Soil carbon and nitrogen fractions as affected by soil physical disturbance in grazed legume-grass pasture systems
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Date
2020-03-10
Authors
Issah, Gazali
Schoenau, Jeff
Lardner, Bart H.
Knight, J. Diane
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Abstract
Tillage, like any other form of forage termination, is frequently employed to regenerate the productivity of a pasture stand or prepare the land for annual cropping. Tillage alone, or in combination with other forage termination methods, has proven successful as part of the process in rejuvenating old pasture stands. However, the effects of tillage on C and N fractions in the short-term have not been determined in long-term pasture systems in western Canada. The objectives of this study, conducted at the Western Beef Development Centre (WBDC) at Lanigan, SK, were to determine the impacts of tillage on C and N fractions in legume-grass pastures containing three different legume species: alfalfa, cicer milkvetch and sainfoin. Tillage was imposed in the fall of 2018. The tested hypothesis was that the disruption of soil aggregates through tillage would increase microbial respiration and organic C loss. In the sprin g of 2019, no significant measurable effect on total, light fraction and dissolved organic C and N were observed. However, by the summer of 2019, dissolved organic N was reduced due to the tillage operation (p<.0001). Microbial biomass C (MBC) was lower in tillage treatments in both the spring (p=0.0002) and summer (p=0.0027). The aggregate disruption that occurred with tillage in the fall may have increased initial decomposition, followed by a decrease in microbial populations and activity later in the season. There was no apparent effect of legume species on the C and N fractions after one growing season. The trend suggests that all the legume species evaluated may similarly respond to a disturbance.
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tillage, forage termination, pasture, pasture regeneration, rejuvenating old pasture stands, impact of tillage on C and N fractions
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Soils and Crops Workshop