Pasture mixtures of grasses and legumes for the long-term sustainability of beef production
- Determine the long time (3-5 years) agronomic performance of different simple and complex grazed grass-legume mixture along with associated beef performance
- Evaluate the effect of N fertilization on yield, nutritive value and persistance of complex pasture mixtures
Although most forage produced in Canada is comprised of species mixtures, there is limited research on identifying the best species, and cultivars, to include within forage mixtures. In Experiment 1 the long-term agronomic performance of binary mixtures of one of three legume species and one of three commercial cultivars of six grass species was studied. Grasses were timothy, Kentucky bluegrass, tall fescue, orchardgrass, meadow fescue, and meadow brome. Legume species were birdsfoot trefoil, alfalfa, and white clover. Each grass species was subdivided into a set of one (both Quebec sites) or three (Nappan) cultivars. At Lévis and Normandin, grazing was simulated; at Nappan, mob grazing with beef cattle was used. The grass species in mixture with all legumes persisted well under frequent cutting or rotational grazing but their performance varied with sites. White clover grown with any grass species did not perform well under frequent cutting or rotational grazing. At all trial sites meadow bromegrass-based binary mixtures had the greatest DM yield with alfalfa or birdsfoot trefoil.
Legume, grass species, and grass cultivars in the mixture significantly affected annual dry matter yield (DMY). High regrowth yielding binary mixtures with average or below average ADF and aNDF concentrations across the four years in Atlantic Canada included white clover cv ‘Milkanova’ and Kentucky bluegrass cv ‘BG3’, birdsfoot trefoil cv ‘AC Langille’ and tall fescue cv ‘Kokanee’, alfalfa cv ‘CRS1001’ and Kentucky bluegrass cv ‘Ginger’ and alfalfa cv ‘CRS1001’ and tall fescue cv ‘Kokanee’. White clover binary mixtures had the greatest seeded legume plant counts over the four years, but generally showed the least legume contribution to yield. These results indicate that the choice of grass species, grass cultivars, and legume species in binary grass-legume mixtures affect forage yield and the survival of grass plants in grazed swards.
In Experiment 2 with complex pasture mixtures, cattle grazing (AAFC Nappan site) trefoil pastures had over 40% greater animal gain per hectare than cattle grazing alfalfa based pastures, and had slightly better average daily gains. This was despite higher dry matter yields, TDN, and CP levels in the alfalfa pastures. The trefoil pastures showed higher water soluble carbohydrates and WSC/CP. Pasture mixtures containing timothy showed greater animal daily weight gains than those containing tall fescue. Agronomic results for the complex mixtures from across all sites showed significant grass mixture by legume by site interaction. In general the sites in Quebec showed a greater drop in DMY over the 5 years compared to the Nappan site, likely due to the nutrient cycling associated with the cattle grazing. In all sites the legume levels showed linear declines in yield, greater at the Nappan site, likely due to selective grazing by the cattle.
In Experiment 3 the effect of N fertilization on yield, nutritive value, and persistence of complex pasture mixtures was evaluated. In general, increasing N fertilization of complex mixtures did not increase the seasonal forage dry matter (DM) yield at any of sites in the first post-seeding year but generally increased the seasonal DM yield in the second and third post-seeding years. Nitrogen fertilization increased the N concentration of the forage and decreased its non-structural carbohydrate concentration. The legume species (alfalfa and birdsfoot trefoil) affected seasonal DM yield and some nutritive attributes only in the first post-seeding year. The low contribution to DM yield of the two legume species in the second and third post-seeding years (< 30%) explains the lack of an effect of legume species on most attributes.
Increased animal gain per hectare of over 40% was shown by using trefoil as opposed to the commonly used alfalfa, despite the fact that alfalfa as a legume in complex mixtures had greater dry matter yield, protein content, and total digestible nutrients. The results of the animal trials indicate a strong relationship between water soluble carbohydrates and animal gain as well as animal productivity per hectare. Complex mixtures with timothy and meadow fescue showed a greater average daily gain than those with tall fescue. However, those with tall fescue had similar animal gain per hectare. This suggests that for pasture situations where individual animal performance is a priority, timothy and meadow fescue with trefoil would be desirable; if overall gain per hectare is the primary need for a larger number of cattle with lower production expectations, tall fescue based pastures may be more suitable.
Regarding the selection of forage species and cultivars for use in pastures, it is clear that some species and in particular, cultivars within species, will give greater yield and nutritional quality. Although several grass species cultivar/legume combinations are highlighted, from a national perspective these results demonstrate that evaluating species and cultivars under grazing systems would benefit the beef industry.
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