Management of irrigated agriculture to increase carbon storage

Authors: Sojka, Robert; ENTRY, J - PARK SERVICE; SHEWMAKER, G - UNIVERSITY OF IDAHO; FUHRMANN, J - UNIVERSITY OF DELAWARE

Submitted to: Proceedings of the New Zealand Lime and Fertilizer Institute Workshop
Publication Type: Proceedings
Publication Acceptance Date: 2/8/2007
Publication Date: 7/1/2007
Citation: Sojka, R.E., Entry, J.A., Shewmaker, G.E., Fuhrmann, J.A. 2007. Management of irrigated agriculture to increase carbon storage. In: Currie, L.D., Yates, L.J., editors. Proceedings of the Fertilizer & Lime Research Centre Workshop. Designing Sustainable Farms: Critical Aspects of Soil and Water Management, February 8-9, 2007, Palmerston North, New Zealand. p. 189-202.

Interpretive Summary: Irrigation is important to world food supplies, producing a third of the world’s crop yield on one sixth of its crop land and accounting for nearly half the value of agricultural crops produced. In addition, irrigation, which is predominately in arid and semi-arid settings, modifies the environment allowing an enormous increase in vegetative and root biomass production. After harvest there is a sufficient increase in biomass left on and in the soil, compared to annual native vegetative production, to eventually raise the equilibrium amount of soil organic carbon. Thus irrigation can raise the carbon sequestered in arid and semiarid soils to levels above natural baselines. This is potentially a substantial benefit for reducing carbon dioxide in the earth’s atmosphere, and thus for combating global warming. In addition to the effects of irrigation on soil organic matter, a small additional amount of carbon may be sequestered from the irrigation water as inorganic carbon from dissolved carbonates. Finally, recent studies have also shown a significant “direct” cooling effect from irrigation’s evapotranspirative service. This direct cooling can be as much as 8 degrees centigrade in proximity to irrigated areas and as much as 1 degree centigrade on a regional basis. This paper makes a strong case for re-examining public policy and incentives to support irrigation’s role in combating global warming.

Technical Abstract: Fossil fuel burning at the present rate, will double atmospheric carbon dioxide in this century, raising air temperature 1.5 to 5 degrees C. Sequestering carbon (C) in soil can reduce atmospheric carbon dioxide concentration. We measured inorganic and organic C in southern Idaho soils having long term land use histories of native sagebrush vegetation (NSB), irrigated moldboard plowed crops (IMP), irrigated conservation- (chisel) tilled crops (ICT) and irrigated pasture systems (IP). Soil Organic C (SOC) decreased in the order IP>ICT>NSB>IMP. We used our findings to estimate potential amounts of organic C sequestered if irrigated agriculture expanded. If irrigated agricultural land was expanded by10% worldwide and NSB was converted to ICT, 2.5 x 10^9 Mg organic C (4.38 % of the total C emitted in the next 30 yr) could potentially be sequestered in soil. If irrigated agricultural land were expanded by 10% worldwide and NSB were converted to IP, a possible 9.3 x 10^9 Mg organic C (16.32 % of the total C emitted in the next 30 yr) could be sequestered in soil. Irrigated agriculture produces twice the yield compared to non-irrigated land. Irrigation increases soil C relative to native semi arid or arid sites. Since irrigated agriculture produces higher yields, less land area needs to be put into production compared to rainfed agriculture. Altering land use to produce crops on high output irrigated agriculture, while returning less-productive rainfed agricultural land to temperate forest or native grassland, could further reduce atmospheric carbon dioxide. Inorganic carbon increases with irrigation were less consistent and much smaller than SOC. Irrigating these soils also increased microbial biomass and changed microbial diversity.