Impact of Application of Poultry Litter on Water Quality and Wood Production in Forest Lands Phase II

Eddie P. Millhollon, Anderson, Russell A., Kilpatrick, Ricky L., Rabb, James L.  |  4/3/2007 11:54:27 PM

Image of the research site in Bienville Parish. In the picture the markers indicating plot treatment are visible.

Here Cooperative Extension agent Ricky Kilpatrick measures tree diameter.

This is an image of one of the collectors used to gather runoff.

Forestry and poultry are the largest respective plant and animal industries in Louisiana. Forestry was a $3.2 billion industry in Louisiana in 2006, and poultry production contributed nearly $968 million to the state's economy. Approximately 2,000 poultry houses in Louisiana collectively produce 200,000 tons of poultry litter annually. Poultry litter has been traditionally applied to pasture land, a practice that has been beneficial and environmentally sound. However, as these pasture lands become nutrient saturated, the potential for nutrient runoff and contamination of nearby water bodies escalates. Most of Louisiana’s forestry and poultry industries are located in the northern part of the state in close proximity to each other. Forest land in Louisiana is typically nutrient deficient and routinely fertilized with both N and P. This, coupled with the rapid nutrient uptake of forests during their active growing period, makes forest lands an attractive alternative to pasture lands for disposal of poultry litter. However, water body impairment resulting from runoff of excess nutrients, especially nitrogen and phosphorous, is a major concern

The 1996 Water Quality Inventory Report listed harvesting/reforestation as contributing to nonpoint source pollution and causing water quality impairment in watersheds north of Alexandria. The primary pollutant generated from this practice is sediment runoff to waterways. One possible way to decrease sediment runoff from forest lands is to improve the physical characteristics of forest soil and to promote growth of trees and native vegetation. Research has shown that poultry litter can not only provide essential plant nutrients for such growth, but can also improve soil organic matter, thus increasing the cohesive properties of soil, making it physically less likely to erode. The improvements in growth of trees and native vegetation and soil physical characteristics should improve water quality by reducing nutrient and sediment loading to receiving waters from forested areas.

Nitrogen, particularly nitrate nitrogen, and phosphates in poultry waste pose potential threats to water quality of water bodies near poultry litter application sites. Results from Phase I of this project indicated that poultry litter can be used successfully in a forest situation to improve soil fertility, especially soils deficient in phosphorous, and improve growth of young trees. However, application of poultry litter to forest land did significantly increase phosphate content of runoff water, although these increases were still within an acceptable range. Limited data indicated no adverse effects on quality of ground water in response to poultry litter application. Results also indicated that application of poultry litter can significantly decrease soil loss from erosion.

The purpose of Phase II is to determine the effect of successive annual applications of poultry litter since 2000 on pine tree growth, growth of native vegetation, soil erodibility and runoff water quality in a 25- to 30-year-old pine forest. The information provided through this project will be beneficial to the poultry producers and forest land owners, the local Soil and Water Conservation Districts and the Natural Resource Conservation Service in making determinations in how they should utilize their poultry wastes most effectively. The results of the project will be incorporated into educational outreach activities and included as recommendations made to forest land owners and poultry producers in the watersheds of north central Louisiana.

Objectives

The primary goal of this project was to demonstrate the beneficial use of organic waste for forest production and improvement of the quality of water in Louisiana.

Specific objectives to be determined included:

1. Comparison of growth-rate response of pine trees to different application rates of poultry litter. This will determine the required application rate for maximum growth enhancement.

2. Quantify runoff nutrient, pathogenic and sediment loading from the 25- to 30-year-old tree plots where applications can occur annually. This loading data will help identify the application rate with the maximum benefit for water quality of the receiving stream.

3. Verify improvement in soil properties based on application rates for poultry litter. This is not critical in terms of determining application rates but will help promote the beneficial use of poultry litter.

4. Based on the study, determine the best management practices for application of poultry litter on forested lands within the watersheds of north central Louisiana and disseminate this information to forest land owners and poultry producers in the region.

Method

The project area was located in a pine plantation with 25- to 30-year-old trees. Approximately 0.25-acre sites or study plots were previously selected in Phase I of this project to receive different application rates of poultry litter with one in used as a control (no application). The location of this site was representative of forested areas in north central Louisiana. The experimental design used was a randomized complete block design with treatments randomly assigned within three replicated blocks. Within each plot, several dominant trees representing the overstory of the plot were randomly identified and tagged. Growth response of these tagged trees was monitored by measuring the diameter breast height (DBH) at approximately 4.5 feet from the soil surface. Eight-foot-by-eight-foot exclusion cages were placed in random locations within each plot to prevent animals from disturbing the native vegetation. Vegetation within these cages was harvested to determine treatment effects on biomass production.

The best management practices (litter application rates) evaluated in the project included 0, 2, 4, 6 and 8 tons per acre. The 0 ton/A rate was considered the standard practice for comparison purposes.

Surface runoff water samples were collected from the 25- to 30-year-old plantation plots and analyzed for nitrate, total nitrogen, phosphate, total phosphorous, total and fecal coliform, total suspended solids, pH and As.

Results

Results from this study to date indicate that poultry litter can be used successfully in forestry production to improve soil fertility, especially soils deficient in phosphorous, with acceptable impact on water quality. For reasons that are as yet unexplained, 4 tons of PL/A resulted in the greatest amount of nitrates, phosphates, total phosphorous and total nitrogen in runoff water. It is the fact that these levels were greater than those found in runoff from plots that received 6 and 8 tons of PL/A that is puzzling. It is possible that 6 and 8 tons of poultry litter stimulated understory growth that was more efficient in uptake of these nutrients, since increasing poultry litter application did result in changes in understory species, but this hypothesis was not tested. Because this project was conducted in a mature pine plantation 25 to 30 years old, it was not surprising that the growth responses observed were minimal. That is to be expected with trees that are at the end of their active growing period.

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