Humus: The Building Block of Soil
As an industry, when we think about soil, do we ponder how we are growing or building more soil humus? What is the humus in the soil? Some call it the humusphere or rhizosphere, or more often, the active topsoil. Humus is the actively cycling carbon in the topsoil. With all the discussion of carbon fixing and carbon programs, that isn't good enough to describe building soil.
Better described as valuable compost, living soil biota, liquid manure or other organic substances gives a sense of the living aspect to humus. Beneath our feet, there are millions of microbes eating and digesting minerals as well as other microbes. It is a very complex colony of organisms. Twenty thousand species have been described, and five hundred thousand are thought to exist, all within the top twelve inches of soil. Note this does not refer at all to NPK fertilizers or salt ions. All that biomass is cycling nutrients to feed the plants growing in that soil. If we just look at a portion of this in the root hairs, it is astounding how much material is beneath your feet. This quote sums it up well:
"One small calculation is sufficient to get an idea of the significance of plant roots in the soil: The formulation of root hairs greatly increases the root's surface area. Rye (Secale cereale) has about 13,000,000 roots with a surface area of 235 square meters, and 14,000,000,000 root hairs with a surface area of 400 square meters in 1/22 of a cubic meter of soil (...) The surface area of the underground portions is thus 130 times as large as that of the above-ground portions." (Jurzitza 1987, 28)
Since that is just the root mass of a plant, we have to discuss the microbes. All those microbes such as bacteria, fungi, protozoa, etc., could be called the plankton of the soil. These organisms are the livestock in the soil that form a food chain and cycle nutrients by dissolving rock particles and eating each other to make nutrients available in many forms for the other microbes, and ultimately the plants living in that soil.
Humus formation is a type of "organic predigestion" for plants, and soil containing humus is a pantry of living nutrients during the growing season, allowing them to grow when sufficient water, sunlight, and warmth are present.
Most North American cropland is 1-1.5% (40,000-60,000 lbs per acre) organic matter, and an ideal minimum level is 4% (160,000 lbs per acre). That increase is a humus content increase. We have the tools to do this with the Growers Program. The key points to that are using that high calcium lime to open up the soil, and minimizing the salt fertilizers that snuff out humus production. Also, the high quality of Growers fertilizer does well to feed the biology cycle of that humus. I have spent the last ten years dealing with all types of fertilizers, and quality is the key to allowing biology to grow. Growers does this well.
Good luck this year!
This is an excerpt from the Early Spring Growers Solution (2025) written by James Schiltz, Technical Agronomist.
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