America’s oldest farming operation is profiting from improved soil quality and no-till cropping on mined land.

The Shirley Foundation traces its roots back to 1613 as the oldest continuous farming operation in North America. Charles Carter, the 11th generation of the family, says it has turned into an extremely diversified, highly innovative no-till operation.

Tobacco was the big crop until the early 1800s and even then the Charles City, Va., family recognized the value of conservation practices and crop rotations in protecting the land. Much of the ground is no-tilled today to improve soil quality and boost crop profits.

Reclaiming Mined Land

In the 1990s, the plantation owners wondered if there was a way to return land disturbed by sand and gravel mining done by the previous generation to prime farmland.

Further discussions led to a research partnership between the plantation owners and Virginia Tech soil researchers to evaluate the impact of deep tillage and biosolids application on mined ground.

Then, 10 years ago, the land reclamation project took on a more dramatic look. This was due to a unique opportunity that came out of a bridge building and dredging project in Washington, D.C.

When construction of the replacement Woodrow Wilson Bridge that connects Virginia with the nation’s capitol meant the Potomac River in that area needed to be deepened, Carter learned the contractors had to find a home for 502,000 cubic yards of freshwater dredged soil material.

BONUS SOIL. Over 500,000 cubic yards of dredged material from the Potomac River in Washington, D.C., were barged 240 miles south to help reclaim sand pit ground.

Securing soil samples for testing, Carter and Virginia Tech researchers determined the dredged material that was to come from the Potomac River contained 35% to 45% silt, had a pH of 7 and was comparable to some of the best soils in the nation. Analysis indicated the dried dredge material was a silt loam soil that was low in both metals and organics.

Lee Daniels, a Virginia Tech soil scientist, says the chemical and physical properties of the dredged materials turned out to be equal to or superior to the best topsoils in the state’s southeast region.

Barging The Soil

Carter had previously formed Weanack Land Limited Partners with the goal of reclaiming, restoring and repurposing beneficial reuses of the plantation’s low-value mined land.

Research help came from scientists at Virginia Tech, Old Dominion University and Potomac Crossing Consultants.

The dredged material was barged 240 miles down the Potomac River, through the Chesapeake Bay and up the James River to the plantation.

Rather than buying this valuable product, Carter was paid a significant amount to cover costs of permitting, monitoring, dike construction, soil conversion, vegetative establishment and reclamation costs.

NEW TOPSOIL FORMED. Truckloads of the dredged material were spread to a depth of 7 feet and mixed with composted wood fines on compacted sand pit ground.

“We won’t handle material that doesn’t meet environmental standards — all material must meet regulatory sediment screening levels,” says Carter.

Much of the dredged material arrived at the plantation in late 2000 and was spread to an average depth of 7 feet over 40 acres of compacted ground that used to be an old sand mining pit.

“The remaining compacted clays left behind by mining make for lower-quality soil,” Carter says. “We prefer to place enough material over the clay to reach a minimum of a 3-foot depth for the rooting zone, along with some extra material to allow for smoothing out the uneven bottoms of mining pits.”

By the summer of 2001, the dredged material had dried out enough to start developing a farming program.

In mid-August, a rotary cutter was used to knock down the existing vegetation and scrub forest seedlings. This was followed with discing and rototilling to break up clogs and cracks caused by the dry down of the dredged material and to incorporate fertilizer.

Winter wheat was seeded as a cash crop on some of the ground and as a cover crop in areas to be planted to corn the following spring.

In mid-April, composted wood fines were mixed into the cured dredged soil at rates ranging from 0 to 150 dry tons per acre. This area was disced to incorporate the compost, herbicides and fertilizer prior to planting corn.

Amazing Results

Corn yields were outstanding, going as high as 230 bushels per acre in some areas, says Daniels. The composted wood fines dramatically reduced the need for nitrogen in obtaining high corn yields.

AMAZING RESULTS. Following a wheat cover crop, corn yields were as high as 230 bushels per acre only 2 years after the dredged material was spread.

Wheat yielded as much as 36 bushels per acre that first year, but was limited by lodging and an amazing amount of animal damage.

“We’re convinced these newly deposited dredge soils may be as productive as natural soils in the region,” Daniels says. “From a narrow standpoint of bulk-soil chemical properties and fertility, these newly developed soils are outstanding and are actually superior to most native agricultural soils.

“The pH of the surface soil ranges from 6.8 to 7.4, despite several years of oxidation and weathering.”

Shallow- and deep-well monitoring indicated there were no water or nutrient concerns on the reclaimed land.

New Jersey Project

Between 2005 and 2007, Carter barged 300,000 cubic yards of dredge material from the Earle Naval Weapons Station pier replacement project near Sandy Hook, N.J., to the Virginia plantation.

Since it typically takes a couple of years for the sediment to dry and cure into a farm soil, these fields were seeded to winter wheat last fall.

“We missed the second nitrogen and some pesticide applications after very heavy rains last spring,” Carter says. “The fine-grained sediment may need another year of seasoning for full agricultural productivity.”

Soil Productivity

Carter is impressed that the cation exchange capacity was over 30 for the Earle material, even if the CEC is affected by salinity and will drop a bit over time due to the influence of salt.

“It was 15 for the Woodrow Wilson Bridge project’s 502,000 cubic yards and that’s turned out to be some of the best farm soil we have,” he says. “Our best native farm soil is the Pamunkey series that typically has a CEC of 12 to 13, so the soil productivity with these dredged materials is much higher.”

Daniels says this is a high-quality soil.

“It requires no lime, as it’s base-saturated with 4% calcium mostly in the form of shells and calcite, needs very little fertilizer and has had a higher germination rate than seed on our best native soils,” he says.

Opportunities For Others

River-channel and harbor-dredging activities in many areas of North America generate hundreds of millions of cubic yards of dredge sediments annually.

Up until now, there’s been little beneficial usage for these dredged materials. But this could change for innovative no-tillers willing to invest in new ways of improving soil quality and actually creating new amounts of topsoil.