What is the story with calcium and magnesium ratios in soils?
Fertiliser recommendation systems in WA have classically used the “sufficiency” method of determining macro-nutrient cation (calcium, magnesium and potassium) requirements of crops. There is a growing controversy in WA agricultural circles on the importance of the “base saturation method” to the extent that farmers are sending soil samples out of the state and even overseas for analysis and advice. There is no dispute that base saturation and its implications for cation availability is a well established principle. However it is open to question as to whether the application of quantitative base saturation targets, established overseas on less weathered soils of higher clay content, is relevant to WA soils. In WA soils range from highly leached, cation impoverished acid sands to cation-rich alkaline mallee soils where topsoils are Ca-dominant and subsoils Mg-dominant. There is therefore good reason to anticipate that both cation deficiencies and cation imbalances will occur in WA soils
