By Treena Hein
Managed permanent pastures are something that many crop farmers have – and the productivity of these pastures is closely associated with what species mixtures are planted and how many species are present. “Ecological theory suggests that increasing the diversity of plant species in an area will provide higher productivity, resilience and resistance to invasive species, and we wanted to investigate this concept with mixed-grass forage species,” explains Yousef Papadopoulos, a crop scientist at Agriculture and Agri-Food Canada (AAFC) and an instructor at the Nova Scotia Agricultural College in Truro, Nova Scotia.
By Treena Hein
According to the 1996 census, there are 15.4 million hectares of pasture in Canada. “More than half of the pastures in the Atlantic provinces consist mainly of permanent pastures,” says Papadopoulos. “In my estimation, there are approximately 4000 beef and sheep farms in the three Maritime provinces and on average, each of these farms will have 40 to 50 acres of permanent pasture. Therefore, I believe the total acreage of permanent pasture in the Maritime provinces exceeds 160,000 acres.”
Although all the mechanisms aren’t yet understood behind the fact that plant communities with more species and more diversity of species are generally more high-yielding and stable than those with fewer species, the difference is significant. “Natural grasslands are more resilient, for example, to stresses like drought than cultivated stands of lower species diversity,” notes Papadopoulos. “It’s known that highly complex pasture swards have higher shoot and root biomass, as well as higher photosynthetic rates compared to simple ones.”
This is good news for farmers. Papadopoulos notes that pasture production is one of the few agro-ecosystems where the level of plant diversity can be managed, and it’s therefore unique in that the benefits of biodiversity can be used to create a stable ecosystem capable of delivering forage consistently over the season. “However, in order to accurately assess the importance of species diversity,” he explains, “the effects of individual species must be singled out, and studies done so far have not measured combined benefits of species mixture and number of species.” For example, some pasture studies show that the positive effects of diversity are the result of the presence of a single species, such as the presence of N-fixing clovers in an N-limited pasture.
This is why Papadopoulos (with colleagues Michel McElroy and Alan Fredeen at the Nova Scotia Agricultural College, Sherry Fillmore and K.B. McRae at AAFC’s Atlantic Food and Horticulture Research Centre in Kentville, Nova Scotia, and John Duyinsveld at AAFC’s
Atlantic Food and Horticulture Research Centre in Nappan, Nova Scotia, has investigated the effects of pasture species mixture – as well as the number of species within the mixture on pasture productivity. “We varied the number of perennial grasses in small plots that were then grazed for five years,” he notes, “and we also sought to identify specific mixtures that retained high productivity after stand establishment.”
The team seeded mixtures of four common pasture grass species – timothy, Kentucky bluegrass, reed canarygrass and meadow fescue in 2004 in Truro, Nova Scotia, in two-grass, three-grass and four-grass combinations with white clover. “Plots were rotationally grazed for five years, with dry matter yield (DMY) determined in the first post-establishment year (2005) and in three subsequent production years (2007, 2008, and 2009),” explains Papadopoulos.
Results of study
The team found that the number of seasons – and both the mixture and number of species – have important effects on the productivity of rotationally grazed pasture systems. The average DMY for two-grass plots was significantly lower than for all others pastures, Papadopoulos explains, because only two plant species cannot efficiently utilize available soil and light resources. With regard to seasonal results, the team found yields in the post-establishment year were much lower than in subsequent production years, but this is not unusual for a perennial pasture. Over the latter production years, the four-grass plots produced significantly higher seasonal DMY compared with all other plots. “Our results showed that it may take up to three years before a newly seeded pasture reaches full potential,” Papadopoulos says, “meaning the compatibility of the stand becomes fully developed, maximizing the use of available soil and resources while maximizing sunlight interception.”
Aside from the single four-grass mixture being a significantly better performer, no other specific mixture of any of the grasses was better than any other. “However, timothy- and bluegrass-containing plots over production years did do a little better in terms of seeded grass growth and DMY,” Papadopoulos notes. “We also found that the growth of unseeded grasses and forbs increased in mixtures with large proportions of timothy and reed canarygrass.” However, in spite of the fact that mixtures containing timothy and bluegrass were shown to produce high DMY, the aggressiveness of bluegrass appeared to suppress the yield potential of timothy. “White clover yields and unseeded grasses/forbs were also both significantly lower in mixtures containing bluegrass,” he says. “We also found a favourable compatibility between meadow fescue and white clover growth, while bluegrass appears to suppress meadow fescue growth.”
“From this study, it seems that the positive effects of biodiversity on yield are in large part due to whether or not timothy and bluegrass were present in more complex mixtures, but the more species, the better the yield as well,” says Papadopoulos. “So, in recommending what farmers should do to achieve long-term, low-input productive pastures, I would say from this study that they should plant all four grass species with white clover.”
He notes that creating a forage stand that will remain productive for many years depends on selecting a compatible and well-adapted mix and managing these species to make best use of their attributes. “Furthermore, a sward comprised of several adapted species will make efficient use of available resources throughout the growing season, slows encroachment by invasive species, and is more likely to perform well under a wide range of environmental conditions.”
This study confirmed the benefits of complex mixtures in pastures, but Papadopoulos says he and his colleagues have yet to identify which species now recommended in Canada should be included in those complex mixtures for the very diverse climatic conditions of Eastern Canada and for the different grazing management strategies. “Our research team is currently studying several complex mixtures in five locations in Nova Scotia, Quebec, Ontario and Manitoba,” he says.