Perennial polycultures and Managed Intensive Rotational Grazing (MIRG)
By Lydia Carpenter - Manitoba Eco-Journal
Permanent Pasture stands can be maintained by use of perennial polycultures that imitate the diversity of natural ecosystems. A diverse grouping of plants consisting of grasses, forbs, and woody species can make up a perenni- al polyculture and be used as pasture for grazing animals (ruminants), including cattle, sheep and goats. Animals on a perennial polyculture can contribute to nutrient cycling and an increase in soil organic matter. Established, maintained and healthy perennial pastures have also been shown to have a large capacity for carbon sequestration.
On our farm in Western Manitoba, we have counted over 30 different species of both native and non-native perennials and biennial forages, including nitrogen-fixing legumes such as alfalfa, pea-vine and various species of clover. These plants populate our permanent pasture that maintains a flock of sheep, a herd of goats and seasonal pro- duction of pasture-raised poultry.
We employ a Managed Intensive Rotational Grazing (MIRG) system that calls for short periods of grazing or “disturbance” followed by a recovery period. In our MIRG system the sheep and goats graze together, with the goats preferring to eat more browse (such as twigs and shoots), and the sheep showing preference for forbs and grass. For the sheep and goats, portable electric fenc- ing is used to create pasture paddocks. The goats and sheep are moved every few days and are fol- lowed by the chickens. The chickens are moved daily in portable pasture poultry pens.
It is not enough to move animals from one pasture to another. Stocking rates (number of animals per unit of land as a function of density and time) and rest periods are critical in manag- ing animal nutrition, plant re-growth, nutrient distribution, and interruption of pathogen life- cycles. Studies have demonstrated that at both the plant and community levels, primary production increases for grazed vegetation above ungrazed vegetation where an optimal stocking rate is fol-
lowed by a rest period. Moreover, periodic cessa- tion of grazing, especially during periods of rapid growth, will enhance both shoot and root growth by promoting the recovery and maintenance of greater leaf area. In this type of grazing system both plant biomass, and livestock manure and urine, lead to increased soil organic matter and a potentially more complex soil food web.
Management goals and local ecological con- straints determine the success of any MIRG sys- tem. Many MIRG practitioners aim to integrate farming with the local ecology and increase plant biomass and soil organic matter. In addition, oth- ers may aim to raise healthy, grass-finished animals without the use of growth hormones or antibiot- ics. While the principles of MIRG may be univer- sal, climate, soil, and local ecology inform varying management practices. As we seek to orientate food production into more resilient systems, it is important that we seek out traditional and local knowledge and contribute to a sense of place.
Nutrient Cycling: “Animals on a perennial Filling the gaps and closing the loop polyculture can contribute Nitrogen, Phosphorus and Potassium (N, P to nutrient cycling and an and K) are some necessary elements for healthy productive plants, from market gardens and pasture, to canola and soy. In agriculture, nutrients are acquired and applied on the land in several ways. N, P and K are derived from mining fossil fuels (oil sands and potash mines), green ma- nure crops on cultivated fields and manure/ humanure (animal feedlots and municipal waste).
In some MIRG systems animals are kept out on the land year round to distribute their nutrients in a rotational system. It is important to note that MIRG can be done in the winter months with the use of techniques like bale grazing, swath grazing and mechanized winter-feeding on pasture. Not only does this mean the animals may live outdoors and outside of confinement but this strategy also allows for decreased overhead costs for both N,P and K, and the machinery and fuel needed for polycultures is often less expensive than cultivated land. Furthermore, MIRG can be done as part of a ”larger strategy that seeks not only to raise healthy livestock and create healthy pastures and soils, but to reduce the use of fossil fuel inputs, food miles, antibiotics, growth hormones, GMOs, grain feeds etc. MIRG systems combined with direct farm marketing of grass-based livestock are one way for application. In a rotational grazing system much of the needed N, P and K are added or recycled to pasture via the manure and urine of livestock.
Our farming is fuelled by an interest in community, ecosystem dynamics, material and nutrient (re)cycling and renewable energy. MIRG allows us to look at ecological systems and see ourselves in them, not outside of them. As part of our own ecology we must learn how to navi- gate the dichotomies of life and death. Our agri- culture is informed by a privileged environmental ethic that has brought us closer to both.
Lydia Carpenter and her partner Wian Prinsloo run Luna Field Farm, a pasture-based farm 20 miles south of Brandon.