The Importance of Organic Matter in Healthy Soil

Soil is, literally and figuratively, the beginning of great gardening. Plants take in much of what they need, in terms of oxygen, minerals, water and food, from the soil. Open any horticultural or agricultural textbook, and you will see advice along the lines of "if a plant is having problems, check the soil and roots first." If a tree is ailing, the first place to look is not the leaves, but around the trunk, and the soil. (The main reason to look at the trunk at all is to see if transportation of water and food from the roots to the top of the tree has been disrupted by a girdling of the tree.) For gardeners interested in keeping an organic garden, rich, nutrient-dense soil with high organic matter content is a must. Without good soil, gardeners will spend a lot of time trying to fix problems above-ground, which would not be a problem if the soil was healthier.

What is Organic Matter?

To understand why organic matter is so important for soil, first you need to understand what it is. Chemically speaking, the term "organic" refers to molecules with carbon in them. The benefit of organic matter does happen down at the smallest level-atom exchange. Humus is organic matter that has been completely broken down and can exchange nutrient molecules. Shredded leaves, mulch, and grass clippings are examples of organic matter that has not been broken down. Fully "digested," "composted," or "broken down" materials are in a form that can be transported through the soil to plants. It is more accurate to use the term "transported" than "eaten" or "consumed." The movement of molecules from the soil and the plant cell wall is a chemical reaction based on charges (positive or negative) of the molecules and the plant cell. Without going into really boring botany-class mode, it is pretty interesting how plant roots work at the cellular level to take in water, oxygen, nutrients and minerals that plants need.

Organic Matter is not just good for Plants

Organic matter is necessary for plants to have the nutrients they need-it is from organic matter that plants get their nutrients. Organic matter does so much more, though. It provides food for micro-organisms and macro organisms that live symbiotically with plants. Those organisms break down larger bits of organic matter into molecules small enough for plants to take in. Organic matter improves soil structure. The myth that healthy soil is completely uniform in consistency is just that-a myth. Water and oxygen fills the spaces between soil particles. If the soil is ground to a very fine dust, it is prone to erosion problems, in addition to problems with drainage and oxygenation. Organic matter helps regulate temperature. It also holds water and improves drainage at the same time-something that is almost impossible to replicate with any synthetically produced material.

Ways to add Organic Matter to the Soil

Organic matter does affect soil differently depending upon the state of decomposition of the compost. Fresh organic matter will be decomposed by soil organisms. During that process, nitrogen can be tied up. If you apply un-composted organic matter to the soil, you may need to add nitrogen. A good organic form of nitrogen is humic acid. Because the organisms that break down organic matter work based on the temperature of the soil, compost breaks down faster during warm weather and slower during cold weather. (This is different than hot and cold composting.) Because of that, you can spread a layer of shredded leaves or organic mulch in the fall, and it will slowly decompose during the winter. During the spring you can turn over the soil and add the broken down organic matter into the soil. The deeper into the soil the organic matter goes, the more water-holding capacity and drought resistance the soil will have. There is one instance in which you should not add organic matter into the soil. If you are planting a new tree, you should not add the compost into the hole, as that has been scientifically determined to discourage root growth beyond the original planting hole. It is better to top-dress the tree planting, using compost as a kind of mulch, rather than a soil amendment. Additionally, never till in the compost-that essentially defeats the purpose of improving the soil structure. Organisms in the soil will digest the organic matter and disperse it throughout the soil naturally.

Casey Coke is a Marketing Manager for Natural Environmental Systems, LLC, a global supplier of soil amendments and humic acid products.