CRP Mid-Contract Management: When and How to Interseed

A CRP field seeded to a diverse mix often reads as solid grass by the middle of the contract. The grasses close the canopy, and the forbs, the broadleaf flowering plants that carry the wildlife value, lose the light. Interseeding is one of the fixes a conservation plan can list, and the seeding date decides whether it takes.

What is mid-contract management?

FSA writes management activities into the conservation plan so the cover keeps providing plant diversity, wildlife value, and protection of soil and water for the length of the contract [1]. Contracts run 10 to 15 years, which is a long time for a stand seeded once to thin and go flat [1].

The generic plan FSA publishes for CP-1, introduced grasses and legumes, schedules weed and invasive species control in year 3, then light disking and overseeding in years 4 and 8 [1].

The native grass version, CP-2, splits the field in half [1]. Burn or light disk half the acreage in years 3 and 7 and overseed in year 3, then treat the half left alone in years 4 and 8 and overseed again in year 4 [1].

Cost sharing may be available for required management activities listed in the plan at a rate of 50 percent [1]. No work happens during the primary nesting season of April 15 to August 15 [1].

When does the dormant seeding window open?

Dormant seeding puts seed on ground cold enough that it sits until spring instead of sprouting into a freeze. University of Minnesota Extension sets the threshold at soil temperatures below 40 degrees Fahrenheit, which in most of Minnesota runs from early November to the middle of March [2].

Air temperature is the rougher guide most landowners watch. Iowa State University Extension defines a hard freeze, or killing frost, as 28 degrees Fahrenheit or lower [3].

Its county tables track the softer 32 degree mark [4]. In Adair County, Iowa, the average first fall freeze at 32 degrees falls on October 7, and only one year in ten brings it before September 26 [4].

Soils across the Northern Plains cool past the dormant threshold earlier than the southern Corn Belt. A Dakota interseeding often goes in through late October, while a southern Iowa job can wait into November.

How to choose between fall dormant and spring frost seeding

Frost seeding is the late winter counterpart, with seed broadcast onto bare, frozen ground and worked in by the honeycombing that freeze and thaw cycles create at the soil surface. Iowa State University Extension puts that window between mid February and early March [6].

Two things separate the methods, and the first is the seed itself. Frost seeding is generally not recommended for grass species, and it leans on small, dense legume seed [6].

The second is soil texture. Sandy soils do not expand and contract enough to heave seed in, so loam and clay soils tend to do better [6].

Dormant fall seeding suits the northern half of the CRP map, where the cold sets in early and holds. Frost seeding fits latitudes with a real February thaw, and it can be run again the following year if the first pass does not take [5].

How to put seed into standing cover without a full reseed

Seed dropped onto undisturbed sod rarely reaches mineral soil. The disturbance FSA pairs with overseeding in its own example plans is light disking, and burning is the other listed option [1].

Pick the delivery method by what the ground looks like after that disturbance:

• A native seed drill with agitated small seed boxes, where residue is short and the openers can hold depth.
• Broadcasting onto disked strips or a fresh burn, followed by a cultipacker or by winter freeze and thaw.
• Treating part of the acreage on each pass, the half and half pattern the CP-2 example lays out [1].

Broadcast rates run above drill rates because seed placement is less precise. Both methods do better with a second pass run across the first.

Which species establish from an interseeding and which rarely do

Small, hard seeded legumes are what establishes, persists, and pays for the pass. Penn State Extension lists frost seeding rates for pasture renovation of 4 to 8 pounds per acre of red clover, 2 to 3 pounds of white or ladino clover, and 4 to 6 pounds of birdsfoot trefoil [5].

An FSA example for wildlife openings inside a CP-3 tree planting calls for light disking followed by broadcasting 5 pounds per acre of partridge pea [1]. Penn State Extension also advises inoculating legumes with the appropriate rhizobium, the soil bacteria that let the plant fix nitrogen, before the seed goes out [5].

The species that rarely come from an interseeding share one trait, which is that they need an open seedbed and a season of low competition. Fluffy native grass seed does not meter through a broadcaster, and small forbs sown into unbroken thatch tend to disappear.

Get the activity into the conservation plan first

FSA states that mid contract practices are site specific, and that the required practices and their timing are determined during conservation plan development by the landowner and the NRCS or technical service provider planner [1]. Ordering seed ahead of that conversation is how a mix ends up outside the practice it was bought for.

Two dates control the calendar, the contract year the activity is scheduled for and the nesting season closure from April 15 to August 15 [1]. A fall dormant seeding lands after that closure, and a spring frost seeding lands well before it.

Settle the practice code and the seeding date in the conservation plan first, then match the mix to what the plan names. If you are scheduling a mid contract interseeding for this fall or next spring, NativeSeed Group can build the forb and legume list against that practice: native wildflower and forb seed.

Sources

[1] USDA Farm Service Agency. General CRP Signup 43 Job Sheets. https://www.fsa.usda.gov/Internet/FSA_File/crp_su43_jobsheets.pdf

[2] University of Minnesota Extension. Dormant seeding to establish or improve your lawn. https://extension.umn.edu/lawn-care/dormant-seeding

[3] Iowa State University Extension and Outreach. Predicting the First Fall Frost and Freeze Dates. https://crops.extension.iastate.edu/blog/justin-glisan/predicting-first-fall-frost-and-freeze-dates

[4] Iowa State University Extension and Outreach. Frost and Freeze Dates in Iowa, Adair to Buchanan Counties. https://yardandgarden.extension.iastate.edu/frost-and-freeze-dates-iowa-adair-buchanan

[5] Penn State Extension. Frost Seeding for Cover Crop or Forage Establishment. https://extension.psu.edu/frost-seeding-for-cover-crop-or-forage-establishment

[6] Iowa State University Extension and Outreach. Frost Seeding Legumes. https://crops.extension.iastate.edu/encyclopedia/frosting-seeding-legumes