No-till and Cover Crops for Organic Vegetable Production

Today is the 3rd update of 5 from the Great Plains Growers Conference.  Today we will look at cover crops.

No-till and Cover Crops for Organic Vegetable Production presented by Kathleen Delate, Organic State Specialist, Iowa State University.

The process of cover cropping is used to organically maintain and improve soil quality. Cover crops do this by replenishing nitrogen (legumes), replenishing carbon (grasses), decreasing erosion, managing weeds, and decreasing soil compaction. Some cover crops can even be profitable as a seed crop (if this is of interest, Dr. Delate recommends reading Managing Cover Crop Profitability). The type of cash crops will determine the ideal type of cover crop. For example, a nitrogen rich legume should follow a tomato crop and grass cover crops (i.e. rye) should never be followed by another grain (i.e. corn or wheat).

There are two different options when seeding for cover crops: over-seeding and post-harvest seeding. Over-seeding is the process of sowing the cover crop seed while existing crops are still in the field and producing. This method offers the benefit of starting the cover crop early enough to ensure that it will be healthy and vigorous. Additionally, the harvest of the existing crop is not cut short. However, the cover crop will compete with the existing crop for water and nutrients, thus potentially decreasing the quality of both the cover crop and the existing crop. If this method is selected, a shade tolerant cover crop variety must be selected, as the existing crop will already be tall and established. Post-harvest seeding is the process of sowing the cover crop seed after the previous crop has been harvested and removed from the field. With this method, there is no water, nutrient, or light competition between the new seed and the previous crop. However, the cover crop seed must be planted early enough that it can germinate and begin growth prior to prohibitive winter conditions. Thus, a grower may have to remove the previous crop before they’ve finished harvesting for the season.

Many cover crops will be in the ground over winter. At the end of the winter the cover crop will need to be properly killed in order to decrease volunteer plants throughout the growing season. Prof. Delate does mention that incorporating (i.e. tilling) the cover crop will generate the most nitrogen in the soil. If this process is chosen, it is important to chop down the crop and let that plant residue dry in the field for a few days. This ensures that the seeds of potential volunteer plants are dead. The no-till option is a process called dead mulching. This process involves using mechanical choppers or rollers to fell the crop and then leave the plant residue on the surface to serve as mulch. At this point, the cash crop can be planted. This method has the benefits of weed suppression, moisture retention, and soil conservation.

Take note of the following things when using cover crops. First, effectiveness depends heavily upon a thick and even stand of cover crops. Thin or bald patches will develop weeds, which can continue to cause problems once the cash crop is planted. Second, for optimal nitrogen benefits, legume cover crops, such as hairy vetch, should be allowed to set pods prior to killing. Lastly, cover crops should be selected based on specific soil deficiencies and specific cash crop nutrient needs. For example, a carbon rich soil should not be planted with carbon rich grasses. Planting a mixed combination of legume and grass cover crops will offer both the nitrogen and carbon benefits of cover crops.

(reported by Rachel Deffenbaugh – Gateway Greening, Inc., St. Louis, MO)