Management of Irrigated Agriculture to Increase Organic Carbon Storage in Soils

Abstract

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 × 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 × 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 × 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.