Document Type : Research Paper
Authors
Abstract
Calcium and magnesium ions are two plant nutrients and are omnipresent in all natural systems. Calcium to magnesium ratio (Ca:Mg) is an important factor in evaluation of water quality for irrigation. A Ca: Mg ratio of less than unity, in particular in saline condition, adversely affects soil physico-chemical characteristics, and could decrease plant yield through nutritional imbalance. Frequent drought and groundwater over-draft have lowered groundwater level and its quality severely, including increase in salinity and, in many cases, relative increase in magnesium ion concentration. In order to assess distribution and changes in Ca:Mg ratio, laboratory analysis data of more than 6200 irrigation water samples were collected from 11 provinces. Data analysis revealed that Ca:Mg ratio was less than unity in about 55% of the samples. It was also found that increase in salinity had a significant correlation with Ca and Mg ions concentrations, but had no relation with their ratio. Correlation analysis indicated that maximum correlation was between Na ion concentration and salinity (R2= 0.86), and 60% of Ca and Mg variation could be explained with variation in salinity. However, no significant relation was found between salinity and Ca:Mg ratio. Using such irrigation water gradually increases exchangeable Mg ion and decreases soil quality (degradation of soil structure and lowering infiltration rate), and causes plant nutritional disorder. Consequently, more detailed assessment of these waters and their effects on soil and plant is enormously important from both economic and environmental points of view.
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