Humic Acid: By Popular Demand

Posted by Katie Elzer-Peters
April 29th, 2009
Filed in Compost
Tags: Compost, composting

Well, most of my friends wanted to hear about something other than humic acid, so I’ll get to their questions tomorrow.

We frequently talk about compost on this blog. Compost is the “miracle pill” for the garden. An addition of compost can improve the worst soils.  Making your own compost is relatively easy and inexpensive.  However, if you can’t make your own compost, you can add an elemental form of compost to your garden, to help your existing soil improve itself!

Here’s why you’ll want to add humic acid or compost to your soil SOON if you have not already done so:
Compost:

• Improves soil structure
• Improves drainage
• Improves water holding capacity
• Adds nutrients to the soil

What is Humic Acid?

When compost is broken down into its very basic, chemical building blocks, it forms humus. Humic can be broken down into humic acid by treating the humus with sodium hydroxide and lowering the pH of the solution to 2. At that point, the organic matter will separate, and can be dried to form humate. It sounds too good to be true—the same substance that helps break up clayey soils and improve drainage and oxygen exchange also helps sandy soils retain nutrients and water. Many chemicals have been developed from the beginning of agriculture, but none can rival organic matter, especially humic acid. Humic acid improves plant growth, microbial activity in soil, plant growth and respiration, as well as other natural processes. It provides little in the way of plant nutrients, but increases the ability of the soil to hold nutrients in a way that can be easily taken up by plants. Because humic acid is in such an elemental form, it is difficult to describe it precisely, however the work that it does in the soil is vital to healthy plant growth.

How Humic Acid Benefits the Soil

Humic acid facilitates ion exchange. Humic acid has a higher cation exchange capacity, or CEC. That means it is easier for soil nutrient particles to move within the soil, and thus to be taken in by plants. Soils treated with humic acid have much better nutrient availability. Humic acid does not directly supply the plants with nutrients, but it does make what nutrients are in the soil easier for plants to access. Humic acid also influences the pH of the soil, which affects nutrient availability. Clay soils with very low humus levels can become overly acidic, resulting in poor conditions for plant growth. Sandy soils can be overly alkaline, equally as problematic for plants and nutrient uptake. Humidic acid increases the buffering capacity of the soil, and allows pH to remain steadier.

Humic Acid and Nutrient Uptake

In addition to nutrient availability, nutrient uptake is an important part of plant growth. If the nutrients are there, but the plants cannot absorb them, the nutrients do not benefit the plant growth. Research has also shown that humic acid makes the cell walls of plants more receptive to nutrients and more permeable to the nutrients. This saves gardeners money, as well as encourages healthy plant growth. If you feed the soil, but conditions in the soil prohibit plants from taking up the nutrients, your money is, literally, going down the drain. (And, into the groundwater.)

Compost and Soil Oxygen

Low amounts of oxygen and oxygen exchange in soil cause problems with plant roots. Plants are said to “eat” carbon dioxide and release oxygen. That is more or less true, to a point. Plants take in carbon dioxide to use in photosynthesis, the chemical reaction catalyzed by sunlight where plants make sugars from carbon dioxide and water. Plants also undergo respiration, which is the process of breaking down the sugars they have stored to use as building blocks for new growth. Oxygen is needed for respiration, and plants get that oxygen from the soil—taking it in through their roots. Sandy or clayey soils do not usually have a good balance of water and oxygen in the soil. Compost helps restore that balance.

Compost is the Duct Tape for Gardeners

The bane of every gardener’s existence in half of North America is clay soil. The other half struggles with sand. Soils with high clay content hold water and do not drain well, which causes root problems in plants. If the roots are in trouble, the whole plant will soon be in trouble. Sandy soil drains rapidly, giving plants little time to take in the water they need to grow. Clay particles hold tightly to nutrient particles, which makes it more difficult for plants to take up the nutrients they need from the soil. Overly sandy soils do not hold nutrient particles well at all. Compost can fix that problem. If compost is not available, you can add humic acid as a soil conditioner, which will help existing soil microorganisms do their work to improve the soil.