MORE importantly...NPK is water soulble...

So it washes away to pollute the groundwater.

Besides adding in the Carbon and other minerals from Compost - the carbon locks up the minerals in the soil to keep them from leeching away so fast {this is how charcoal works as a water filter}.

In fact plants don't take in all their nutrients from the roots alone - the fallacy of "acid-loving" plants. But from a soil chemists POV if the plant received ALL its nutrients thru roots the mineral balance it wants is an acidic pH, however these very plants get most nutrients thru their leaves {Usually ovoid and large} by gaseous transpiration thus will grow in normal soil with foliar feeding.

Realaize Justus von Liebig retracted his statements in later years - but by that time the modern Industial Chemical fertilizer and explosives industries were making waY TOO much money to stop the process. Tweet