The need to irrigate with waters high in sodium and soluble salts for use in agriculture has increased due to the understandable interest many societies have placed in storing fresh water resources – especially in areas with dry and semi-dry climates (Jalali & Ranjbar, 2009). Furthermore, disposing of nutrient-rich effluents to rivers, lakes and oceans can have serious environmental impacts such as water contamination and eutrophication (Balks et al., 1998). From these concerns arises the emerging trend to use wastewater (from agricultural, industrial or sewage sources) towards land applications (Halliwell et al., 2001). Although this solves the immediate concern of water body ...view middle of the document...
In addition to degraded soil structure and issues of surface and ground permeability, sodic conditions arising from effluent irrigation can also cause an increase in soil pH. This chemical change – among other factors – can cause soil microflora to undergo considerable stress. Soil microbial activity is responsible for maintaining a multitude of soil physical properties and processes. Decreases in the size and activity of soil microbial populations will result in a reduction of organic matter decomposition and nitrogen, carbon, sulphur and phosphate mineralization. The resulting soil solution, void of many essential plant nutrients, could lead to significant decreases in crop production and agronomic revenue. In fact for some crops such as sugarcane, the formation of soils high in sodium is considered the primary cause of yield declines and overall soil degradation. As such, any threat to the activity of soil microbes is of particular concern (Rietz & Haynes, 2003).
The following literature review will provide important background information pertaining to soil sodicity measurements and an overview of four soil physical properties/processes which have been suggested to be strongly affected by increases in soil sodium content: swelling/dispersion, erosion, microbial activity, and hydraulic conductivity + infiltration.
The exchangeable sodium percentage (ESP) and sodium adsorption ratio (SAR) are among the most common parameters used to measure soil sodicity (Halliwell et al., 2001). Understanding the nature of these parameters is therefore paramount in grasping the significance of experimental results related to soil sodicity. The ESP is defined as “the percentage of the cation exchange capacity occupied by sodium” (Balks et al., 1998) and is usually expressed by the equation:
ESP = 100 - CNa/CEC
where CNa is equal to the concentration of exchangeable Na+ and CEC is the cation exchange capacity; both in cmolc kg-1. Because calculating the ESP requires determining the sum of...