Influence of Silicon on Heavy Metals Uptake And Mobility, Yields, and Quality of Selected Leafy Vegetables in Kiambu County, Kenya
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Date
2021
Authors
Ngugi, Moses Mwangi
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Publisher
Kenyatta University
Abstract
Heavy metal contamination and accumulation on agricultural soils pose a great risk due to toxicity, toxic materials of multiple sources, and of non-biodegradable nature. Lead and cadmium have phytotoxic and toxic effects on plants and animals. Leafy vegetables accumulate the metals resulting in enrichment along the food chain. Contamination in agricultural soils significantly reduces crop yields. Silicon has beneficial effects in enhancing plant tolerance to biotic and abiotic stresses. Silicon is known to reduce the uptake of metal ions by forming complex metal ions and altering soil pH. It also precipitates metal ions, compartmentalizes metal ions in cell vacuoles or cell walls, and hence reduced translocation to shoots, and promotes activities of antioxidant enzymes. However, information on its benefits has not been adequately explored. The study aimed to determine the amelioration of silicon on lead and cadmium uptake, mobility, and concentration in plant tissues and to evaluate the influence of lead and cadmium on the growth and biomass of leafy vegetables. The experiment was carried in two field experiments and a greenhouse experiment. The greenhouse experiment treatments were: lead (Pb), Si (silicon), Cadmium (Cd), Pb+Si, Cd+Si, and control. It was designed in Split plot CRD, with leafy vegetable species as the main plot and treatments as subplots. The field experiment was carried at the Kenyatta University research farm, and treatments included Si application and control. It was arranged in Randomized Complete Block Design (RCBD). Data collected was subjected to ANOVA using R software version 4.0.2 package and where there were significant differences, mean separation was done with Tukey at P< 0.05. Cadmium and lead significantly reduced leafy vegetable growth and production. Cadmium application reduced root biomass by 53.04%, 63.32%, and 70.20% in amaranths, spinach, and kale respectively. Lead reduced by 54.11%, 55.76%, and 60.72% in spinach, amaranths, and kale when compared with controls respectively. Lead and cadmium reduced above ground biomass with 25% in leafy vegetables. Silicon application enhanced leafy vegetable biomass tolerance by 30% when compared with soils spiked with lead and cadmium. Vegetables accumulated lead and cadmium beyond WHO concentration limits in plant tissues. Cadmium transfer factor and mobility were higher than for Lead. Lead and cadmium transfer and mobility index were less than one (<1). Results showed a strong negative correlation between cadmium concentrations and growth parameters (R2>0.8). Pearson correlation coefficient also indicated a strong positive correlation between cadmium concentrations in soils and plant tissues of leafy vegetables. Leafy vegetable uptake, translocate and accumulate metal ions in plant tissues. Silicon application enhanced leafy vegetable tolerance to lead and cadmium, and reduced transfer and mobility of metal ions. The study recommends silicon application on lead and cadmium contaminated soils to alleviate metal ions toxicity and reduced accumulation on edible plant tissues.
Description
A Research Thesis Submitted in Partial Fulfillment of the Requirements of the Award of Master of Science Degree in Agronomy in the School Of Agriculture Enterprise Development, Kenyatta University
October, 2021.
Keywords
Silicon, Heavy Metals, Kiambu County, Kenya