Seeding time has quickly come upon us. Naturally, the question of what to seed has either been answered, is close to being answered, or must be answered soon.
At least up here in the Prairie Provinces. Seeding time is from snow melt until the middle of June. The optimum tends to be around the middle to the end of May.
Nevertheless, this is not about when to seed but what to seed, especially when it comes to cover crops.
This very quick article gives a few little pointers on what a person should select when it comes to cover crops. This is a tall order, for me especially, because there’s a surprisingly huge amount of information and choices to be made when choosing what species to sow.
My first tip is to use the process of elimination. When you have a big list of species to choose from, whittle down on it by figuring out what purpose they serve and which are most likely to help you the most.
How do you do this? First, we need to understand the purpose of most plant functional groups. Cover crops are primarily made up of annual and/or biennial plants and one to over a dozen different species and/or plant families.
Different Plant Functional Groups
A fantastic book by Kevin Elmy called Cover Cropping in Western Canada helps simplify concepts like “plant functional groups.” He explains that there are four primary functional groups we need to know about: the grasses, the legumes, and the group of broadleafs that are either brassicas or non-brassicas. (“Forbs” are identified as legumes, brassicas, and non-brassicas. However, for simplicity’s sake and to help identify which species are needed, it’s more useful to identify which are legumes and which are not, and which are brassicas and which are not.)
We can further divide these four primary functional groups into warm-season plants and cool-season plants.
Grasses are best known for their fibrous roots and ability to recycle nitrogen and add organic matter to the soil. They form great relationships with mycorrhizal fungi. Oats, barley, corn, ryegrasses, rye, wheat, teff grass, triticale, and sorghum-sudan are examples included in cover crop mixes.
Most forbs are tap-rooted. Some are better than others, like brassicas versus other forbs or “non-brassicas.” Many also develop lateral, somewhat fibrous roots that branch out from their primary tap-root. However, they don’t compare to grasses.
Forbs grow either laterally (creeping and covering the ground), vertically (growing erect), or climbing on other plants. They can have massive wide leaves or groups of small leaves. Forbs include legumes, which form relationships with rhizobacteria to capture and utilize nitrogen. Others take excess nitrogen in the soil and recycle it after dying.
Legumes are a cheaper means to take free nitrogen from the atmosphere and essentially “put it back” in the soil to be utilized by other plants. Beans, peas, vetches and clovers are common in cover crops, as are lentils and chickpeas.
Brassicas are best known for their wide and deep taproot, which is usually great for breaking up the hardpan (provided it’s not too densely packed). They don’t form good relationships with mycorrhizal fungi and can pick up diseases still in the soil from a previous brassica crop (like canola). However, they are great at recycling nitrogen and break down fairly quickly when there’s a hard frost. Diakon and tillage radishes, mustard, forage rape, forage collards, and turnips are examples.
Other “non-legume” and “non-brassica” forbs are everything else that can be thrown in a cover crop mix. Buckwheat, phacelia, chicory, plantain, sunflower, sugar beets, and safflower are commonly used in cover crops.
Now that you know your options are much more numerous than just either soybeans and corn or wheat and canola, the question of “what should I use” ultimately depends on various factors we’ll discuss next.
What’s Your Context?
What type of cover crop mix you can plant depends on the land you’re farming and the environmental constraints that are placed upon it. For example, if drought and sandy soils are a regular thing for your operation, you probably don’t want to seed perennial ryegrass as it won’t grow nearly as well as something like teff grass, which is both drought and heat-tolerant. On the other hand, what you had last year could impact this year’s crop regarding disease risk. Planting lots of brassicas in a field that previously had a canola crop can further exacerbate disease spread. Finally, what you’re willing to spend and who can supply your seed (and what types) also limits what you can put on the land. Keep these in mind as you answer the following questions:
- What type of farm are you operating?
- Conventional or organic?
- Grain only, livestock only, or mixed?
- What moisture regime do you deal with?
- Too dry, too moist, or just fine?
- What soil texture is common on your farm?
- Sandy soil
- Loam
- Clay soil
- What soil fertility are you dealing with?
- Low fertility, medium, or high?
- What was the previous crop sown last year?
- This will influence crops chosen based on disease pressure, herbicide residue, etc.
- Who is supplying your seed and how much are you willing to spend?
What Are Your Future Plans?
Next, we look at what you plan to do with the cover crop and afterward. If you want to harvest for hay and/or grazing rather than plowing down, consider a mix that has good regrowth potential so that you have some forage available for your animals later in the year. Seeding impacts how much growth you can get above and below ground (remember, roots are important).
How you seed is also important, especially when dealing with different seed sizes. For example, seeding a cover crop of big (oats, barley, corn) versus small (buckwheat, clovers, radishes, ryegrasses) seeds can be challenging because the big seeds can bung up a lot of small seeds if sown together, causing uneven seed distribution. Consider seeding the big ones separately from the small ones by either having them in different compartments or seeding the big seeds first, then going over the seedbed again in a second pass with the small seeds. Big seeds need to be sown deeper than the small, so this can make a big difference in success rates of not only germination but plant distribution!
- What are your end goals for this cover crop?
- Hay/silage or grazing?
- Green manure or soil improvement?
- Ground cover with a cash crop?
- Relay crop after cash crop harvest?
- Intercropping with a cash or feed crop?
- When do you want to seed this cover crop?
- Early spring or late spring?
- Early summer or late summer?
- Early fall?
- How do you plan to seed? What equipment do you have or can you borrow?
- Broadcast?
- Drilled?
- Or a combination of the two?
- How do you plan to terminate the crop?
- Cultivation and/or herbicides?
- First frost or last frost?
- Over-wintering?
- Grazing or Hay/Silage?
What Are Your Resource Concerns? What Issues Are You Facing?
From the worst to the least, the top two concerns that I’ve helped producers with are Weeds and Low Fertility. Bottom line: Weeds are always on the top of the list to combat using a cover crop (or at least try) because it’s getting expensive to use herbicides every year to combat the same weed species that like to come up every year.
Poor fertility (including low nitrogen) comes a close second. One, because fertilizer prices are now stupid-expensive (I was told nitrogen fertilizer is more than $1,200 per ton, double what it was five years ago), and two, soils have been farmed to the extent that fertilizer is a basic necessity if a crop is to be grown and harvested in the first place. So, what better “silver bullet” to help solve the fertility issue than a cover crop?
(Except, it’s not a silver bullet; it’s just a tool in the toolshed…)
What other issues are out there that you need to start fixing using a cover crop mixture? Let me name some more:
- Hardpan: otherwise known as a soil plow layer, or compaction.
- Poor aggregation: meaning that the soil is packed such that it won’t let water and air in or out.
- Slow infiltration: see #2 above. Water is sitting on the soil surface or running off into the lowest points on the field, instead of quickly soaking in.
- Weeds: see above. To take it a step further, identify what weeds are a “problem.” Dandelion? Lambsquarters? Kochia? Chickweed? Thistles? Pigweed (of the Amaranth family)? Quackgrass? List them!
- Low N (nitrogen): see above.
- Erosion: the soil is easily blown away by the wind or washed away by water, not protected and not held in place by either organic matter or living roots.
- Low OM (organic matter): it’s not just the soil lacking that protective shield on top, it’s also what’s in the soil. Lack of dead root and plant matter in the soil usually means slow infiltration, poor fertility, anaerobic microbial activity versus aerobic, and other issues.
- Low fertility: see above. Also leans toward an imbalance of soil nutrients, not necessarily low fertility per se. Weeds are often a sign of certain imbalances, like too much phosphate or not enough calcium.
- Grazing: The only concern is if grazing land is likely to not be available in the summer and a crop is needed to help sustain the herd until late summer or fall.
- Hay/Silage: The need for winter feed is important!!
- Salinity: Too much salt limits productivity in certain areas. A high water table or water that remains in the bottoms and evaporates leaves salts behind, making the area less and less suitable for plant growth. This is a common issue on the prairies of dark brown or brown [chernozemic] soils. The use of salt-based fertilizers and pesticides may also be a cause of salinity issues.
Identifying even just a few on this list will help narrow down what species you might need in your mix, and eliminate the ones you don’t need.
Conclusions: What Should I Seed?
The beauty of cover crop mixtures is that the possibilities are endless in what you can use in your mixture. You can be as simple as two species or as complex as over 20 species. There’s no best mixture for every farm: what is best is only that which fits your context.
It can be seen in two ways: both freeing and overwhelmingly challenging. Freeing because you’re given free rein to just try something new, whatever you want or you think, based on all those mentioned above, that fits your farm. Overwhelming because there are so many to choose from that it can be to the point of “paralysis by analysis”!
Like I said before, start by understanding your needs and limitations (i.e., your context). Then, figure out your biggest, most problematic issue[s] (two or three at the most; one if two or three doesn’t cut it). Get a sense of your primary functional groups: grasses, legumes, brassicas and non-brassicas. Out of these, which do you need the most: the fibrous roots, the scavengers, the ground coverers, the nitrogen fixers, or the bee attractors…? Then, figure out what you need the most or a mix of: cool-season plants and/or warm-season plants. Which are you needing more out of based on when you planted and when and how you want to terminate? Finally, what is actually available that your seed supplier can sell to you?
Check off which are ideal and which you should not think of again. From there, your list will get smaller and smaller until you have a select few species to use.
Good luck, and have fun!