Sodium, calcium and magnesium ratios in soils of NW Victoria, Australia may restrict root growth and crop production

Fifty-six sites throughout the Wimmera region of Victoria were sampled to 1 m depth, and 1: 5 extracts analysed for pH, conductivity and cation content. The relationship between conductivity measured in saturated extracts and 1: 5 extracts at five sites was used to calculate cation concentrations expected if saturated extracts had been prepared. Soils were generally alkaline and cations at depth were dominated by sodium. The ratio of sodium to calcium varied from <2.6 (10% of samples) to >85.5 (10%) to a maximum of 247.1. It exceeded 12.8 in 40% of samples, and exceeded 45.6 in 20% of samples, levels which are likely to reduce root growth and ability of roots to exclude sodium. Higher ratios were associated with depth, pH and conductivity. The ratio of magnesium to calcium exceeded 1 in 80% of samples, 2 in 55% of samples, 3 in 30% of samples and the maximum measured was a ratio of 7.6, suggesting plant growth may be reduced. The issues of extrapolating from experiments in solution culture to soil, and errors likely in using 1: 5 extracts are discussed.