Submitted to: Symposium Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 6/10/2003
Publication Date: 6/10/2003
Citation: FOLLETT, R.F. PASTURE MANAGEMENT SYSTEMS: IMPACT ON SOIL CARBON AND GREENHOUSE GASES. SYMPOSIUM PROCEEDINGS. 2003. CD-ROM. Interpretive Summary: These data indicate that soil carbon sequestration efficiencies need to approach or exceed 10%, N fertilization can be 90 kg N ha-1 yr-1, and stocking rates can be about 150 steer-days/ha/yr before a positive (increased) greenhouse warming potential occurs. The most important factor for minimizing net GHG emissions is to obtain a balance between the influence of N-fertilizer use and management to enhance SOC sequestration. Minimizing the N2O emissions that result from the N-fertilizer use is needed but sufficient fertilizer is needed to obtain optimum forage production and optimum livestock grazing rates so that enteric methane emission from livestock is not excessive.
Technical Abstract: This paper considers the issue of soil organic carbon (SOC) sequestration in US grazing lands and factors that affect both the loss and accumulation of C in soils. The paper then addresses a hypothetical greenhouse gas (GHG) budget analyses for a pasture system that is fertilized at three nitrogen rates and grazed at three rates by steers. Because no single study was available where such GHG measurements have been made, the estimates obtained in this analyses are based upon data from a number of past and present studies from various locations, national assessment information, published or measured conversion factors, interviews and finally necessary assumptions to make the estimates. Within the boundaries of a one-ha pasture comparisons were made of potential rates of SOC sequestration and methane uptake by soil; emissions of carbon dioxide from nitrogen (N) fertilizer manufacture, transport, and spreading; and nitrous oxide emissions from N fertilizers and excreted urine and feces. For this example, these data indicate that soil carbon sequestration efficiencies need to approach or exceed 10%, N fertilization can be 90 kg N ha-1 yr-1, and stocking rates can be about 150 steer-days ha-1 yr-1 before a positive (increased) greenhouse warming potential occurs. The most important factors for minimizing net GHG emissions are to obtain a balance between the influence of N-fertilizer use and management to enhance SOC sequestration and the N2O emissions that result from N-fertilizer use, and enteric methane emission by grazing livestock.