Positive ions that are available in soils absorb on grain surfaces. The total sum of cations that can be absorbed bij a soil/sediment at a certain PH is defined by the cation-exchange capacity (CEC, in meq g-1: mol equivalents per gram). The uptake of cations is an important parameter in agriculture and the larger the CEC, the more cations can be absorbed to the soil. The CEC depends highly on the pH of soil and sediments, where the CEC decreases with decreasing PH (increasing acidity). The exchange of ions on sediments occurs commonly fast on geological time scales, but the kinetics of adsorption in natural environments is still poorly understood. The strength of the bonding between the cations and the sediments varies from weak Van der Waals bondings (physical adsorption) to strong chemical bonds. The CEC is widely used for agricultural assessment because it is a measure of general soil fertility as well as an indicator of structural stability because CED is capabel of enhancing development of shrinkage cracks. The list below shows the CEC for different types of minerals. The data indicate that the CEC can vary over 2 orders of magnitude for various types of , minerals and can vary one order of magnitude within one soil type. Cation exchange capacity for different types of sediment (Eisma, 1992; Locher and de Bakker, 1990):

Cation exchange capacity.

/pdf/a-comprehensive-review-on-the-applications-of-coal-fly-ash-mt8gcj5phv.pdf

A comprehensive review on the applications of coal fly ash

Heavy metals in soils

https://stacks.cdc.gov/view/cdc/37676/cdc_37676_DS1.pdf

Toxicological Profile for Lead

Mineral Nutrition of Higher Plants, 2nd edition, H. Marschner. Academic Press, London (1995), 889, (ISBN 0-12-473543-6). Price: 29.95 Pound Sterling

A review of the distribution coefficients of trace elements in soils: Influence of sorption system, element characteristics, and soil colloidal properties

https://eprints.kingston.ac.uk/29349/1/Hooda_29349.pdf

Opportunities and challenges in the use of coal fly ash for soil improvements--a review.

Cadmium uptake by tobacco as affected by liming, N form, and year of cultivation.

Sorption of cadmium, nickel, and zinc in mono- and multimetal systems

The effects of sludge application on soil properties and cotton (Gossypium hirsutum L.) response were investigated in an Inseptisol in central Greece. Digested sludge was incorporated in the 0 to 15 cm soil depth at rates of 10, 30, and 50 Mg ha -1 , and repeated for four consecutive years. Sludge treatments were compared to an inorganic fertilizer application and an untreated control in a completely randomized design with four replications. Sludge application increased soil organic matter, associated nutrients and improved physical properties. However, soil electrical conductivity increased with increasing sludge application to levels that may affect growth of salt-sensitive crops and warns against long-term application that may impair essential soil functions. The multifold increase ofOlsen P and nitrate N beyond crop needs is a reason of concern for surface runoffand nitrate leaching below the root zone at the higher sludge application rates. Sludge application of 10 Mg ha -1 was sufficient to improve soil chemical properties with less risk of water contamination. Cotton responded to sludge application by increased nutrient uptake and yield, which indicated that sludge could replace inorganic fertilizer needs even at the lower application rate. However, fluctuations of nutrient uptake and yield between growing seasons were of greater magnitude than those caused by sludge application. Multiple regression analysis revealed that P uptake was the major limiting factor for determining cotton yield.

Christos D. Tsadilas

Papers

A review of the distribution coefficients of trace elements in soils: Influence of sorption system, element characteristics, and soil colloidal properties

Opportunities and challenges in the use of coal fly ash for soil improvements--a review.

Cadmium uptake by tobacco as affected by liming, N form, and year of cultivation.

Sorption of cadmium, nickel, and zinc in mono- and multimetal systems

Effects of Repeated Application of Municipal Sewage Sludge on Soil Fertility, Cotton Yield, and Nitrate Leaching