HUMIC ACID: THE SCIENCE OF HUMUS AND HOW IT BENEFITS SOIL
By Michael Martin Meléndrez
Humic acid is a group of molecules that bind to, and help plant roots receive, water and nutrients. High humic acid levels can dramatically increase yields. Humic acid deficiency can prevent farmers and gardeners from growing crops with optimum nutrition. Conventional wisdom today ignores humic acids, though, holding that it is impossible to grow and maintain an urban landscape such as a park, golf course, or lawn without high-analysis NPK fertilizers. This article will drill down into the details on humus. We can adjust our soil biology and chemistry and achieve better yields if we understand its characteristics.
HUMUS VS. ORGANIC MATTER
Adding a small amount of humus to an acre of soil can achieve positive results. Applying organic matter is certainly an excellent way to remineralize a soil that has been leached or has no chemical reactions, such as with some sands. Sand with a low cation exchange capacity (CEC) has difficulty holding onto the cations of nutrients, and these cations can easily leach deep into the soil and become unavailable for plant uptake. Sandy soils are also unable to hold onto water when arid conditions prevail and humus is lacking. Sands reside in a condition of “feast or famine,” since water and nutrients are only available for a short time after they are applied.
Humus can help retain water and the ionized nutrients that are produced by the natural cycling of organic biomass, compost, or other sources of fertilizer. The electronegativity factor of humic acids is key in developing and maintaining a healthy and sustainable soil. The source of these humic acids in a sustainable agricultural program, organic certified farm, or urban landscape can be decaying organic matter such as compost. In essence, this is fertilizer in an organic form. It is therefore important to know the ingredient source and the nutrient analysis of your compost. Humus is powerful stuff, and a tiny amount can produce a huge measurable result. We have seen as little as 40 total pounds on an acre of farmland increase the yield of a crop dramatically.
THE PHYSICS OF HUMIC ACID
Humic acids are extremely important as a medium for transporting nutrients from the soil to the plant because they can hold onto ionized nutrients, preventing them from leaching away. Humic acids are also attracted to the depletion zone of the plant root. When they arrive at the roots, they bring along water and nutrients the plant needs. long grass and soil The depletion zone is the area close to the root of a plant from which the root draws (depletes) nutrients. This zone can become particularly depleted if there is a lack of either humic acid or mycorrhizal fungus.
When plants are mycorrhizal, the depletion zone is of less importance. Mycorrhizae have hyphae micro-tubes that can extend much further into the soil than the host plant can reach. They can gather mineral nutrition for the benefit of the host plant from outside the depletion zone. Humus is even more critical for plant nutrient availability and uptake if there aren’t healthy mycorrhizal relationships in the soil. Positive ions are more easily absorbed by a plant’s root because the root has a negative charge. In other words, the positive (cation) is attracted to negative (the living root).
Humic acids hold cations (positive ions) in a way they can be more easily absorbed by a plant’s root, improving micronutrient transfer to the plant’s circulation system. This works because humic acids (ulmic, humic, and fulvic) pick up positive ions and are then attracted to the root depletion zone and to the hyphae micro-tubes of mycorrhizae. Since the root’s negative charge is greater than humic acid biomolecules’ negative charge, scientists theorize that the micronutrients are taken up by the plant’s root and are absorbed by the plant’s circulation system.
Some of the micronutrients are released from the humic acid molecule as they enter the root membrane, but we are now realizing that the plant will also uptake some of the lighter molecular-weight humic acids as well. In essence, the humic substances are chelating such cations as magnesium (Mg2+), calcium (Ca2+), and iron (Fe2+). Through chelation, humic substances increase the availability of these cations to plants.
Editor’s Note: This story was first published in the August 2009 issue of Acres U.S.A. magazine.