Irrigation Increases Inorganic Carbon in Agricultural Soils

Abstract

/ Inorganic C reactions are among the most important chemical reactions that occur in irrigated soils and may contribute to the total amount of C sequestered in those soils. Because CO2 can escape from soils to the atmosphere or return to precipitate carbonate minerals, soils are open systems with regard to inorganic C. We measured inorganic and organic C stored in southern Idaho soils having long-term land-use histories that supported native sagebrush vegetation (NSB), irrigated moldboard plowed crops (IMP), irrigated conservation (chisel) tilled crops (ICT), and irrigated pasture systems (IP). Inorganic C and total C (inorganic + organic C) in soil decreased in the order IMP>ICT>IP>NSB. We use our findings to estimate that amount of possible inorganic and total C sequestration if irrigated agriculture were expanded by 10%. If irrigated agricultural land were expanded by 10% worldwide and NSB were converted to IMP, a possible 1.60 x 108 Mg inorganic C (2.78% of the total C emitted in the next 30 years) could be sequestered in soil. If irrigated agricultural land were expanded by 10% worldwide and NSB were converted to ICT, a possible 1.10 x 109 Mg inorganic C (1.87% of the total C emitted in the next 30 years) could be sequestered in soil. If irrigated agricultural land were expanded worldwide and NSB were converted to IP, a possible gain of 2.6 x 108 Mg inorganic C (0.04% of the total C emitted in the next 30 years) could be sequestered in soils. Inorganic C sequestered from land-use changes have little potential to make a significant impact on the concentration of atmospheric CO 2.However, when coupled with organic C and altering land use to produce crops on high-output irrigated agriculture while selected less productive rain-fed agricultural land was returned to temperate forest or native grassland, there could be reductions in atmospheric CO2 .In 1992, nearly all countries of the world signed the Framework Convention on Climate Change. The longterm goal of this legislation is to stabilize the concentration of greenhouse gases in the atmosphere at concentrations that prevent interference with the climate system. To stabilize or reduce CO2 concentrations, emissions of the gas must either be reduced or transferred from the atmosphere to marine or terrestrial ecosystems. Irrigating arid and semiarid regions may be one method to contribute to C sequestration and, ultimately, reduce atmospheric CO 2 concentrations. The addition of water to arid and semiarid soils increases plant growth and, ultimately, C deposition into soil. Entry and others (2002) found that if irrigated agriculture were expanded by 10% into irrigated pastures, a potential increase of 9.3 X 109 Mg organic C (16.3% of

Effects of sandy desertified land rehabilitation on soil carbon sequestration and aggregation in an arid region in China

“…Irrigation and fertility management can increase SOC thereby accelerating formation of secondary carbonates in arid and semiarid soils through the addition of carbonic and organic acids that can react with soil silicates (Schwartzman et al, 1994). A greater increase of SIC content in irrigated cropland agrees with the results of Entry et al (2004) and Wu et al (2008), who reported that irrigation significantly increased inorganic carbon in agricultural soils of arid and semi-arid regions. Whitbread et al (1998) reported that labile C increased faster and more responsive than total soil C to changing management practices in the short-term.…”

Carbon management in dryland agricultural systems. A review

“…While Entry et al (2004) and Wu et al (2009) reported a greater amount of soil inorganic carbon in irrigated treatments compared with native soils, Denef et al (2008) did not find significant difference in soil inorganic carbon between irrigated and dryland treatments. In turn, Halvorson and Schlegel (2012) found that under limited irrigation, soil inorganic carbon tends to increase with time in all soil depths, supporting the results by Blanco-Canqui et al (2010).…”

“…Carbon sequestration as inorganic forms has been proposed as a viable alternative in irrigated soils in semiarid and arid regions (Entry et al 2004). However, the literature on this issue is scarce and also with contrasting arguments and results.…”

Soil organic and inorganic carbon and stable carbon isotopes in the Yanqi Basin of northwestern China

“…As the largest carbon pool in the terrestrial ecosystem, soil organic carbon (SOC) has attracted much attention. Soil inorganic carbon (SIC), existing mainly in arid and semi‐arid regions, may also play an important role in carbon sequestration and climate mitigation (Entry et al , ; Lal, ).…”