Building soils for better crops

Cronin Farms, Gettysburg, S.D., is making some big gains in soil organic matter. It’s risen from 2% soil organic matter to 4% organic matter in recent years — which is worth about $1,100 per acre by some estimates.

“We saw a small, slow increase in organic matter after we converted to 100% no-till 20 years ago,” says Dan Forgey, Cronin Farms agronomy manager. But the gain was limited to the top few inches of soil where crop residue was concentrated.

Key Points

South Dakota farm sees a jump in organic matter over the past six years.

The increase came by adding cover crops to the farm’s rotation.

The practice increased nutrients and soil moisture.

The latest increase — about 2 percentage points — has come over the past six years since Cronin Farms began including cover crops in the rotation after spring and winter wheat.

“We used to think you wanted to keep stubble clean after harvest to conserve moisture,” Forgey says. “But we have learned the soil likes living roots more.” He says the soil contains microbes and other organisms that thrive on live roots. “They need to be fed just like us.”

Adding cover crops after winter and spring wheat keeps a living crop on the land throughout the growing season. Cover crops haven’t hurt Cronin Farms yields, even in dry years, because the crops have increased soil organic matter.

“Organic matter acts like a sponge,” Forgey says. “It will hold up to 90% of its weight in water.”In dry years, the added capacity makes a difference in yields. “When you have reduced yields in a dry year, maybe you have to start looking at soil health,” Forgey says.

Cronin Farms has about 8,500 acres of farmland and usually plants about 700 acres of cover crops each year. Legumes add nitrogen to the soil, and grasses add organic carbon and recycle phosphorus to legume crops. Oilseed radish is planted to loosen the soil and recycle N.

“We’re still learning about cover crops,” Forgey says. “But it’s clear. They are really accelerating the increase in our soil organic matter.”

The value of organic matter

1% organic matter weighs approximately 20,000 pounds per acre. The amount and value of nutrients in organic matter is:

Nitrogen — 1,000 pounds @ 40 cents per pound = $400

Phosphorus — 100 pounds @ 40 cents per pound = $40

Potassium — 100 pounds @ 40 cents per pound = $40

Sulfur — 100 pounds per acre @ 60 cents per pound = $60

Carbon — 10,000 pounds or 5 tons per acre @ $4 per ton = $20

Total value per acre of nutrients in 1% organic matter = $560

Source: James Hoorman, Ohio State University

A big difference

No-till, cover crops, new varieties and other factors have made a big difference in Cronin Farms’ yield goals over the past 19 years. Have yours changed as much?

Yield goal Yield goal

1991 2010

Winter wheat 50 bu./a 75 bu./a

Spring wheat 40 bu./a 65 bu./a

Corn 60 bu./a 145 bu./a

Sunflowers 2,000 lbs./a 2,700 lbs./a

Organic matter 2.1% 4.0%

Fallow 25% 0%

How cover crops fit into crop rotation

Cronin Farms included cover crops in several of the 13 different crop
rotations used in 2011. The rotations were:

Forage sorghum, corn, sunflowers, spring wheat, winter wheat, cover crop, corn

Corn, soybeans, soybeans, spring wheat, winter wheat

Field peas, corn, sunflowers, spring wheat

Spring wheat, corn, field peas, cover crop, corn

Corn, soybeans, spring wheat, teff grass

Winter wheat, soybeans, soybeans, corn, oats

Winter wheat, german millet, corn, soybeans, field peas

Sunflowers, spring wheat, winter wheat, field peas, corn

Sunflowers, spring wheat, winter wheat, cover crop, corn, soybeans

Corn, sunflowers, spring wheat, winter wheat, cover crop

Corn, sunflowers, spring wheat, winter wheat, soybeans

Field peas, winter wheat, corn

Spring wheat, oats (forage), alfalfa, alfalfa

— Lon Tonneson


TAKING STOCK: Dan Forgey probes a field planted to a cover-crop cocktail. He’s seeing an improvement in soil quality.

This article published in the April, 2011 edition of DAKOTA FARMER.

All rights reserved. Copyright Farm Progress Cos. 2011.