Growing cover crops after small grain

By David Karki
SDSU Extension Agronomy Field Specialist

Small grain harvests in South Dakota are near completion. According to the USDA National Agricultural Statistics Service report published on August 21, winter wheat harvest has been completed, while spring wheat and oat harvest acres were 88 percent and 89 percent respectively.

Interest in using cover crops after small grain is increasing in South Dakota. Cover crops provide diversity into the cropping system, reduce soil erosion, increase soil biological activity, and also help recycle nutrients in the soil. In addition, due to diverse growing habits of major crops and selected cover crop species, it helps to break disease and weed pressure in the field. Also, cover crops can be used as supplemental fall grazing, especially in the year like 2017 where forage shortage is widespread in the state due to prolonged moisture deficit conditions.

Even though cover crops can be grown as single species or in a mixture of variety of plant species, they are mostly marketed (and grown) as blends. Selecting fall cover crop mix is critical because in a cropping sequence, it should benefit your next cash crop, not hinder with any kind of yield or growth limiting factor. Rule of thumb is that cover crops should possess growth habit that is contrasting to the following cash crop. For example, if a field is going into corn as a next crop, then higher proportion of the cover crop blend should contain cool season broadleaf species because corn is a warm season grass species. Research data from studies conducted at SDSU Southeast Research farm near Beresford have shown yield advantage in corn when grown into cool season broadleaf cover crop mix residue following small grain cash crop.

Two major categories of broadleaves commonly used as cover crop species are non-legumes (i.e. turnip, radish, canola, rape, etc.) and legumes (i.e. vetch, clovers, pea, lentil, etc.). These cool season species have high tolerance to cool temperatures and rapid fall growth; however, these species are very low in fiber content and may not accumulate abundant residue cover in the spring. In some cases, volunteer small grain growth in the fall can compensate for cool season grass species which can add to some residue next spring. Species like radish and turnip have enhanced tap roots which will aid in breaking compaction in the ground.

Legumes on the other hand will help fix atmospheric nitrogen which will contribute to the nitrogen need of other species in the mix such as radish, turnip, rate, etc. Legume species may also add to the soil nitrate content and would be readily available for next season’s crop. These species are generally winter killed.

If the crop for next year is soybean, it is suggested to put a mixture high in cool season grasses (rye, oat, barley, triticale, annual ryegrass etc.). These will produce significant amount of biomass the next spring. Winter small grain species like triticale and rye are not generally winter killed in the South Dakota environment and requires spring termination which adds extra management task in the spring.

Also, producers that are growing wheat or oat grain for seed sale, it is recommended to avoid rye and/or triticale as it may act as significant seed contaminant in subsequent years. On the contrary, winter hardy species like rye can be successfully grown in corn-soybean system and be used as prolonged cover or fall and spring forage options.