Traditionally, poultry litter has been spread as a fertilizer on pastures located in the 34 poultry-producing counties in Mississippi.
But a combination of long-term land application of poultry litter and decreases in pastureland has made this valuable byproduct too much of a good thing. The nutrient storage capacity of the soil in these south Mississippi counties has been pushed close to its limits, raising concerns of potential environmental problems from nutrient runoff into water sources.
Now, researchers are involved in a collaboration between the Mississippi Agricultural and Forestry Experiment Station and the Southwest Mississippi Resource Conservation and Development Council, Inc. They are investigating new uses for poultry litter that will ensure continued environmentally sound use of this material. The work could also expand the market for poultry litter.
One application being explored is use of poultry litter as a fertilizer in forests. Alex Friend, Mississippi State University forestry scientist and a member of the MAFES-RC&D project, has been studying the growth response of pine trees to poultry litter and the environmental quality issues associated with litter use in forests. His initial results from a noncommercial-scale study suggest raw poultry litter provides a good growth response in pine trees, but it has a minimal impact on water quality.
"Mississippi is heavily forested with pine trees growing in nutrient-deficient soils," Friend said. "We saw poultry litter use in forests as an opportunity to solve poultry litter disposal questions and solve nutrient deficiency in trees at the same time."
At the Coastal Plain Branch Experiment Station in Newton, Friend led a team that tested the effectiveness of stockpiled cake -- the top layer of raw poultry litter that has been cleaned out of a chicken house and stored -- as a one-time fertilizer in a thinned stand of 10-year-old pines.
In March 2000, they applied raw poultry litter at three application rates -- 0, 2.5 and 10 tons of litter per acre -- to the stand and then assessed growth by measuring tree diameter monthly.
"We were very surprised to see a growth response in trees within the space of six months," Friend said. "This is very unusual in forests because trees have so much mass and are buffered to changes. We think this shows litter has much potential for forestry use."
But another consideration that Friend had to make in his studies before reaching any conclusions was whether forests can "contain" the nutrients found in poultry litter. To answer this question, Friend's team placed PVC tubes 20 inches into the ground and collected soil water samples from just below the main tree root mat.
"Part of the paradigm we were testing was that existing trees in the stand would act as nutrient pumps to suck nutrients out of soil and prevent nutrient movement into water and the environment," Friend said. "We took lysimeter, or soil water, samples to give us an idea of what leaches through most of the tree roots and used it as an indication of what might make it to surface water."
As part of this study, his team collected soil water samples every month for more than a year.
"Within a month, we saw evidence of elevated nutrient availability in soil," Friend said. "But the significant thing with this part of the study was that application rates of 0 and 2.5 tons of litter per acre were usually indistinguishable in terms of nutrient leakiness into soil water. So this suggests a good growth response in forests can be obtained without adding so much poultry litter that nutrients run off."
Friend said he hopes to conduct a larger scale study that will look into more detail at the actual impact of poultry litter application in forests on a watershed.
While Friend has seen encouraging results with litter, he cautions that not everyone in the state may want to use poultry litter on forestland.
"Trees, and especially pine trees, are evolved to grow under low-nutrient conditions," Friend explained. "Results with poultry litter can be both good and bad, depending on soil conditions."
Friend also noted that his studies were based on using a single application of poultry litter in the lifetime of a tree stand. He said more work would be required to address the sustainability of this practice on a single piece of land. Still, Friend said he thought a significant acreage of Mississippi land could benefit.
"Poultry litter could be quite effective as fertilizer for landowners who have a mixed holding of poultry and forestland, or who live in proximity to poultry operations and are looking to improve tree growth in nutrient-deficient forests," he said.
Research data for this project are still being collected. Friend said he expects final results and recommendations for use to be available to landowners early next year.