Humic Acid. Humax is concentrated liquid humic acid (the “black gold of agriculture”) extracted from leonardite. The colloidal nature of humic acid allows it to absorb large quantities of water and thus increases the water holding capacity of soil. Plants grown on soils containing more humic acid tend to be more drought resistant. Humax is an all purpose soil additive used for vegetables, fruits, trees and gardens. 1 gallon concentrate makes 60 to 120 gallons solution.