Agriculture Reference
In-Depth Information
Organic Matter
We have seen that while organic matter makes up a relatively small part of the soil, it is
critical. It's kind of like how you can make bread without yeast, but it won't work very
well. You just need that teaspoon of yeast in there. Organic matter is as important in the
soil as yeast is to bread. You just need perhaps 3% to get you started.
Organic matter is anything that is living or was once alive. When looking at the soil,
we're mostly referring to fallen leaves or needles and twigs, dead and live plant roots, and
dead and live microbes. All of these can be fresh and whole, or in the process of being
broken down, or already broken down into its most stable form — humus. Compost is or-
ganic matter, too.
We've seen that organic matter takes center stage when it comes to water-holding capa-
city and drainage, promotion of air in the soil and resistance to compaction, holding onto
cations and anions, and providing fertility because it is made of nutrients and other sub-
stances. It's said to be a particularly important source of nitrogen, phosphorus and sulfur,
but has many micronutrients, too. Not only is it a source of nitrogen, but nitrogen-fixing
bacteria actually need it for energy so they can do their job.
Organic matter is the source of many compounds in the soil, such as certain phenolic
acids and auxins. These enhance plant growth and help protect plants from predators. More
high-quality organic matter in the soil generally means more beneficial organisms and few-
er non-beneficial organisms.
Humus is organic matter that has been broken down so much by microbes that it resists
being broken down any further. The microbes will work away at it if there is no other food
available, but they'd prefer something else. By the time organic matter has been trans-
formed into humus, many of the elements have already been released.
In the soil, humic acids are important chelators, which means they combine minerals into
organic compounds that are more available to plants. They also tie up toxins, making them
less available to plants. Humic acids will already be present in good soils with a lot of or-
ganic matter. Otherwise, they'll be lacking and it will be beneficial to bring them in as a
supplement (called humates), while also focusing on increasing the organic matter content
of the soil.
Humic acids greatly improve the soil, increase plant root growth and metabolism, en-
hance seed germination, and help plants deal with environmental stresses. They remove
odors in slurry and compost piles, and keep irrigation lines clean. We also use humates in
liquid applications of organic fertilizers onto plant leaves, because they help the plant take
up and utilize the nutrients in the solution many times more effectively.
