Paul Davis has done a lot of tweaking in his 20-year quest to reduce the 7-month “brown gap” many farmers see after their corn and soybean harvests are over. Keeping something green growing on his fields near West Point, Va., is the easy part.

Davis began adding cereal rye to his rotation as a cover crop after double-crop beans in 2005 to help build his soil organic matter (SOM) by sequestering carbon. His Coastal Plain soils average 1-1.5% SOM at best.

“I let the cereal rye make carbon during the months I wasn’t growing a cash crop and could take advantage of the sunlight and rain that fell on my farm during the so-called ‘brown gap,’” says Davis, who retired in 2009 after a career as Virginia Tech’s Extension ag agent for New Kent and Charles City Counties. “We’ve always had winter wheat behind our corn as part of the rotation.” 

Davis, who farms with his 94-year-old father “Boogie” Davis, says in addition to building organic matter, he was interested in scavenging nutrients left over from his summer crops and keeping them in the top soil where they could be used to offset future fertilizer costs. 

“Corn doesn’t know the difference between nitrogen that comes from cover crops and what’s purchased,” Davis says. “It just has to be there when the plant needs it.”

And that’s where Davis’s learning curve really began to climb. 

BIOMASS SAMPLES. Davis typically estimates cover crop nitrogen contributions simply by its height in late April.…