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| thanks to everyone who has contributed to this thread.
At its peak, CRP had ~37 million acres and declined to around 20 million acres (2020) before rebounding to ~25 million acres currently.
The USDA estimates that roughly 80% of land exiting CRP returns to crop production... so its likely that 10-15 million acres of current cropland once was CRP.
While CRP vegetation varies a lot (e.g., nearly all grasses vs diverse pollinator mixes vs lots of trees), most studies of the impact of CRP on soil show significant increases in SOM after 10+ years of CRP... my quick search of the literature this weekend found fewer studies with declines in soil test nutrient levels during CRP BUT many studies either didn't measure or report changes in soil test nutrient levels.
Standard soil tests for nutrients mostly measure easily dissolved *inorganic* forms of nutrients SO organic forms of nutrients and less soluble inorganic compounds that accumulated during CRP mostly have not been measured.
Thinking about the focus of the original thread, "where are the available nutrients?", my guess is that more than half of the acres of CRP converted to cropland had intensive disturbance (e.g., intensive tillage, high chemical inputs, sometimes fire...) and most of the changes in SOM, structure, biology such as mycorrhizal fungi and immobilized nutrients that occurred during CRP were dissipated in 5 years.
I am curious about CRP conversions that resulted in both short and LONG-term benefits to crops and soils.
My intent in using the term "priming the pump" in this thread was to describe nutrient programs (fertilizer and/or manure) LOWER than recommended based on low soil tests, but produced HIGH yields.
Many of you have observed areas in fields that crank out the highest yields despite having the lowest soil test levels. The simplest explanation is that these areas are where roots grow deeper and healthier allowing more uptake of whatever resources limit yields in other parts of the field... and have lower nutrient levels in the top 6" because of higher nutrient removal by high yields.
In many cases the highest yield areas are naturally occurring rather than the result of management BUT I expect that CRP and some other soil building practices can create or expand exceptional yield zones.
With 10+ million acres of CRP now cropland, MANY of you have experience with growing crops on former CRP. Most of these fields are HEL or were lower yielding prior to CRP for other reasons.
If former CRP land has been yielding well for you, is it mostly the result of more stress tolerant genetics? or something else?
Joel
WIU Agriculture
Edited by jbgruver 1/25/2026 16:16
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Priming the pump when converting CRP to crops
