Praveen Thakur

You can extract only water-soluble molecules. There are other molecules that do not dissolve in water and are needed by plants. For example, bone meal, phosphate rock, thermophosphates are not water-soluble...

Using water as an extractant for soil nutrient analysis is simple and environmentally friendly. Still, it often fails to adequately extract less soluble nutrients and can yield inconsistent results across different soil types. More complex chemical solutions provide a comprehensive assessment of nutrient availability, making them the preferred choice in many cases.

Plants exude various organic acids from their roots that are used to solubilize mineral nutrients from the soil matrix. Microbes exploit the root exudates while also produce siderophores and their own organic compounds that can preferentially bind nutrients, all of which form a "rhizosphere" within the soil, altering pH and nutrient availability to the benefit of the plant.

If only "water soluble" nutrients are considered, the full complexity of the soil-plant-microbe-atmosphere ecosystem is reduced to a very small subset.

Water is unable to extract all materials. It extracts only the substances and elements that dissolve in it, and not all substances dissolve in water

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