• By Amanda Huber, Southeast Editor •
Cover crops improve soil quality and provide benefits that help create a more sustainable production system for cash crops. Selecting a cover crop depends on the benefits the producer needs.
Audrey Gamble, Auburn University professor and Alabama Cooperative Extension soil scientist, says benefits depend on the biomass level provided by the crop. Cover crops with less biomass offer protection against erosion and nutrient loss and improved water infiltration.
“As you increase the crop biomass, you see additional benefits such as conservation of soil moisture, increased organic matter and suppression of weeds.”
More Biomass, More Benefits
Gamble says small grains, oats, wheat and cereal rye have the potential to provide higher biomass. “Small grains have fibrous root systems to scavenge for nutrients and bring those back to the surface. Increased organic matter helps improve nutrient and water-holding capacity in soils. This level of biomass improves water filtration and prevents erosion.”
Legume species such as clover and hairy vetch can fix nitrogen, some of which can be provided to the subsequent crop, Gamble says. Legumes also have enough biomass to prevent erosion and improve water filtration.
“Another species of cover crop are the Brassicas, which includes tillage radish and canola. These species have deep tap roots and helps break up soil compaction. They scavenge for nutrients deeper in the soil profile and help improve water filtration,” Gamble says.
Factors In Cover Crop Termination
Knowing when to terminate the cover crop involves many considerations as well. “When Should I Terminate My Cover Crop?” authors Kip Balkcom, USDA ARS National Soils Dynamic Laboratory; Julia Gaskin, Extension specialist, University of Georgia; and Nathan Lowder, NRCS soil health specialist, say the answer depends on when the cash crop needs to be planted.
Another consideration is how wet the soil is and whether field work can begin without creating a mess. The amount of biomass and maintaining its benefits are also important.
Maximize Biomass Levels
The authors say, “In March and April, biomass of cover crops can double in two to four weeks.”
It may be worth delaying planting to take advantage of this burst of cover crop growth, especially if the goal is to maximize weed suppression.
Research shows that 8,000 to 10,000 pounds per acre of cover crop biomass is needed for effective weed suppression.
The options for terminating are many and include roll, spray and plant in one pass; or roll and spray; roll and crimp; or only spray to terminate the cover crop. Leaving a three-to-four-week window between termination and planting provides an opportunity to recharge soil moisture while maintaining benefits.
Set Up For Planting
While planting into cover crop residue can be intimidating, it is possible to have a good stand, say Balkcom, Gaskin and Lowder in the bulletin, “How Do I Get Good Seed/Soil Contact in Cover Crop Residue?”
“Your strip-tillage rig needs a good, sharp cutting coulter ahead of the shank to slice the cover crop and prevent the residue from wrapping around the shank,” they say. “Make sure your cutting coulters stay sharp. These coulters perform best when running on firm ground; consequently, they should be mounted well in front of any sub-soiling shank.”
Another possibility is the use of row cleaners. The goal is to have the wheels of the row cleaners barely touching the soil surface to minimize disturbance while the residue is swept aside allowing the double disc openers good access to the soil.
Good Seed/Soil Contact
Make sure to use the correct down pressure. “Down pressure springs or hydraulic systems can reduce bouncing and keep the seeding depth consistent. Seed firmers are another option to ensure good seed-to-soil contact.”
Finally, the authors say producers need to select closing wheels based on soil type. For clay soils, many producers prefer spiked closing wheels to prevent soil crusting. With sandy-textured soils, rubber closing wheels firm the soil and prevent soil moisture loss.
From beginning to end, cover crops come with a list of decisions to be made regarding selection, termination and subsequent planting of the cash crop. However, the benefits they provide are worth careful consideration.