Browsing by Author "Lecuona, Antonius Ignatius"
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- ItemInfluence of a coal derived potassium humate on the yield and nutrient content of tomato (Lycopersicum esculentum L.) under field conditions(Stellenbosch : Stellenbosch University, 1997) Lecuona, Antonius Ignatius; Combrink, N. J. J.; Stellenbosch University. Faculty of AgriSciences. Dept. of Agronomy.ENGLISH ABSTRACT: The exact composition and physical properties of humic substances has not been clearly defined. humic substances are ubiquitous and are found in all soils. humic substance s are classified into humic acids, fulvic acids and humin on the basis of their solubility in water. The charateristics of humic substances also vary according to the extarction method. This makes the comparison between various types even more difficult. The importance of humic substances in plant nutrition has also been identified. Various elements are bund to humic substances which improve the soil nutritional status. Pesticides and herbicides are degraded or absorbed by humic substances which netralises these chemicals in the soil. It has been found that the relation between humic substances and microbial growth can have positive effect on plant growth. Although humic substances are resistant to microbial breakdown, there are some carbon compounds associated with humates that were readily decomposable. The most significant effects of humic substances have been found on root growth. It seems that roots react more readily that leaves and stems to applications of humic and fulvic acids. When humic acids are applied in low concentrations, its effect is more hormonal than nutritional. The humic substances with lower molecular mass have higher hormone-like activity then the high molecular humic subtances. A coal derived potassium humate was used in this study to determine the yield, quality and elemntal status of tomatoes under field condition. In the field study no significant differences in yield, quality or the elemental status of fruits and leaves were found. This was primarily ascribed to the high soil nutrient status and carbon content of the soil. The rate of potassium release from a coal derived potassium humate, a commercial potassium chloride fertilizer and soil alone was also determined under varying conditions. The rate of potassium release through diffusion in a soil with added potassium humate and without was higher than soils added with a commercial availbale potassium chloride. When the leachate of soil water was measured, the soil with the commercial pottasium chloride had the highest rate of potassium release. The release of potassium was also measured varying the tempreature and total amount of water. At lower temperatures more potassium was released than the higher temperatures and the lower water volumes released more potassium than the higher water volumes at all tested temperatures.