Even well cured compost only has a few pounds of humic acid per ton which would then require 7-12 tons of compost per acre to get 35 pounds humic acid per total per acre. That amount would will provide the desired effect at the cellular level of the soil ecosystem and the cells of the crop plants. For the aging process and the formation of low molecular weight humic acids, a million years are needed for organic matter to break down to DNA and RNA fragments which are the main cytokinnins in humate. The low molecular weight fulvic acids have an auxin like effect on cells by increasing cell permeability due to the non-ionic and ionic in humic substance which enhance and stimulate nutrient flow to and between the cells. The cells can be plant, animal or microbial, but the effect is the same which is why humates are as useful as a livestock supplement as it is for growing the corn you feed them.
Biological assays are necessary to judge the effectiveness of a humate.
One big ag-chem company is now experimenting with humic acids to put in their formula because so many farmers are doing it anyway. Where phosphate availability is a problem such as on western high pH and high free lime soils, humates greatly increase phosphate availability as well as iron, zinc and manganese. This is something you need to fine-tune on your own farm by doing test plots with different amounts of fertilizer and the recommended rate of the humate you are using. The reason you can cut down is because in many cases there is more and deeper root growth and increased biological activity to release nutrients. Humates can complex nitrogen as ammonium and retain it in the root zone preventing nitification and leaching out of the root zone.