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Atmospheric CO2 Enrichment Reduces Water Repellency of Soil
Newton, P.C.D., Carran, R.A. and Lawrence, E.J.  2003.  Reduced water repellency of a grassland soil under elevated atmospheric CO2Global Change Biology 10: 1-4.

What was done
In a FACE study conducted on the North Island of New Zealand, the authors measured the water repellency of a grassland soil after five years of photoperiod exposure to an extra ~100 ppm of CO2.  The pasture contained about 20 species of plants, including legumes, C3 grasses, C4 grasses and forbs, and was grazed periodically by adult sheep.

What was learned
There was a significant reduction in the water repellency of the soil in the elevated CO2 treatment when evaluated under normal field conditions.  In fact, the authors say that "at field moisture content the repellence of the ambient [treatment] soil was severe and significantly greater than that of the elevated [CO2] soil."

What it means
"Water repellency," as described by Newton et al., "is a soil property that prevents free water from entering the pores of dry soil (Tillman et al., 1989)," and they report that it "has become recognized as a widespread problem, occurring under a range of vegetation and soil types (agricultural, forestry and amenity; sand, loam, clay, peat and volcanic) (Bachmann et al., 2001) and over a large geographical range (Europe, USA, Asia, Oceania) (Bauters et al., 1998)."  Specifically, they note that water-repellency-induced problems for land managers include "increased losses of pesticides and fertilizers, reduced effectiveness of irrigation, increased rates of erosion, and increased runoff," and they report that there are water-repellency-induced problems "in the establishment and growth of crops (Bond, 1972; Crabtree and Gilkes, 1999) and implications for the dynamics of natural ecosystems, particularly those subject to fire (DeBano, 2000)."  Hence, it is clear that the CO2-induced reduction of soil water repellency discovered in this study portends a wide range of very important benefits for both agro- and natural ecosystems as the air's CO2 content continues to rise in the years and decades ahead.

Bachmann, J., Horton, R. and van der Ploeg, R.R.  2001.  Isothermal and non-isothermal evaporation from four sandy soils of different water repellency.  Soil Science Society of America Journal 65: 1599-1607.

Bauters, T.W.J., DiCarlo, D.A. Steenhuis, T.S. and Parlange, J.-Y.  1998.  Preferential flow in water-repellent soils.  Soil Science Society of America Journal 62: 1185-1190.

Bond, R.D.  1972.  Germination and yield of barley when grown in a water-repellent sand.  Agronomy Journal 64: 402-403.

Crabtree, W.L. and Gilkes, R.J.  1999.  Improved pasture establishment and production on water-repellent soils.  Agronomy Journal 91: 467-470.

DeBano, L.F.  2000.  The role of fire and soil heating on water repellency in wildland environments: a review.  Journal of Hydrology 231-232: 195-206.

Tilman, R.W., Scotter, D.R., Wallis, M.G. et al.  1989.  Water-repellency and its measurement by using intrinsic sorptivity.  Australian Journal of Soil Research 27: 637-644.

Reviewed 10 March 2004