, which cover an area of about 30,000 hectares, cropped to a single crop of paddy. The profile characteristics of the soil reveal that they are Entisols. They contain varying levels of soluble salts depending upon their nearness to sea, backwater, or their situation on the flood plains of rivers and their nearness to the river mouths. The electrical conductivity of the saturation extract (ECe) of these soils range between 7.6 to 226.3 mmhos/cm showing differences in the magnitude of salinity encountered, prior to the soils being leached in summer months. Though the soils are exhibiting extremely high levels of salinity in the summer months, they get decreased rapidly below critical levels for growing a successful saline resistant paddy crop by July-August. The observed SAR and ESP values ranging to the maximum values of 25.0 and 26.3 in the months of February-March rapidly get decreased to 1 to 3 by between August and November. These low levels of salinity are maintained till December-January with an occasional spurt in salinity levels dependent on the opposing hydrological situation caused by the flood and rain waters on the one hand from east to west and the tidal waters from the west to the east on the other. The long period of nearly six months, when salinity in the soils are below critical levels, indicate the possibility of introducing a two crop system instead of one, provided nurseries are raised in non – saline uplands and transplanting resorted to in the raised mounds: previously leached free of soluble salts during the monsoon. The cationic-anionic composition of the soils reveal that they are Na-Mg-Cl-SO4 type of coastal saline soils. About 50 per cent of the soils studied have a pH below 5.5 and 15 to 20 per cent of the soils have lime requirement of more than 5 tons per hectare. In general the soils are extremely poor in phosphates and rich in potash. Application of non-magnesium containing lime materials at the time of mounding and subsequent leaching together with basal application of phosphate prior to planting are likely to enhance the yields of paddy in these areas. In short, the methods of management are highly location-specific calling for intensified research. The occurrence of saline water in the pits between the mounds even during the cropping period indicates the possibility of mixed rice culture with pisciculture
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    ThesisItemOpen Access
    Studies on exchange equilibria and its prediction on some acid soils of Kerala
    (Department of Soil Science and Agricultural Chemistry, College of Horticulture, Vellayani, 1988) Swarnavi, S; KAU; Pushakala, S
    More than 70 per cent of the upland soils of Kerala are acidic. The acidity of the soil is primarily associated with the presence of hydrogen and aluminium in exchangeable form. The soil solution aluminium in acid soil infertility clearly establishes the agronomic significance of aluminium ion equilibria in soils. The present study, entitled “Studies on exchange equilibria and its prediction on some acid soils of Kerala” was conducted to find out(1) the effect of different concentrations of aluminium in the electrolyte solution on exchange equilibria in soils (2) the influence of different cations on the free energy and various selectivity coefficients (3) the dependence of different selectivity coefficients on potassium, calcium and magnesium saturation of soils (4) the role of organic matter on cation exchange equilibria with special reference to potassium, calcium, magnesium and aluminium. Cation exchange equilibria involving aluminium- potassium, aluminium – calcium and aluminium- magnesium were studied in three soil types, viz., Kari, laterite and redloam soils, differencing in their texture and organic matter content. The normalized exchange isotherms for different soils and cationic systems were drawn and the results were interpreted in terms of different selectivity coefficients and approximate free energy change of the exchange reactions. From the study on the effect of different electrolyte concentration of aluminium on aluminium – potassium, aluminium- calcium and aluminium – magnesium exchange, an increasing aluminium adsorption was observed with an increase in electrolyte concentration of aluminium. The adsorption of aluminium was maximum in soils with high organic matter content. The normalized exchange isotherms of aluminium for different cationic systems and soils lay above the diagonal, suggested the preferential adsorption of aluminium over other cations. Except the Gapon selectivity coefficient, all the other coefficients (KKDO, KV and KN) increased upto a certain value of base saturation and then decreased. The value of KG increased with increase in base satuation. Among the various selectivity coefficients, KN was found to be the most dependent one and KG the least dependent. The dependence followed the order KN > KV > KKDO > KG. The negative values of free energy change for different cationic systems suggested the preferential adsorption of potassium, calcium and magnesium over aluminium. Among these cations potassium was found to be adsorbed with more energy, followed by calcium, magnesium, and then by aluminium. The values of free energy change showed the following order of preference for the competing cations: K > Ca > Mg > Al. From the study it can be concluded that potassic fertilizers can be effectively used in acid soils of Kerala, because of its high retention and minimum leaching loss. Compared to potassium, calcium and magnesium were adsorbed with less bond energy and hence to maintain a higher concentration of these cations in the soil exchanger, a considerable amount of calcium and magnesium should be supplied by frequent application of lime. To evaluate correctly the response of applied potassic fertilizers and liming material in different soils, efforts should be made to relate exchange behaviour of potassium, calcium and magnesium to the nature and relative proportion of different soil clay minerals. Similarly, the extension of the predictive approach essentially meant for binary system need special attention in order to make the studies on cation exchange equilibria more realistic and field oriented.