By Hayford Gyamfi
Department of Renewable Resources, University of Alberta
Introduction
Perennial forages in one form or another provide feed to livestock all year round. In the Peace region, producers use several grasses and legumes in their forage establishments. In addition, grass-legume mixtures have been noted to increase yield and improve quality compared to grass monocrops. However, across Alberta, questions from producers focus on how to improve their pastures or hay lands using combinations of grass and legume species to optimize forage-livestock systems. Apart from the enormous benefits of perennial mixtures to the cattle sector, mixed perennial forages can also provide beneficial effects within the soil-plant ecosystems which include water use efficiency. The objective of this study was to examine a variety of grass-legume mixtures and compare them to grass monocrops in terms of their yielding abilities, qualities, and water use efficiencies (WUE).
What we did to evaluate the different perennial forage mixtures
The trial was established in 2020 at the Fairview Research Farm in Fairview, AB. The field had a history of several years of wheat-canola rotation for grain production.
Experimental design and seeding: The research was arranged in a randomized complete block design with four replications. The treatments comprised of six simple grass-legume (1 grass:1 legume) and 18 complex diverse perennial forage species (i.e.: 3 or more grass-legume) mixtures, thus 3 grass-only mixtures, 2 legume-only mixtures and 13 grass-legume mixtures. In addition, there were 5 pure stands of perennial grasses, which were used for comparisons (controls). The grass species used in mixtures and monocultures were wheat grass (kirk crested wheatgrass and Greenleaf pubescent), orchardgrass, timothy grass, meadow bromegrasses, and 2 hybrid bromegrasses (Table 13).
Seeding was done using the 6-row Fabro plot drill equipped with disc-type openers at 9″ on 2m wide x 8m long plots. Volumetric water content measurement was undertaken during the growing seasons of 2022 to aid in estimating the water-use efficiency of treatments.
In the first and second production years (2021 and 2022) forage dry matter (DM) yield was determined, and forage samples were analyzed for feed quality at A&L Canada Laboratory. The results for the first production year (2021) are available in the PCBFA annual report of 2021 (pages 50-53).
Our findings in the second production year
Forage DM yield and quality indicators of perennial forage for 2022
Forage yields were variably significant between treatments, ranging from 1,445 lb/ac for Mix 15 to 4,256 lb/ac for pure fleet meadow bromegrass (FMB). The top 5 highest yields were recorded in FMB (4,256 lb/ac), Mix 4 (3,631 lb/ac), Mix 14 (3,390 lb/ac), Mix 21 (3,480 lb/ac), and Mix 23 (3,346 lb/ac). Overall, monocrop grasses and “only-grasses” mixtures were poor in DM yield compared to grass-legume mixtures (Table 14).
Crude protein (CP): CP contents for all treatments were between 11 and 17% (Table 14). Grass-legume mixtures were generally superior to grass monocrops as observed in mix 1 (17%), mix 12 (16.7%), mix 14 (17%), mix 16 (16.6%), and mix 21 (16.6%) that contained both grasses and legumes. The number of legumes present in a particular treatment did not significantly affect the amount of CP in forage. CP contents in all forage treatments were adequate or even above adequate to meet the protein needs of beef cattle at different development stage (i.e., gestation, lactation, calving).
Neutral detergent fibre (NDF), Acid detergent fibre (ADF) and Neutral detergent fibre digestibility (NDFD-48hr): NDF across all treatments ranged from 44.2 to 57.6%, while ADF varied from 34.2 to 37.1%. Mix 14 and mix 16 were better in NDF (44.2 and 44.5%, respectively), while mix 13 ranked best in ADF (34.2%) when compared to all the other forage treatments. This makes mix 13, mix 14, and mix 16 the treatments with the lowest NDF and ADF, hence the best performers in terms of detergent fibre contents (Table 14). Furthermore, grass monocrops and all “grass-alone” mixtures recorded the highest NDFD (averagely 62.2%) compared to grass-legume mixtures. A higher NDFD will allow cows to eat more and digest efficiently to support their performance.
Total digestible nutrients (TDN): Energy levels in all forage treatments were above 60%. The highest %TDN was in grass monocrops and “grass-alone” mixtures such as orchard grass (67% TDN), timothy grass (67% TDN), mix 13 (68% TDN), and mix 15 (67% TDN). Notably, grass-legume mixtures were similar to grass-alone mixtures and pure grass stands (Table 14). The energy levels in forages are adequate to meet the requirement for dry pregnant beef cows (55% TDN mid pregnancy and 60% TDN at late pregnancy) and 65% for lactating beef cattle.
Water use efficiencies (for biomass and crude protein production)
The top performers for biomass WUE were mixes 4, 14, 21, and FMB. Among these treatments, mix 4 (76.3 lb/inch) and FMB (75.8 lb/inch) had the highest WUE (Table 15). Generally, grass-legume mixtures were better at using water efficiently to produce biomass compared to grass monocrops. Crude protein WUE significantly varied from 400 lb CP/inch for mix 15 to 1,185 lb CP/inch for mix 21. Overall, mix 14 (1,184 lb CP/inch), mix 21 (1,185 lb CP/inch), mix 22 (1,089 lb CP/inch), and mix 23 (1,082 lb CP/inch) had the highest crude protein WUE (Table 15).
Conclusion
The study has shown the forage yielding abilities and quality indicators of both grass-legume mixtures and grass monocrops and “grass-alone” mixtures. Generally, grass-legume mixtures were the highest in DM yield, CP and NDF while grass monocrops and “grass-alone” mixtures were better in ADF and %TDN. Even though several grass-legume mixtures contained different species of legumes, this did not seem to significantly influence the CP content. Furthermore, grass-legume mixtures were better at using water efficiently to produce biomass and crude protein compared to grass monocrops and “grass-alone” mixtures.
References
PCBFA 2021 Research. (2021). Progress Report on the forage production and quality potential and ecosystem functions of perennial forage mixes. Pages 50-53.
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