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Concerns over Leaching from Stored Poultry Litter

by 5m Editor
3 September 2009, at 9:15a.m.

DELAWARE, US - The storage of poultry litter on field margins has become a cause for concern due to leaching of nutrients.

Nutrients leach out of the huge piles of poultry litter stored in farm fields over the winter, reports Cape Gazette. University of Delaware research is showing just how many pounds of nutrients run off those piles - and that covering them does not reduce run-off.

Temporary field storage of poultry litter in fields is a common practice across Delmarva.

Greg Binford, associate professor and extension specialist with the university, said growers have argued it is impractical to cover the stacks because the covers need to be replaced several times over the winter, and because condensation inside plastic wrap leaves a sticky mess that is hard to handle.

Dr Binford and other university researchers decided to test whether polyurethane covers were useful, and just how much nitrogen the piles deposit in soil. They conducted field tests over several years, beginning in 2005, as part of the university study.

The article explains that, using stainless steel pans and plastic storage bins inside the piles, the scientists measured run-off.

They also took soil samples from underneath the piles, as well as from along their edges and the surrounding area. They took measurements at intervals over the winters.

Dr Binford found, from a pile of 100 tons of litter, an average of 16 pounds of nitrogen leached out. Compared to 55 pounds of nitrogen per ton of litter, he said, that was not a very big amount. Data showed that more potassium leached out of the litter than any of the other nutrients tested for, about 10 times more than nitrogen.

Some piles were uncovered, while others were covered with sheets of polyurethane. Some were covered with various spray-on materials designed to keep water from running through, said Dr Binford. The spray materials ended up cracking and letting water in, which made the litter wet and difficult to use. Sections of the material fell off the piles.

The research was presented at a meeting of the Science and Technical Advisory Committee to the Center for the Inland Bays on 21 August, according to Cape Gazette.

Dr Binford said that when it rains, a top layer of the pile gets wet, but the inside would stay dry. In mounds that were pushed higher, there was a smaller wet layer because the water would run off more quickly, he said.

He added that the scientists noticed an even swath of plant growth around the edges of the piles, regardless of whether they were covered.

"Basically, what we found is none of them made a difference," Dr Binford said of the various types of covers, noting that in some piles covered with sheets of poly, there was even more nutrient release. Nutrient releases from the piles were all about the same, he said.

"All the spray-on covers provided no benefit and were sometimes worse," he added.

Compared to other methods of handling litter, including spreading it, properly stacked piles have less potential for nutrient loss, said Dr Binford.

Bill Moyer, committee member, asked Dr Binford how much less nutrient material is released from poultry litter stored in sheds. Dr Binford said less would be released. Before Mr Moyer's question, he said the sheds are designed for storage of the top layer of wet material taken out of chicken houses between flocks. The litter stacked in fields is drier, about 25 per cent moisture, and is from complete clean-outs of poultry houses.

In fields that were planted with no-till methods, Dr Binford said the patch where the litter was stored would stay barren because of the high concentration of nutrients. However, where farmers plowed the fields and mixed up the nutrients with the soils, plants would grow, he said.

Dr Binford said when this research began, there was no information on nutrient losses from large poultry-litter piles, and the previous studies were conducted on smaller piles, which was not an accurate test.

The Cape Gazette report explains that Delaware regulations allow uncovered poultry litter to be stacked up to six feet to be kept in a field for 90 days, said Binford. Stacks 10 feet tall can be kept up to 150 days, and all piles must be conical. He said the litter must be 100 feet away from surface water and 200 feet from wells.