ON-FARM THOUGHTS: Managing Unseeded Acres with Annual Cover Crops
by John McGregor, MFGA Extension Support
The end-of-June 2022 Manitoba Agriculture Crop Report stated more than 150,000 acres were planted after the June 20th final crop insurance seeding deadline. Additionally, the report estimated there were over 880,000 acres still unplanted due to excess moisture and that there still remains nearly 700,000 unseeded acres across Manitoba.
If farmers have land that was too wet to seed this spring, planning to manage those unseeded acres can help save nutrients, control weeds, improve soil health and even provide some cash flow. Planting a cover crop to these areas can help control weeds and prevent erosion, while enhancing soil structure and preventing “fallow syndrome”.
Note: Fallow syndrome can occur when there is not enough living root material for beneficial soil mycorrhizal fungi to survive as they require actively growing roots to survive. These “good fungi”, also known as AM (Active Arbuscular Mycorrhizae) fungi, facilitate the uptake of nutrients that are less mobile in the soil, such as phosphorus (P) and zinc (Zn). Fallow syndrome has the potential to severely limit crop growth and hurt crop yield the following year if no crop or weed growth has occurred in the previous year.
If you have some unseeded acres this year and you are considering a cover crop for any of the above reasons there are a few points you should consider:
· Check which residual herbicides might be in your soil to give cover crops best chance of success.
· Think ahead to spring 2023. Cover crops that winterkill, such as oats, radish, turnip, barley, and some clovers, eliminate the need to plan a spring termination. Cover crops such as fall rye, winter wheat or sweet clover will overwinter. If you’re interested in a cover crop which overwinters, make a plan for termination that fits with your rotation and herbicide program.
· Select a cover crop to provide coverage throughout the rest of the 2022 growing season. Cost, availability of seed, and when you can plant are key factors when deciding what cover crops to plant and if it should be a single species or a mixture of cover crops.
· Seed a cover as early as possible to compete with weeds. Remember spring cereals such as oat, barley and spring wheat may develop a seed head, which could shatter and produce volunteer plants. Brassicas (e.g. radish, turnip, and canola) can help break up compaction with their taproots, but some species may bolt and produce seed if planted too early.
· If it gets late, adapt. Control weeds with an herbicide or tillage before planting a cover crop. If you use an herbicide, keep in mind the potential for herbicides to impact cover crop establishment.
· Use a reliable seed source. Use good quality seed that has been cleaned, tested for germination and weed seed contamination.
When looking at covering unseeded acres using a cover crop, usage usually falls into two areas, green manure or green feed.
Green manure:
Fields that were flooded or saturated for significant periods of time this spring could be subject to leaching or denitrification and may have compromised nitrogen fertility. Green manure crops can help salvage or rebuild nitrogen fertility while also drying out the land. At the same time, green manure crops add organic matter to soil, and improve soil structure and drainage.
Green feed:
Seeding annual crops such as barley or oats for green feed or swath grazing can provide high-energy feed for livestock in a short period of time. Barley and oats also can be used as summer pasture within four to six weeks of seeding.
If the main objective is moisture removal, harvesting the crop as green feed, silage or swath grazing is recommended. Post-harvest regrowth can also provide some late-season grazing. This may be a little more complicated if you are a grain farmer as you will need to market the forage that you are producing.
For both the green manure and green feed options, one needs to look at the economics of not having a crop on the land, such as weed control and lost nutrients. On unseeded acres, the goal should be to cycle the nutrients and keep them there for next year.
The table below was taken from a Michigan State University factsheet. It provides some examples of the types of crops for unseeded acres that can be considered depending on what you goal is.
