Are you an EPFL student looking for a semester project?
Work with us on data science and visualisation projects, and deploy your project as an app on top of Graph Search.
Concept
Residual sodium carbonate index
Summary
The residual sodium carbonate (RSC) index of irrigation water or soil water is used to indicate the alkalinity hazard for soil. The RSC index is used to find the suitability of the water for irrigation in clay soils which have a high cation exchange capacity. When dissolved sodium in comparison with dissolved calcium and magnesium is high in water, clay soil swells or undergoes dispersion which drastically reduces its infiltration capacity.
In the dispersed soil structure, the plant roots are unable to spread deeper into the soil due to lack of moisture. However, high RSC index water does not enhance the osmotic pressure to impede the off take of water by the plant roots unlike high salinity water. Clay soils irrigation with high RSC index water leads to fallow alkali soils formation.
RSC is expressed in meq/L units. RSC should not be higher than 1 and preferably less than +0.5 for considering the water use for irrigation. The formula for calculating RSC index is:
RSC index = [HCO3 + CO3] − [Ca + Mg]
RSC index = HCO3/61 + CO3/30 – Ca/20 – Mg/12 (in case the ionic concentrations are measured in mg/L or ppm as salts)
While calculating RSC index, the water quality present at the root zone of the crop should be considered which would take into account the leaching factor in the field. Calcium present in dissolved form is also influenced by the partial pressure of dissolved at the plants root zone in the field water.
Soda ash [Na2CO3] can be present in natural water from the weathering of basalt which is an igneous rock. Lime [Ca(OH)2] can be present in natural water when rain water comes in contact with calcined minerals such as ash produced from the burning of calcareous coal or lignite in boilers. Anthropogenic use of soda ash also finally adds to the RSC of the river water.
Where the river water and ground water are repeatedly used in the extensively irrigated river basins, the river water available in lower reaches is often rendered not useful in agriculture due to high RSC index or alkalinity.
About this result
This page is automatically generated and may contain information that is not correct, complete, up-to-date, or relevant to your search query. The same applies to every other page on this website. Please make sure to verify the information with EPFL's official sources.
Related lectures (8)
Soil Sciences: Main Soil Types in Switzerland
Covers the main soil types in Switzerland and their fertility and ecological functions.
Chemical Equilibria in Environmental Chemistry
Provides a comprehensive review of environmental chemistry concepts, including carbonate/alkalinity, redox, metal speciation, and kinetics.
Water Quality Modelling: EC, Alkalinity, Hardness, Carbonate Chemistry
Explores EC, alkalinity, hardness, and carbonate chemistry in water quality modelling, emphasizing measurement methods and ion relationships.
Related concepts (3)
Alkali soil
Alkali, or Alkaline, soils are clay soils with high pH (greater than 8.5), a poor soil structure and a low infiltration capacity. Often they have a hard calcareous layer at 0.5 to 1 metre depth. Alkali soils owe their unfavorable physico-chemical properties mainly to the dominating presence of sodium carbonate, which causes the soil to swell and difficult to clarify/settle. They derive their name from the alkali metal group of elements, to which sodium belongs, and which can induce basicity.
Environmental effects of irrigation
The environmental effects of irrigation relate to the changes in quantity and quality of soil and water as a result of irrigation and the subsequent effects on natural and social conditions in river basins and downstream of an irrigation scheme. The effects stem from the altered hydrological conditions caused by the installation and operation of the irrigation scheme. Amongst some of these problems is depletion of underground aquifers through overdrafting.
Hard water
Hard water is water that has high mineral content (in contrast with "soft water"). Hard water is formed when water percolates through deposits of limestone, chalk or gypsum, which are largely made up of calcium and magnesium carbonates, bicarbonates and sulfates. Hard drinking water may have moderate health benefits. It can pose critical problems in industrial settings, where water hardness is monitored to avoid costly breakdowns in boilers, cooling towers, and other equipment that handles water.