PURPOSE: To provide a fertilizer having excellent growth-promoting action of crops, soil-improving action, etc., by neutralizing the deposit of hot-spring water with a neutralizing agent to a prescribed pH and using the obtained material as a main component.

CONSTITUTION: Minerals are deposited from hot-spring gas by the ion-exchange action in the course of ascending in blue clay and are crystallized in the form of asbestos on the surface of blue clay to form natural deposit of hot-spring water. The deposit is collected and adjusted to pH5.5-7.5 or thereabout with a neutralizing agent (e. g. sodium sesquicarbonate or sodium bicarbonate) and the obtained material is used as a main component of the objective fertilizer. Since the deposit of hot-spring water is rich in nutrients necessary for the growth of vegetables, the fertilizer produced by the above process has excellent growth-promoting action of crops, soil-improving action, etc. The neutralized deposit can be used together with other fertilizer components.