Method Developed to Measure Solute Movement in Soils

Newswise — Scientists from Aarhus University and Aalborg University in Denmark have developed a new method for measuring the movement of solutes in intact soil. Improving on the existing method, the new procedure can be used on intact, undisturbed soil and provides more confident estimates.

Movement, or diffusion, of solutes in soils is involved in many processes of agronomical, environmental and technical interest. These include nutrient uptake in plants, decomposition of organic matter, and leaching of radioactive or unstable materials through clay barriers. The traditional measurement methods were developed for repacked sieved soil and are not well-suited for measuring intact soil samples, since they require prior knowledge of the magnitude of diffusivity of the individual soil sample – something which is often not available for intact soil due to its heterogeneous nature. Preliminary results were presented at the annual meeting for Soil Science Society of America in November 2007, and the full work has now been reported in the July-August issue 2010 of Soil Science Society of America Journal, published by the Soil Science Society of America. The method is a further development of the classical half-cell method, where two samples, one with a chemical tracer and one without, are placed into the half cells and connected, after which the samples are sliced and analyzed. The new method adds a fiberglass filter between the samples to improve water flow between the samples, and uses two sets of diffusing tracers instead of one. Using two tracers allowed the researchers to employ a dynamic model in estimating solute movement rates. Thus, researchers avoid issues with the classic method, such as that diffusion cannot exceed certain limits, and prior knowledge of the magnitude of diffusivity is not required. This can provide a more reliable result when estimating the diffusivity in individual soil samples. “The new method will provide a more reliable alternative to the existing methods when measuring the diffusivity of intact soil samples,” said Mette Lægdsmand, who developed the new method and the model, along with fellow researchers Per Moldrup and Per Schjønning. Research is ongoing at Aarhus University where the new method is being used to investigate key factors controlling the solute movement in intact soil, including moisture content, soil-water matric potential, and the soil structure. Researchers are also using the new method to investigate at which how soil moisture and the diffusion of solutes controls microbial activity as related to the decomposition of soil organic matter and production of greenhouse gases. The project was funded by the Danish Council for Technology and Production Sciences.

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Soil Science Society of America Journal,, is a peer-reviewed international journal published six times a year by the Soil Science Society of America. Its contents focus on research relating to physics; chemistry; biology and biochemistry; fertility and plant nutrition; genesis, morphology, and classification; water management and conservation; forest, range, and wildland soils; nutrient management and soil and plant analysis; mineralogy; and wetland soils.

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