I am a big fan of diversity in both perennial and annual grazing situations. In some ways multiple species are more difficult to manage than less-diverse plant communities. In a multi-species scenario every action and in particular its timing will favour one species over another and shift the balance of power in the pasture.
The flip side of that is that well-designed multi-species pastures will have a diversity that increases overall yield, improves diet composition and reduces the risk from a variety of weather and production challenges.
I always think about the ground as being like the surface of a mirror. What we see above ground is a reflection of what is going on below. At its most basic and simplified level, the parts of a plant that are above ground absorb sunlight and use the solar energy to convert carbon dioxide (yes, the taxable kind) and water into sugar. The sugar is then sent underground to feed bugs and fungi. They work with the roots to pull in nutrients like nitrogen, phosphorus and water for the plant to use for constructing proteins and other things that are not simple sugars.
When working well, this is an extremely productive partnership. Worth mentioning in this process is the special role of legumes, which also pull nitrogen gas from the air and send it underground where bugs are converting it into plant-useable forms of soluble nitrogen. The fungus and bugs then steal this nitrogen for plants that can’t make their own.
With this basic outline, it makes some sense that we want as much solar collection capacity above ground as possible and conversely we would like as much root capacity as we can get below ground. Additionally, since we have a limited number of days to capture solar energy we want a variety of plants that peak in growth from April/May through to September/October, or at least a spectrum of pastures that peak at different points of the year.
Different plants have different growth profiles. Some are taller (wheatgrasses), some are shorter (bluegrass), some are green early in the spring (think crested wheat), some are better in the fall (Russian wild rye), some are nitrogen fixers (alfalfa, clover) and the list goes on. The important point is that each plant or plant species can cover different areas both above and below ground.
Think of an umbrella
While we may not be able to have a plant stem growing out of every square inch of soil, having a variety of plants in a stand allows the leaf canopy to cover more than the ground. A good analogy is an umbrella (perhaps not on the Prairies, but it is the picture that is important). The handle of the umbrella only covers a small portion but the canopy when opened covers a much greater surface area. If we planted umbrellas that grow to different heights it is possible to have the canopies overlap and cover over 100 per cent of the surface area of the ground they are over.
Ideally the goal with a plant community should be to try to cover the ground 300 per cent or more with active solar-capturing leaves. To do this we need a variety of plant height, leaf shape and stem structures.
It is good to think about the underground aspect of our pasture in the same way. A simplified example of the root zone issue is on a lot of the commercially available alfalfa blends. Many are sold as creeping rooted, tap rooted and rhizomatous. This helps to distribute roots throughout various levels of the soil profile and provides an advantage across various weather situations. The same applies to grass species.
Accommodating field variability
One of the other major reasons to consider multi-species grazing is the fact that most landscapes have some variability. Low spots may have more moisture or organic matter levels. Even soil type may vary in a single field. Including multiple species in a grazing mix helps to ensure that various areas are growing forage. It is not uncommon to see variation in relative plant species density across a pasture, even when it was all seeded to the same mixture and managed in the same way.
Multi-species mixes can help manage saline areas, sandy soils, slope or standing water. The gradient of species is much more effective in maximizing forage production than a human-defined line. For example, soil types may change gradually over the slope of a hill and there may not be a defined line between the conversion from sand to clay. A multi-species pasture will have a gradual change in species composition up the slope, rather than a start/stop line between species.
Another key reason for multiple species is outside of direct production but can have an indirect effect on productivity. Multiple species and a patchwork of plants creates a patchwork of habitats for different wildlife to survive and thrive. This does not just include large animals, but also smaller animals like birds and bugs. While we often don’t like to think about bugs in a positive way, there are a lot of insects that provide pretty valuable services such as cleaning up various worms and larvae of species that are harmful to our livestock or forage production, or accelerating the decomposition of manure into plant-available nutrients. Fly and grasshopper eggs on a poop plate anyone?
One of the interesting things I see time and again in our pasture-monitoring program is the difference in plant density and diversity in native versus tame plant communities. No matter what method I use to seed or graze tame stands, I have not been able to achieve the plant densities in our native stands and I am certainly not talented enough to figure out how to achieve the plant diversity that is present in our native ecosystems. Native stands are very resilient and it is this resiliency that is the greatest asset in an established, tame forage stand. From drought resistance to biodiversity to increased production, multi-species plant communities are worth the extra management effort.
While certainly blanket rules create exceptions there are probably two or three basic guidelines worth stating.
- Every stand needs a legume. Legumes fix nitrogen and help feed soil biology and other plants in the stand. Examples that we have used in tame stands include alfalfas, clovers and vetches. We have started using hairy vetch (an annual) as an addition to our swath grazing as well. For those worried about bloat, consider using a lower percentage of legume or adding sainfoin to the mix.
- We need to grab as much sunlight as we can over the year. This means we need species that respond to sunlight at different times, with a variety of growth patterns. A good example would be the difference between crested wheat (early growth), bromegrass (mid-season growth) and Russian wild rye (late season). Even our annual crops include a variety of spring and fall/winter cereals in an effort to capture every ounce of sunlight we can get.
- We need to cover more ground above and below with a variety of structures. The plant canopy needs to cover more than 100 per cent of the area of the ground and the roots need to cover as much of the soil profile as possible. Remember that shoots build roots, and roots build shoots.
- We need to pay attention and manage for the species we want. Because a multi-species system can be complex, we need to watch with particular attention to weak links and warning signs. This could include reduction in prevalence of a preferred grazing plant, loss of litter or bare soil.