By Nick Schneider, Heidi Johnson, and Ken Schroeder
Begin with the end in mind!
This popular saying, written about extensively in Stephen R. Covey’s “The 7 Habits of Highly Effective People” is especially pertinent to a producer’s decision to grow cover crops. There are two specific questions that should be explored before planting cover crops.
Question 1: What benefit will an early season cover crop contribute to the crop rotation?
Numerous reasons are cited for growing cover crops. These reasons include: scavenging nutrients, fixing nitrogen, fighting erosion, suppressing weeds, providing forage, breaking compaction, attracting beneficial insects, and quick growth. In order for an early season cover crop to be successful, it must express two traits: cold tolerance and quick growth. Cold tolerance is necessary because an untimely frost will destroy many cover crops. Quick growth is also important because planting an early season cover crop targets a specific, narrow gap during spring.
Let us examine a few species. Buckwheat is one of the quickest growing cover crops. Buckwheat’s broad leaves and quick growth make it a favorite choice for short-term weed suppression. However, in spite of buckwheat’s ability to germinate at 45°F, it has poor frost tolerance. Poor frost tolerance makes buckwheat a risky choice as an early season cover crop.
Crimson clover and berseem clover have gained popularity as nitrogen fixing cover crops. They meet the cold tolerance criteria with minimum germination soil temperatures of 42°F, but both grow slowly, making them inferior choices as early season cover crops also.
Looking at these examples, it becomes clear that choosing an appropriate cover crop may not be easy. The Midwest Cover Crop Council has created an excellent online tool for producers to sort through numerous individual cover crops and mixtures. This tool can be found online at http://mcccdev.anr.msu.edu/VertIndex.php. Twenty to thirty species are listed for Midwestern states, including cool and warm season grasses, broadleaves, brassicas, and legumes. The tool was evaluated and vetted by university and agronomy professionals across the Midwest and Canada to ensure that it works for choosing cover crops for local soils and distinct climates. There are years of research data and grower experiences behind the recommendations.
The tool allows growers to select a state and county for regionalized results. The grower enters the cash crop that the cover crop will be planted around (before, after or interseeded), including planting and harvest dates of that crop and the soil conditions of the field, such as poorly drained or well drained. Users of this online tool have an option for selecting three goals of the cover crop that are important for narrowing down results. Examples of goals include quick growth, erosion fighter, and soil builder.
Once these criteria are selected, a table pops up that provides the different cover crops and cover crop mixtures that could meet your specifications and planting window. The user then can select from a pull down menu to see an informtion page about that particular cover crop or mixture. These information pages provide planting information, termination recommendations, potential advantages and disadvantages of the particular cover crop and more. This tool can be extremely helpful in making the best possible cover crop decisions for your farm.
Based on the criteria of early season planting (for example April 1 to May 1) and quick growth, the MCCC Decision Tool identified these species as best choices in Wisconsin: spring barley, spring wheat, oats, annual ryegrass, oilseed radish, canola/rapeseed, forage turnip, red clover, and forage/field pea. Mixtures with these species such as oilseed radish + annual ryegrass or oats are also identified as potential options for early season cover crop planting. All of the plants listed previously have a quick growth score of 3 to 5 in the attribute table. Species that were ruled out because of slow growth were hairy vetch, sweetclover and chicory.
Supplying nitrogen is often cited as a reason to plant legume cover crops. Research conducted in Wisconsin by Johnson, Colquhoun, and Bussan found that an early season pea cover crop provided only minimal nitrogen to a sweet corn crop due to the short window of time for root development and nodulation. Lack of sufficient time for growth and development would likely be an issue for other leguminous early season cover crops.
Question 2: How will the cover crop be terminated so the primary crop can be established?
This question is more difficult to answer in organic systems than conventional systems because herbicides are not an option. Many fall cover crops are killed by winter, but as discussed previously, frost is an enemy to early planted cover crops. The most likely methods for killing the early season cover crop are tillage, mowing and crimping. Crimping might have low success with the cool-season small grains because they will still be soft and pliable. Mowing will only be successful if the growing point is removed during the process. Tillage is the most likely tool for killing these cover crops. Keep in mind this rule of thumb about cover crops: if it takes many tillage passes to kill a cover crop, from a soil conservation point of view, the cover crop was not very beneficial. The Soil Conditioning Index, a model for predicting loss or gain of soil organic matter, decreases as more tillage is performed in a field.
Cover crops rightfully have grown in popularity. But there are challenges with establishing an early season cover crop prior to the primary crop. Growers need to have a clear idea of what benefit they hope to achieve with the cover crop and a timely plan for removal.
Nick Schneider is Winnebago County Agriculture Agent, Heidi Johnson is Jefferson County Agriculture Agent, and Ken Schroeder is Portage County Agriculture Agent, all at the University of Wisconsin Extension.