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Cover Crops Go Beyond Nitrogen

Like spending money to make money, some North Dakota grain producers are using soil nutrients to grow a soil-building cover crop. They have found seeding a diverse plant community or “cocktail” as a cover crop can do much more than put nitrogen into the soil.

At a soil health workshop in Plumas sponsored by Mani toba Agr icul ture and Food, the Burleigh County Soil Conservation District (www.bcscd.com)representative Ken Miller laid out their successes with cover-crop cocktails from the last 10 years of work in the sandy loam soils around Bismarck where they average 15 inches of moisture.

Taking a holistic page from the native pasture across the fence, the Burleigh County Soil Conservation District crop farmers saw the benefits of biodiversity where warm-season grasses complement the cool-season species, both of them receiving the benefits from the neighbouring legumes.

Legumes are a large component of the “cocktail,” but the range of species stretches to do the work of improving water infiltration, adding large amounts of organic matter and retaining soil moisture. Some 33 species are on the ingredient list for the cocktails.

Diversity is best at keeping the weeds and diseases at bay in subsequent annual crops.

SEEDING POST-HARVEST

Most years they are seeded after an annual crop is harvested in late July or early August. Covering the dry soil for the winter and early spring also makes sure it doesn’t erode.

Adding fertility during the growing season, they have interseeded cow peas in a foot-tall corn crop to take advantage of the North African legume’s ability to fix over 100 pounds of nitrogen in a growing season.

The cocktail incorporates the 16-inch tap roots from radishes and turnips, which act as a drill to reach past the compaction layer nine inches down. The moisture probes have been able to find almost twice as much soil moisture post-cocktail. Other tap roots used with success have been sweet buckwheat, sunflowers and sweet clover. Those crops can also grab excess nutrients from deep in the soil profile to stop any leaching into the water table.

Most fields are zero tilled which promotes the populous crew of critters below ground that can cycle the 3,000 to 4,000 pounds per acre of organic matter into nutrients and soil tilth. About 80 per cent of the nitrogen comes from the breakdown of plant roots. As well, the corn stand didn’t require as many herbicide passes.

IMPROVED RETURNS

The cover crop segment of the field returned $49 per acre more than the conventional portion of the field. Post-cocktail, the phosphorus level was almost double the base. The nitrogen was 4.7 times higher.

Grazing critters above ground helps to expedite the return on the expenses for cover crops. They also put the standing residue down to where it has soil contact so the the micro-and macro-organisms can use it. Most of the cover crops are grazed, Bismarck farmer and conservation district supervisor Gabe Brown said in an interview. That helps provide the native range with an ample regrowth period.

Moving the soil organic matter up a few percentage points can double the water-holding capacity. Having plant residue and cover from direct sunlight can save the moisture for crop growth. Eighty-five per cent of the soil’s moisture is lost to evaporation and transpiration at a bare soil temperature of 38C. At 20C, 100 per cent is available for plants.

Different kinds of roots in the cover crops are helpful in getting the biology to work. Triticale, millet and forage barley have fibrous roots which improve top-layer soil structure and help to feed organisms working to recover nutrients.

Intercropped mixtures such as peas and annual ryegrass would be put up as silage on Brown’s operation.

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