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Effects of novel non-bloat legumes on C and N pools in pasture systems




Issah, G.
Schoenau, J.J.
Knight, J.D.

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Improved pasture systems have the potential to reduce greenhouse gas (GHG) emissions and enhance soil organic carbon (SOC) to mitigate climate change. However, with intensive grazing, pastures can lose a considerable percentage of stored SOC because of lowered primary production and increased soil erosion. Degraded pastures with N-limited soils can be regenerated either through fertilization at soil-test recommended rates or inclusion of legume species such as alfalfa. Despite the predominant use of alfalfa in pasture regeneration within North America, its economic benefits for cattle are not fully realized because of frothy bloat leading to the inefficient use of its protein value. Therefore there is a renewed interest in novel non-bloat legumes such as Sainfoin and Cicer Milkvetch as alternatives. In spite of the successful use of Sainfoin and Cicer Milkvetch in pasture regeneration, their impacts on SOC and C sequestration have not been determined. The objective of this study as part of a broader study was to determine the effects of novel non-bloat legumes inclusion using the sod-seeded technique on labile and bulk C and N pools. The study hypothesized that; the inclusion of novel non-bloat legumes with different N2-fixation and photosynthetic capabilities in pasture systems could increase both labile and bulk C and N pools due to increased soil organic matter content and microbial population. After two years of incorporating non-bloat legumes in pasture systems, preliminary results showed SOC was significantly (P <.0001) higher on the upper slope compared to the lower slope position. The system can store between 45.1 ±5.47 to 75.7 ±4.21 Mg C ha-1, in the lower and upper slope positions, respectively, up to 1 m soil depth, with 50% of the SOC within the top 0-30 cm soil depth. Light fraction organic C and N, and dissolved organic C and total N followed the same trend as the SOC with upper slope position recording higher values compared to lower slope position. Baseline soil nutrients also proved that the pasture system has a closed nutrient cycling. Finally, irrespective of the legume species or cultivars, the C: N ratio is close to 10:1, suggesting a dynamic equilibrium may be due to the dominating presence of a microbial population. The closed nutrient cycling and the near equilibrium C: N ratio shows that after two years of pasture rejuvenation, the inclusion of non-bloat legumes using the sod-seeded technique has the potential to improve forage quality and reduce GHG emission footprint of pasture systems. Results would add to that of a broader study and would be beneficial to producers and policymakers within Canada and beyond for C accounting and credit purposes.










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Soils and Crops Workshop