Why do the guide levels for calcium, magnesium, potassium and sodium change on each soil report, even if I am growing the same crop?

The optimum guides for calcium, magnesium, potassium and sodium change depending on the cation exchange capacity (CEC) - as we use a soil balancing approach to soil fertility management, we want to see balanced calcium/potassium/magnesium/sodium % levels on soil colloid (look at the bottom box on the soil report called "Percentages & Ratios"" to see how well balanced your soil is.

Therefore to balance a heavy clay soil with higher CEC will require higher levels of Ca/K/Mg/Na, therefore the target guides will be higher than a sandy soil with lower CEC where less nutrients will be needed to balance the soils - this is why guides changes, its based on cation exchange, which is determined by clay content and clay type.

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