November 2010, Vol. 22, No.11

Research Notes

Measuring solutes in soil

Scientists at Aarhus University (Denmark) and Aalborg University (Denmark) have developed a new method to measure solute diffusion in soils. Tracking solutes in soil can help determine nutrient uptake in plants, decomposition of organic matter, and leaching of radioactive or unstable materials through clay barriers, according to a Soil Science Society of America (Madison, Wis.) news release.

The research, reported in the July–August 2010 issue of Soil Science Society of America Journal, expands on traditional methods by enabling measurement of intact, undisturbed soil. Traditional methods, designed to measure sifted soil that has been repacked, rely on knowing the soil sample’s magnitude of diffusivity, which is information often not known about intact soil samples because of its heterogeneous nature, the news release says.

Both the new and traditional methods start with two samples, one with and one without a chemical tracer. The samples are placed into half cells and connected. With the new method, a fiberglass filter is inserted between the samples to improve water flow, and two sets of diffusing tracers are used. Researchers then slice and analyze the samples.

By using two tracers, the researcher no longer has to ensure that diffusion did not exceed certain limits and no longer has to have prior knowledge of the magnitude of diffusivity. The new method is expected to provide a more reliable result when estimating diffusivity in individual intact soil samples, because researchers can avoid the limitations of the traditional method.

The Danish Council for Independent Research, Technology, and Production Sciences, a part of the Danish Agency for Science, Technology, and Innovation (Copenhagen), funded the research on the new method.

Using the new method, researchers are investigating factors controlling solute movement in intact soil, including moisture content, soil-water matrix potential, and soil structure. They also are investigating at which moisture-content ranges the diffusion of solutes controls aerobic microbial activity related to decomposition of soil organic matter and production of greenhouse gases, the news release says.

Machine inserts poultry litter below soil surface

A new U.S. Agricultural Research Service (ARS) invention enables farmers to use waste products to boost crop production while reducing nutrient runoff and ammonia emissions. The Poultry Litter Subsurfer, invented by ARS soil scientist Dan Pote, injects dry poultry litter and composted cattle manure below the soil surface in pastures and no-till fields.

A research coalition led by U.S. Department of Agriculture scientist Peter Kleinman is testing prototypes of the machine. The research coalition spans five states in the Chesapeake Bay watershed: Delaware, Maryland, Virginia, Pennsylvania, and New York. It includes Kleinman and his research partners at Pennsylvania State University (University Park) and Virginia Polytechnic Institute and State University (Blacksburg). The coalition received a $786,000 Chesapeake Stewardship Fund grant to test four Subsurfer prototypes.

Pote led the collaborative project to develop the Subsurfer while another team, led by ARS agricultural engineer Tom Way, focused on developing a different prototype with adjustable row spacing for litter application in row-crop systems and pastures. Because of the different delivery systems for each machine, Pote and Way pursued different patents for the systems. Way’s invention has been patented, the news release says.

The tractor-drawn Subsurfer uses an auger system that crushes litter and distributes it to soil trenches, enabling precise control and low application rates, which previously was not feasible, the news release says. The machine causes minimal soil disturbance and can be used by no-till farmers who do not clear fields of crop residue before planting a new crop. The Subsurfer carries up to 4.5 Mg (5 ton) of litter and simultaneously opens eight trenches. Each trench is 51 mm (2 in.) wide, 76 mm (3 in.) deep, and spaced 305 mm (1 ft) apart, the news release says.

Studies show that the Subsurfer reduces nutrient runoff and ammonia emissions while increasing forage yields. Tests on Arkansas pastures by Pote showed increasing yields, with at least 90% reduction in runoff and emissions. Similar results were found by other ARS researchers and colleagues in Maryland and Pennsylvania.

With no machines on the market that can perform this task, ARS is applying for U.S. and international patents on the Subsurfer, and one company has applied for a license to commercialize it, the news release says.


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