Problem
It is generally assumed that dry soils are freely and uniformly moistened by rain and irrigation. However, in some soils a resistance against moistening is observed. Extremely water repellent or hydrophobic soils remain dry even after a wet season or after long periods of rainfall or irrigation.
Recent inventories indicated that water repellent soils are present in millions of hectares all over the world. These areas could often be delineated because of the influence of water repellency on agricultural production.
Water repellency has important effects:
- Peat can be water repellent after dehydration. Therefore, dikes consisting of peat are not quickly remoistened after a dry period. If the surface water levels rise, these dikes may breach because of the reduced mass of the dehydrated peat.
- Reduced infiltration capacity of the soil may cause a significant rise of surface runoff and erosion of slopes.
- Water may follow preferential flow paths in the soil, which implies that pesticides arrive early in ground water and surface water. Furthermore, since the soil is not uniformly moistened irrigation water is not effectively utilized.
- Water repellency causes reduced availability of water and nutrients for plants, which may result in strongly reduced crop yields.
Although water repellency has been subject of scientific research for a long time and with scientists from all over the world involved, up to now relatively little is known about the exact causes and characteristics. Besides this, little is known about the exact effects, and, more important, about effective methods to control water repellency. As a consequence, water repellency is currently controlled in a way which might be ineffective and harmful to the environment.
Research done by Alterra
Specialists of the Soil Centre co-operate with international colleagues in research on water repellency. During the last decade a tremendous progress has been made which resulted in enlightening insights into this complex matter. A vast amount of scientific papers has been published in international journals.
Applications
Alterra is currently involved in research on peat dikes in the province of Noord-Holland. Here some dikes breached during the summer of 2004 because of dehydrated and water repellent peat in the dikes. More specifically, Alterra investigates methods to remoisten the dehydrated peat in the dikes.
Alterra leads the Water Reuse project which focuses on reuse of remediated industrial waste water in NIS countries and Mediterranean countries. Important topics of interest are efficient, uniform moistening of soils and prevention for water repellency.
References
Websites
Water Reuse project website (2005-heden)
Water Repellent Soils project website (1998 -2001).
Publications
Dekker, L.W., Oostindie, K., Ritsema, C.J., 2000. Effects of surfactant treatments on the wettability of the surface layer and the wetting patterns in a water repellent dune sand with grass cover. Alterra Report 079, Wageningen, The Netherlands. 75 pp.
Dekker, L.W., Doerr, S.H., Oostindie, K., Ziogas, A.K., Ritsema, C.J., 2001. Water repellency and critical soil water content in a dune sand. Soil Sci. Soc. Am. J. 65, 1667-1674.
Doerr, S.H. and C.J. Ritsema (Editors). 2006. Special Issue “Soil Water Repellency: Origin, Environmental Controls and Hydrological Impacts”. Hydrological Processes, in press.
Doerr, S.H., R.A. Shakesby, L.W. Dekker and C.J. Ritsema. 2006. Occurrence, prediction and hydrological effects of water repellency amongst major soil and land use types under a humid temperate climate. Eur. J. of Soil Sci. 1-14.
Doerr, S.H., Dekker, L.W., Ritsema, C.J., Shakesby, R.A., Bryant, R., 2002. Water repellency of soils. The influence of ambient relative humidity. Soil Sci. Soc. Am. J. 66, 401-405.
Doerr, S.H. and C.J. Ritsema. 2005. Water movement in hydrophobic soils. In: Encyclopedia of Hydrological Sciences, Chapter 72, Wiley & Sons, U.K..
Kramers, G., J.C. van Dam, C.J. Ritsema, F. Stagnitto, K. Oostindie and L.W. Dekker. 2005. A new modeling approach to simulate preferential flow and transport in water repellent porous media: model sensitivity, and effects on crop growth and solute leaching. Austr. J. Soil Res. 43:371-382.
Ritsema, C.J., Dekker, L.W., editors. 2000. Water repellency in soils. Special issue Journal of Hydrology 231-232. 434 pp.
Ritsema, C.J., Dekker, L.W., 2000. Preferential flow in water repellent sandy soils: Principles and modeling implications. Journal of. Hydrology 231-232, 308-319.
Ritsema, C.J. (Editor) 2005. Special issue “Behaviour and Management of Water Repellent Soils’, Austr. J. Soil. Res. 43, 220 pp..
Ritsema, C.J., J.C. van Dam, K. Oostindie and L.W. Dekker. 2005. A new modeling approach to simulate preferential flow and transport in water repellent porous media: model structure, input, output and validation. Austr. J. Soil Res. 43:361-369.
Ritsema, C.J. and L.W. Dekker (Editors). 2003. `Soil water repellency: occurrence, consequences and amelioration’, Elsevier Science, Netherlands, 352 pp.
Ritsema, C.J. and L.W. Dekker. 2003. Modeling and implications of preferential flow in water repellent sandy soils. In: Ritsema, C.J. and L.W. Dekker (Eds.) Soil water repellency: occurrence, consequences and amelioration, Chapter 24, Elsevier Science, Netherlands, pp. 259-269.