Frank J. Buchman

Cowboy • Horseman • Writer

Plant Species Differ In Benefits Of Cover Crops

“Long-term cover crop growers sometimes realize better yields of cash crops, and sometimes they find they’re able to use fewer chemical inputs,” according to Extension crops researchers.

“Because they’re keeping living roots in the soil, the channels created by the roots help with water infiltration.”

The cover crops shelter the soil surface, and this, along with some of the glue secreted by roots, helps soil resist erosion. Cover crops also help to suppress weeds and cycle nutrients in the soil.

Researchers’ trials have shown that combining cover crops with no-till creates soil health benefits exceeding those created by no-till alone.

The two practices combined with applications of manure create the greatest soil health benefits.

In an on-farm project, researchers compared a field in no-till for more than 10 years to an adjoining no-till field growing cover crops for five years. They compared both fields to an adjoining no-till field growing cover crops and receiving manure.

The straight no-till field had soil organic matter (SOM) of 3.3 percent; the no-till/cover crop field had SOM of 4.5 percent; and the no-till/cover crop field receiving manure had percent SOM.

Water-infiltration rates followed a similar trajectory. Soil in straight no-till fields infiltrated water at a rate of 1.09 inches per hour. Adding cover crops to no-till increased water infiltration to 2.51 inches per hour.

Applying manure to the no-till/cover crop fields further increased water infiltration to 3.33 inches per hour.

Urine and manure deposited by livestock grazing the cover crops similarly benefit soil health. Livestock grazing offers the added economic benefit resulting from the harvesting of livestock feed without losing benefits to soil health.

A significant percentage of the nutrients in the cover crops grazed by livestock are recycled in the soil.

Seventy to 80 percent of the nitrogen, 60 to 85 percent of phosphorus, and 90 percent of potassium is excreted in the manure.

Over time, these nutrients replace fertilizer for crops. Farmers who are most successful with cover crops are those using livestock to harvest some of the cover crops.

A complex crop production system offers prime opportunity to incorporate cover crops.

Including winter wheat in the rotation, for instance, provides a window for establishing cover crops in midsummer, after wheat harvest. This gives a greater chance for the cover crop to get established and provide fall grazing for livestock.

Cover crop species and mixes have different purposes. Some fix nitrogen in the soil. Some address issues with compaction. Some soils with low organic matter need cover crops high in carbon.

Certain mixes are best for early-season grazing, and others are best for late-season grazing.

In general, the differing plant families of cover crops each provide different services to the soil. Grasses tend to yield cover crops that are high in residue, providing shelter for the soil surface.

Legumes fix nitrogen in the soil. Brassicas counteract compaction with their roots, and their residue contributes to nutrient cycling in the soil system.

One of the most popular cover crop species is cereal rye. Rye is winter-hardy, pesticide-tolerant, and stimulates soil biology, which helps recycle nutrients and build soil structure.

Reduced seed cost is another benefit of cereal rye as a cover crop. The cost of cereal rye seed came to $10 or less per acre, while the cost of seed for mixed species cover crops averaged a little more than $20 an acre.

While cereal rye is cost-competitive to establish and offers multiple benefits to the soil system, when grown as a single-species cover crop, it usually yields less biomass than multispecies cover crops.

High amounts of biomass typically result from cover crop mixes designed to build soil carbon.

Biomass is important because, as it is recycled in the soil, it puts carbon back into the soil system.

On-farm yield comparisons of various cover crops have shown that cereal rye planted in October and November following corn and soybean harvest yielded 1.45 tons of dry matter per acre in May.

By comparison, the average yield of a five-species cover crop mix following wheat and measured in October amounted to 3.24 tons of dry matter per acre.

One multispecies high-carbon mix researchers evaluated had sorghum sudan, pearl millet, grain sorghum, spring barley, sunn hemp, okra, sunflower, flax, African cabbage, spring oats, and buckwheat.

When the goal is fixing nitrogen, researchers have found legumes provide varying amounts of nitrogen to the soil system.

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