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DIVISION S-6—SOIL & WATER MANAGEMENT & CONSERVATION

Management of Irrigated Agriculture to Increase Organic Carbon Storage in Soils

^a USDA–ARS, Northwest Irrigation and Soils Research Lab., 3793 North, 3600 East, Kimberly, ID 83341
^b Univ. of Idaho, Research and Extension Center, Twin Falls, ID 83303-1827

* Corresponding author (jentry{at}nwisrl.ars.usda.gov)

Increasing the amount of C in soils may be one method to reduce the concentration of CO₂ in the atmosphere. We measured organic C stored in southern Idaho soils having long term cropping histories that supported native sagebrush vegetation (NSB), irrigated moldboard plowed crops (IMP), irrigated conservation-chisel-tilled crops (ICT), and irrigated pasture systems (IP). The CO₂ emitted as a result of fertilizer production, farm operations, and CO₂ lost via dissolved carbonate in irrigation water, over a 30-yr period, was included. Net organic C in ecosystems decreased in the order IP > ICT > NSB > IMP. In this study, if NSB were converted to IMP, 0.15 g C m^-2 would be emitted to the atmosphere, but if converted to IP 3.56 g C m^-2 could be sequestered. If IMP land were converted to ICT, 0.95 g C m^-2 could be sequestered in soil and if converted to IP 3.71 g C m^-2 could be sequestered. There are 2.6 x 10⁸ ha of land worldwide presently irrigated. If irrigated agriculture were expanded 10% and the same amount of rainfed land were converted back to native grassland, an increase of 3.4 x 10⁹ Mg C (5.9% of the total C emitted in the next 30 yr) could potentially be sequestered. The total projected release of CO₂ is 5.7 x 10¹⁰ Mg C worldwide during the next 30 yr. Converting rainfed agriculture back to native vegetation while modestly increasing areas in irrigated agriculture could have a significant impact on CO₂ atmospheric concentrations while maintaining or increasing food production.

Abbreviations: ICT, irrigated conservation-chisel-tilled crops • IMP, irrigated moldboard plowed crops • IP, irrigated pasture systems • NSB, native sagebrush vegetation

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