Organic matter key to soil health
The most productive soils overwhelmingly have features in common; certain physical, chemical and biological properties that allow them to function well and produce abundant biomass.
All of those features are necessary for good soil health and if even one is missing, it can affect the ability of the soil to sustain the plant growth that produces that biomass, DeAnn Presley, Kansas State University Extension soil scientist, told the South Central Kansas Residue Alliance at a recent cover-crop workshop in Norwich.
Organic matter in soil holds the key to soil health and productivity, fertility and nutrient cycling, water storage and infiltration and erosion prevention, Presley said.
She said a study of the native prairie provides a good indication of what it takes to produce abundant organic matter in the soil. The native prairie has about 6% organic matter, created over several thousand years of diverse plant growth. In the native prairie, the roots of grasses are deep and 70% of the biomass is below the ground.
• South Central Kansas Residue Alliance members learn about cover crops.
• No-till practices make for healthier soils, soil scientist says.
• Cover crops can help add nutrients and suppress weeds.
When soil is tilled, it loses carbon and nitrogen. By the 1950s, with constant-tillage farming practices, the soils near Manhattan had lost more half their carbon. In Garden City, 53% of the carbon and nitrogen were gone. No-till farming practices have started to restore the health of the soil.
Soil with residue left as organic matter becomes healthier and provides an environment in which soil organisms from bacteria and fungi to earthworms can live and function, Presley said. A single pinch of soil has up to a billion bacteria, a million fungi, up to a million algae and cyanobacteria, and as many as 100,000 protozoa.
Because of the activity of the organisms in the soil, nitrogen is broken down into a form that can be taken up by the roots of plants. They convert the nitrogen in the air into nitrites and nitrate that nourish plant life.
“You can tell how healthy your soil is by counting the earthworms,” Presley told the group. “If you shovel up a shovelful of soil and you find no earthworms, you can be pretty sure that soil is dead. And you can measure the return to health by the return of the earthworms. If you can count more than 10 earthworms in a cubic foot of soil, it is very healthy.”
Tillage kills about 25% of the earthworm population. Triazine herbicides are slightly toxic to earthworms, while many fungicides and nematicides are toxic. Regular use of ammonium sulfate, anhydrous ammonia and sulfate-coated urea has also been shown to decrease earthworm populations.
No-till helps provide the organic matter diet that earthworms live on, and their burrows form conduits belowground that improve the movement of water from the surface to the subsurface of the ground.
Along with no-till, the use of cover crops to provide an environment for soil life makes soils healthier and more productive, Presley said.
Legumes such as clovers, cowpeas, hairy vetch, soybeans, sunhemp and lupin help fix nitrogen in the soil. Wheat, cereal rye, triticale, oats, millet and barley can be used as cover crops that have the advantage of also being harvested for grain or providing forage for livestock.
Ryegrass, rapeseed, radishes and turnips have the advantage of providing biomass, soil tilth and weed suppression.
Presley told the farmers at the workshop that K-State has research projects under way at Garden City and at Ashland Bottoms. This fall, experiments will be conducted in co-planting wheat and tillage radishes with two plots in Barber County and two in Harper County. Plans are also be made to conduct similar projects in Pratt, Reno, Riley and Russell counties.
This article published in the April, 2012 edition of KANSAS FARMER.