What testing method is used to estimate soil calcium and magnesium?

The saturated paste extraction method is specifically designed to estimate the availability of soil nutrients, including calcium and magnesium, in a manner that reflects how these nutrients will behave in soil water. This technique involves saturating a soil sample with water, allowing it to extract soluble materials, and then analyzing the resulting solution for nutrient concentrations.

When soil is saturated, the ionic constituents, including calcium and magnesium, are extracted into the solution where they can be measured. This method provides a clearer understanding of how much of these essential nutrients are readily available to plants, since the saturation mimics conditions that can occur in the soil profile during periods of heavy rainfall or irrigation.

The other methods listed serve different purposes. Soil respiration tests measure microbial activity and decomposition processes; leaf tissue analysis assesses nutrient levels within plant tissues rather than in the soil; and water retention tests evaluate the soil's ability to hold moisture rather than nutrient content. Therefore, saturated paste extraction is uniquely suited for estimating soil calcium and magnesium concentrations.