Why are soil containing humus fertile?

Generally, with higher levels of humus in the soil it takes less nutrients to produce a pound of produce. In other Words, the system becomes more efficient. I have recently checked 350 soil samples that I received and many of the first and second year clients have very low humus readings. The scale used by the Lamotte test runs from 1-5 with 5 being the highest humus reading.

Humus is produced in the soil by the proper decay of animal and plant matter. The principle component of humus is carbon. The color ranges from a light brown to a dark brownish-black. In order to build humus levels in soil the proper ratio of water, air, residue, bacteria, protozoa, algae, yeasts and fungi are needed. Use of acid and salt based fertilizers in excess of the soil's ability to neutralize them results in lowering, rather than building, the amount of humus in the soil.