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Global Climate Change Digest
A Guide to Information on Greenhouse Gases and Ozone Depletion
Published July 1988 through June 1999

FROM VOLUME 11, NUMBER 10, OCTOBER 1998

PROFESSIONAL PUBLICATIONS...
MITIGATION

Climatic Change devoted a special issue to the topic of the mitigation of greenhouse gases by the agricultural sector:

Item #d98oct4

“Mitigation of Greenhouse Gas Emissions by the Agriculture Sector,” N. J. Rosenberg (Pacific Northwest National Laboratory, Washington, D.C., 20024), C. V. Cole, Keith Paustian,Clim. Change 40 (1), 1-5 (1998).

The editors survey and summarize the articles in this special issue and conclude that emissions of N₂O and CH₄ can be substantially reduced by practices that simultaneously increase productivity and that the sink for carbon in soils can be substantially increased. They also feel that further improvements in mitigation techniques could be developed with additional research. A major problem is how to encourage the adoption of mitigation techniques. They point out that greater attention must be devoted to understanding socioeconomic and political impediments to that adoption and urge the IPCC to place greater emphasis on this aspect of the problem.

Item #d98oct5

“Assessing and Mitigating N₂O Emissions from Agricultural Soils,” A. R. Monsier (USDA/ARS, Fort Collins, CO, 80521) et al., Clim. Change 40 (1), 7-38 (1998).

Agricultural systems are estimated to produce about one-fourth of global N₂O emissions. Methods that could mitigate these emissions include increasing the productivity of agricultural lands, lengthening the rotation times of shifting agriculture, managing grasslands, incorporating crop residues into the soil, using crop residues for household fuel, shifting production to tree crops, altering the methods of fertilizer application, matching nitrogen supply with demand, managing mineral nitrogen during fallow, applying less fertilizer more frequently during cropping, supplying fertilizer in irrigation water, using controlled-release fertilizers, using nitrogen-transformation fertilizers, and managing waste more efficiently. Most of these practices would increase agricultural productivity as well as minimize the introduction of N₂O into the atmosphere.

Item #d98oct6

“Mitigating Agricultural Emissions of Methane,” A. R. Monsier (USDA/ARS, Fort Collins, CO, 80521) et al., Clim. Change 40 (1), 39-80 (1998).

Ruminant animals, flooded rice paddies, animal wastes, and biomass burning produce about one-third of global methane emissions. Mitigative measures include improving the nutrition of animals with cereal grains, introducing genetic improvements, employing bovine growth hormone, improving feed formulations, modifying rumen fermentation through biotechnological approaches, adopting manure-management and -treatment practices (e.g., covered lagoons and digesters), managing water and nutrients during rice production, selecting low-emission rice cultivars, adopting new rice-cultivation practices, increasing the productivity of agricultural lands, lengthening the rotation times of shifting agriculture, managing grasslands, incorporating crop residues into the soil, using crop residues for household fuel, and shifting production to tree crops.

Item #d98oct7

“Possibilities for Future Carbon Sequestration in Canadian Agriculture in Relation to Land Use Changes,” J. Dumanski (Centre for Land and Biological Resources, Research Branch, Agriculture and Agri-Food Canada, Ottawa, Ontario, K1A 0C6, Canada) et al.,Clim. Change 40 (1), 81-103 (1998).

Several strategies for increasing carbon sequestration in agricultural soils in various regions of Canada were assessed. The most effective options are reducing summer fallow, converting fallow areas to hay or continuous cereals, fertilizing to ensure the nutrient balance, and adopting soil-conservation measures. Increased sequestration could be achieved in all regions of Canada, but the greatest gains could be made in areas with Chernozemic soils. Up to 75% of the total agricultural CO₂ emissions in Canada could be sequestered, but only for a limited time.

Item #d98oct8

“Carbon Sequestration and Turnover in Semi Arid Savannas and Dry Forest,” H. Tiessen (College of Agriculture, University of Saskatchewan, Saskatoon, Canada, S7N SA8) et al.,Clim. Change 40 (1), 105-117 (1998).

About 40% of the land in northeast Brazil has near-climax vegetation, less than 10% is planted annually, and about 35% is subject to shifting cultivation of five-year duration with >20-year recovery. Vegetative litter is partly decomposed and partly eaten by animals, resulting in low soil carbon levels; and cultivation depletes about 50% of these already low levels. In western Africa, up to 70% of the land is under agricultural management that returns very little carbon to the soil. Overgrazing and intensive collection of fuel wood have further degraded the soil, and short fallow periods on agricultural lands have led to serious declines in soil carbon stocks. In both these regions, greater sequestration could be effected by increased crop production under suitable rotations, longer fallowing, improved animal husbandry, and limitation of biomass burning.

Item #d98oct9

“Carbon Dioxide Fluxes and Potential Mitigation in Agriculture and Forestry of Tropical and Subtropical China,” Li Zhong (Institute of Soil Science, Academia Sinica, Nanjing 210008, China), Zhao Qi-Guo,Clim. Change 40 (1), 119-133 (1998).

Of the tropical and subtropical areas in China, about 40% is forest, 20% is cropland, and 20% is wasteland. Increasing productivity, boosting carbon inputs to the soil, and converting wasteland to agricultural production could sequester an estimated additional 1.9 TgC/y, and conversion of wasteland to fuel wood plantations and current forestry practices could sequester >30 and 7 TgC/y, respectively.

Item #d98oct10

“Mitigation by Agriculture: An Overview,” K. Paustian (Natural Resource Ecology Laboratory, Colorado State University, Fort Collins, CO, 80523) et al.,Clim. Change 40 (1), 135-162 (1998).

CO₂ emissions could be substantially reduced by reducing the conversion of tropical lands to agriculture, and an important method of doing that is the improvement of the productivity and sustainability of existing lands under cultivation. It is estimated that better soil management, restoration of degraded lands, setting aside of surplus agricultural lands, and restoration of former wetlands could sequester up to 0.9 PgC/y. Reducing direct agricultural emissions would produce modest mitigation, but the possibility of offsetting fossil-fuel consumption with biofuels could produce substantial mitigation.