Irrigation increases carbon in agricultural soils

Entry, James A. and Sojka, R.E. and Shewmaker, Glenn E. (2003) Irrigation increases carbon in agricultural soils. pp. 391-395. In: Proceedings 16th Triennial Conf. of ISTRO: Soil Management for Sustainability. Australia-Brisbane, 2003/07/13-18.

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Abstract

Irrigated agriculture sequesters significant amounts of organic C. Irrigation may also
sequester significant amounts of inorganic C. Inorganic C reactions are important chemical reactions
in irrigated soils and may contribute to the total amount of C sequestered. Calcium content of arid and
semi-arid soils tends to be higher than rainfed temperate soils due to calcium rich parent material and
low rainfall. Carbonate formation is usually controlled by carbonate equilibrium reactions in the solid
and g as phase CO2 . Respiration in plant roots and soil microorganisms continually produce CO,
increasing its concentration in the soil atmosphere, modifying carbonate solubility. Since irrigation
water flows through a series of canals, where smaller amounts of water are directly exposed to
incoming radiation, irrigation water usually has higher temperatures than stream or ground water.
Carbon dioxide dissolves in water to form both CO2 as a gas and H2CO3 in solution. Warmer water
increases reaction time and, in favourable conditions, precipitates CaCO3 .We measured organic and
inorganic C stored in southern Idaho soils having long term land use histories that supported native
sagebrush vegetation (NSB), irrigated mouldboard ploughed 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 the
amount of possible organic, 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 1.90 x 10' Mg total (organic +inorganic) C (2.72 % of the total C emitted in the next
30 yr) could be sequestered in soil. If irrigated agricultural lands were expanded by 10% worldwide
and NSB were converted to ICT, a possible 1.30 x 10' Mg total C (2.24 % of the total C emitted in the
next 30 yr) could be sequestered in soil. If irrigated agricultural land were expanded worldwide and
NSB were converted to IP a possible gain of 1.7 x 10 8 Mg total C (1.174 % of the total C emitted in
the next 30 yr) could be sequestered in soils. Altering land use to produce crops on high output
irrigated agriculture, while selected less-productive rainfed agricultural land were returned to
temperate forest or native grassland. there could be meaningful reductions in atmospheric CO 2 .

Item Type:	Conference or Workshop Item (Paper)
NWISRL Publication Number:	1123
Subjects:	Soil > Chemistry Mass Import - autoclassified (may be erroneous)
Depositing User:	Dan Stieneke
Date Deposited:	20 Nov 2010 21:56
Last Modified:	07 Nov 2016 16:45
Item ID:	942
URI:	https://eprints.nwisrl.ars.usda.gov/id/eprint/942