Cover Crop Termination And Preparation For Planting

Cover cropping is a popular agricultural topic primarily driven by the goal of improving soil health and water quality. Cover crops produce vegetation that can help protect the soil from erosion, improve soil organic matter and provide other benefits during the winter. However, abundant vegetation produced by cover crops can physically impede mechanical operations, such as planting, and may also introduce issues with crop production by immobilizing nitrogen in the soil, and promoting various insect, disease and weed issues which threaten subsequent crops and limit productivity.

Winter cover crops naturally grow past optimal spring planting times for primary crops, so terminating them prior to crop planting could potentially address many issues causing interference. However, the extent of the potential benefits associated with cover cropping, such as biomass contribution and nitrogen fixation, will likely be meager if they are terminated too soon. Conversely, profuse cover crop growth greatly increases many problems documented to increase failure.

Corn is the first crop suitable for planting in the spring, which stresses the timing conflict with cover crops.  Furthermore, corn is also extremely sensitive to emergence failure and plant growth disparity, compared to other primary crops, including soybean and cotton. Cover crop vegetation can aggravate these issues. Therefore, integration of these cropping systems presents considerable challenge. We have conducted research evaluating methods to incorporate cover crops into successful corn production systems.

Cover crop termination timing was a crucial management factor affecting the successful integration of cover crops with corn. Cover crop vegetation and decaying plant residue not only hindered planter efficiency and stand establishment, but also stunted corn growth and reduced grain yield if cover crop termination timing was delayed close to planting. This was caused by vegetation reducing absorption of solar radiation and limiting soil temperature, which substantially retarded corn seedling growth and resulting development.

Field Studies

Herbicide termination treatments were evaluated at two-week intervals from six weeks preplant until corn planting. A standard cover crop mixture consisting of cereal rye and berseem clover reduced corn grain yield 8% to 15% (14 to 23 bushels per acre) when terminated two to zero weeks preplant, compared with no cover crop in a traditional stale seedbed system. The cover crop produced similar corn yield as no cover crop when terminated four or six weeks preplant. Accordingly, we recommend cover crops be terminated at least four weeks prior to planting corn. The research showed corn yield reduction was greater and occurred further preplant for cereal rye, compared to berseem clover. This shows more interference was associated with cereal rye and is likely related to cereal vegetation having high carbon content, which is slow to decompose and thus produce complications, compared to legumes.

Another method to limit interference is to manipulate distribution of cover crops relative to the row where corn is planted. Our research evaluated numerous seeding methods which limited cover crop establishment in the intended planting zone or row. This included mechanical tillage treatments which concentrated seed in the furrow, rather than the row, as well as strip tillage conducted after cover crop establishment, which physically removed cover crop plants within the row. Our results showed cover crop distribution managed by various methods did not affect corn productivity when cover crops were terminated with herbicides several weeks prior to planting.

Ways To Reduce Interference

The best method to address most of the primary issues associated with growing cover crops is to terminate them prior to planting the primary crop. More time reduces the opportunity for problems to be transferred to the subsequent crop, as documented as a “green bridge” phenomenon. Problems are also strongly related to the amount of vegetation generated. Regardless, cover crops will produce vegetation or residue, which can physically obstruct seed placement, soil coverage and water imbibition, which hamper stand development.

Row-crop planters are ultimately designed to function in bare soil. Thus, substantial planter modifications are usually needed to help removing either live or dead cover crop plants anchored by their root system, which presents a significant challenge. There are a host of attachments that can be added to or replace parts on a planter including coulters, row cleaners and closing systems designed to improve planter performance in cover crops or any high residue situation. The underlining principle of these products is the ability to efficiently cut and remove vegetation from a strip where seed can be planted. Accordingly, row cleaners and closing systems generally rely on sharpened wheels with deeply serrated angled teeth to cut vegetation, remove it from the planting zone and close the seed furrow to obtain optimal seed-to-soil contact. Popular row cleaners relying on spikes or fingers are not intended to cut or remove vegetation anchored in the soil and thus, will likely struggle when used in cover crops. CS

This is a portion of an article by Erick Larson, Mississippi State University Extension specialist for grain crops. Read the full article at www.mississippi-

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