Healthy Soils Are: High in organic matter
Behold the benefits of organic matter!
Organic matter matters. In fact, there may be no other component that’s more important to a healthy soil than organic matter. The tiny fraction of soil composed of anything and everything that once lived—organic matter—is more than an indicator of healthy soils.
The carbon in organic matter is the main source of energy for the all-important soil microbes and is also the key for making nutrients available to plants. Here are just some of positive influences high levels of organic matter have on healthy soils:
Provides a carbon and energy source for soil microbes
Stabilizes and holds soil particles together
Supplies, stores, and retains such nutrients as nitrogen, phosphorus and sulfur
Improves the soil’s ability to store and move air and water
Contributes to lower soil bulk density and less compaction
Makes soil more friable, less sticky, and easier to work
Retains carbon from the atmosphere and other sources
Reduces the negative environmental effects of pesticides, heavy metals and other pollutants
Improves soil tilth in surface horizons
Increases water infiltration rates
Reduces water runoff
Encourages plant root development and penetration
Reduces soil erosion
Increasing organic matter: A matter of good soil health management
Considering the long list of benefits organic matter has on soil health and crop production, increasing organic matter may well be the most important management step a producer can take to improve a farm’s profitability and sustainability. In general, there are three ways to do that:
Increase the amount of plant and root production
Apply carbon-rich materials to the soil; and
Use practices that slow rather than speed decomposition.
Cover crops, green manure crops, and perennial forage crops add organic matter, as do compost and manure. Growing crops and roots add biomass above and below the soil surface. However, not all that biomass is converted to soil organic matter—much of it is released as carbon dioxide and water. It can take 20,000 pounds of organic inputs such as crop residue to increase the actual soil organic matter from 4 percent to 5 percent.
Compost in particular breaks down more slowly and improves soil structure more quickly than other organic materials. Manure breaks down quickly to add nutrients for crops, but takes longer to improve the soil than compost.
Organic Matter: Choose it. Don’t lose it.
Organic matter is vital to healthy soils, yet most modern agricultural operations are not managed in ways to retain high levels. Only half the original organic matter remains in most modern cultivated soils. In general, organic matter levels have fallen from 5-6 percent of the soil to less than 3 percent on most cropland soils.
Using tillage depletes organic matter. Each time the soil is tilled, oxygen is stirred into it, stimulating microbial action to decompose organic matter at an accelerated rate. As a matter of fact, when a woodland is cleared and planted or a prairie is plowed, most of the organic matter that was built over hundreds of years is lost within 10 years of tillage.
Combining frequent tillage with farming practices that leave little plant residue for soil microbes to eat (such as burning or removing crop residues) will lead to the depletion of organic matter.
Active and inactive, Organic Matter delivers
Organic matter can be divided into two categories: active and stabilized. The portion made of fresh organic material and living organisms, as well as partially decomposed material that is slowly decomposing, is called “active organic matter.”
Active organic matter and the microbes that feed on it are central to nutrient cycles in the soil. Nutrients, especially nitrogen, phosphorus, and sulfur, are held in this active organic matter until soil organisms release them for plant use.
This accounts for there being much more nutrient volume in the soil than is available for plant use at any one time. For example, a soil with 3 percent organic matter contains about 3,000 pounds per acre of nitrogen, but only a small part of that (30-100 pounds) may become available to plants in any one year, depending on decomposition rates.
While active organic matter may decompose over a few decades, the stabilized portion of organic matter is made of larger, more complex compounds that are much more difficult for microbes to degrade. Much of the stabilized organic matter in the soil is highly decomposed plant and animal tissues that grew more than a century, and possibly several centuries, ago. This organic matter becomes carbon-rich humus that’s resistant to further decay.
“Stabilized organic matter” or humus, acts like a sponge and can absorb six times its weight in water. It’s also a reservoir for nutrient storage, sequestering carbon from the atmosphere and other sources
Healthy soils need both active and stabilized organic matter to function well. To learn more about soil health, and to meet some of the farmers who are “Unlocking the Secrets in the Soil,” visit www.nrcs.usda.gov.