FAYETTEVILLE, Ark. – Soil organic matter means there’s much more to dirt than meets the eye.
“Organic matter is critical for healthy soils,” said Dirk Philipp, assistant professor for the University of Arkansas System Division of Agriculture. “It’s storage of available nutrients, it bonds soil particles for stable structure and can hold water.”
Soil organic matter:
- Can hold up to 90 percent of its weight as water
- Can release 25 pounds of nitrogen and 5 pounds of potassium per acre depending on its proportion to other soil components
- Provides a water-permeable soil structure
- Prevents erosion.
How organic matter winds up in the soil depends on what’s growing. It can come from plant residue, decomposing microorganisms, cover crops, organic fertilizers such as manure or poultry litter.
Building up organics in the soil takes time and volume. Philipp said it takes about 10 pounds of organic material to produce a single pound of organic matter.
“Decomposing below-ground biomass such as roots was a major source of organic material in native grasslands, or prairies, that eventually led to the relatively high levels of soil organic matter in dominant soils of the Midwest,” he said. “In the southeastern U.S., much of the original cover was forest. With trees living much longer than grasses, that translates into a relatively low soil organic matter content.”
Building, maintaining organic matter is key
In areas of Arkansas that were forested and converted to pasture and cropland, “soil organic low to begin with, so increasing it is of paramount importance to farmers,” he said.
Measures for maintaining and increasing soil organic matter include reducing erosion by maintaining appropriate stocking rates, avoiding overgrazing, preventing bald spots in the pasture and using no-till techniques to establish crops in rotations.
Soil testing is important too, and should be done frequently to ensure nutrients are at optimal levels, Philipp said, adding that testing ensures that forage growth isn’t limited by nutrients and allows forage growth that will, in turn provide biomass growth.
“Nutrients can be added as litter in accordance with nutrient management plans,” he said and adds that producers should strive “for even distribution of animal excretions through management strategies that are adapted to the particular location.”
Other recommendations include focusing on extending the grazing season by closing gaps in forage production and recycling nutrients through appropriate stocking rates. Philipp also says that grazing removes fewer nutrients from the soil than haying.
In row crop situations, cover crops can be grazed by animals and this allows nutrients to be recycled, Philipp said.