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Journal of Animal Science Abstract - Animal Production

Carbon flux assessment in cow-calf grazing systems1

 

This article in JAS

  1. Vol. 93 No. 8, p. 4189-4199
     
    Received: Feb 20, 2015
    Accepted: June 01, 2015
    Published: July 24, 2015


    2 Corresponding author(s): marilia.chiavegato@usp.br
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doi:10.2527/jas.2015-9031
  1. M. B. Chiavegato 2*,
  2. J. E. Rowntree and
  3. W. J. Powers
  1. * Department of Animal Science, University of São Paulo, Av. Pádua Dias, 11, Piracicaba, SP 13418-900, Brazil
     Department of Animal Science, Michigan State University, 424 S. Shaw Lane, East Lansing 48824

Abstract

Greenhouse gas (GHG) fluxes and soil organic carbon (SOC) accumulation in grassland ecosystems are intimately linked to grazing management. This study assessed the carbon equivalent flux (Ceqflux) from 1) an irrigated, heavily stocked, low-density grazing system, 2) a nonirrigated, lightly stocked, high-density grazing system, and 3) a grazing-exclusion pasture site on the basis of the GHG emissions from pasture soils and enteric methane emissions from cows grazing different pasture treatments. Soil organic carbon and total soil nitrogen stocks were measured but not included in Ceqflux determination because of study duration and time needed to observe a change in soil composition. Light- and heavy-stocking systems had 36% and 43% greater Ceqflux than nongrazed pasture sites, respectively (P < 0.01). The largest contributor to increased Ceqflux from grazing systems was enteric CH4 emissions, which represented 15% and 32% of the overall emissions for lightly and heavily stocked grazing systems, respectively. Across years, grazing systems also had increased nitrous oxide (N2O; P < 0.01) and CH4 emissions from pasture soils (P < 0.01) compared with nongrazed pasture sites but, overall, minimally contributed to total emissions. Results indicate no clear difference in Ceqflux between the grazing systems studied when SOC change is not incorporated (P = 0.11). A greater stocking rate potentially increased total SOC stock (P = 0.02), the addition of SOC deeper into the soil horizon (P = 0.01), and soil OM content to 30 cm (P < 0.01). The incorporation of long-term annual carbon sequestration into the determination of Ceqflux could change results and possibly differentiate the grazing systems studied.

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