Soil salinisation: a local life cycle assessment impact category

Salinity is an increasing environmental problem in agricultural ecosystems and is not adequately represented in conventional life cycle assessment (LCA) impact categories. It is often not the total quantity of salts emitted or the proportion of salt accumulated in the soil profile that is the primary mechanism for deteriorating soil conditions for irrigated salinity, rather the ratio of major cations in the soil matrix and the potential for colloid dispersion and reduced permeability. A soil salinisation potential (SP) is proposed as an indicator for irrigated salinity and potential soil degradation from poor irrigation practices. The indicator uses the threshold electrolyte concentration concept that predicts the adjusted sodium adsorption ratio (SAR)/ Electrical conductivity (EC) ratio that soil will no longer flocculate, but potentially disperse. The SAR is converted to a threshold EC and compared to the measured EC in order to develop a site-specific irrigation equivalence factor (EF). This site/region/process specific EF is then used to weight the sodium load to soil and repeated for each stage throughout the entire life cycle to determine the overall Salinisation Potential (SP). The data required for calculating the SP is generally readily available either on site or from the water chemistry of the local watercourses. Preliminary calculations simply require the volume, pH, electrical conductivity (EC), alkalinity and the concentrations of Na, Ca, and Mg of the irrigation water. The site/process/region specific nature of the indicator ensures a quantitative measure to enable comparisons between different systems and is useful for identifying stages in the life cycle of a product (particularly food products), where the potential for soil salinisation and soil degradation is most severe.