John L. Kovar, Caye M. Drapcho, M.L. “Ron” Robbins and Don L. Robinson
Eutrophication. Pfisteria. Hypoxia. These environmental problems have plagued the Chesapeake Bay area in recent years. According to reports, the problems may be related to the excessive amounts of nutrients – especially phosphorus – that enter the watershed from areas of intensive poultry production surrounding the bay. Since Louisiana has an active and expanding poultry industry, do we face similar problems? If so, what is being done? If not, then what can be done to prevent such problems? A group of LSU Agricultural Center scientists is addressing these questions.
Poultry production in Louisiana generated $388 million in gross farm revenues in 1998, with nearly $325 million of the total attributed to broiler production. More than 811 million pounds of broilers were produced by 711 growers in 12 parishes. Union Parish led the state with 245 producers selling 305 million pounds of broilers. Based on projections by representatives of the processing companies – known as integrators – these figures will rise in 1999.
A typical farm consists of four poultry houses, each capable of producing five flocks per year, with an average of 20,000 birds per flock. With poultry production comes poultry litter. Litter is a combination of poultry manure and bedding material, such as rice hulls or pine shavings. Litter accumulates at approximately one ton per 1,000 birds. At this rate, it is not surprising that more than one million tons of litter were removed from poultry houses in Louisiana in 1998. Poultry litter nutrients
Poultry production is concentrated in hilly areas of the Coastal Plain dominated by pastures and forests. Grain shipped into these areas for feed is a significant source of nutrients, and these nutrients accumulate in poultry litter. Since most of the forests have dense undergrowth that prevents land application of the litter, the material is generally applied to nearby pastures. The land is usually accessible throughout the year and relatively close to the poultry houses. This practice has been a common means of disposal for more than 40 years in some areas.
The litter provides plant nutrients and organic matter to the soils – two components that have historically limited crop production in the highly weathered, low fertility soils of the Coastal Plain. It is important that this material be applied to the soil in a manner that makes the nutrients available to plants, yet minimizes nutrient losses that can adversely affect water quality. The potential for nutrient losses in runoff water is especially high where poultry litter is left on the soil surface of sloping land.
An application of poultry litter is not the same as an application of commercial fertilizer. Fertilizers applied to croplands are often mixtures of nitrogen, phosphate and potash (N, P2O5, K2O), which are balanced to meet the needs of the crop. Unfortunately, the nutrients in poultry litter are not balanced to meet the needs of the forages to which the litter is usually applied. The average sample of fresh poultry litter contains 60 pounds per ton of N, 55 pounds per ton of P2O5 and 30 pounds per ton of K2O, as well as lesser amounts of calcium, magnesium, copper and zinc. These values can vary significantly depending on the type of feed, age of the birds, manure management system and climate, so individual sources must be analyzed for nutrient content. Most litter contains approximately equal amounts of N and P2O5. Producers commonly apply sufficient litter to satisfy the nitrogen needs of the crop. Since forage crops need two to four times as much N as P2O5, phosphorus is overapplied and accumulates in the soil. This is especially true in fields from which a hay crop is not removed. In the past, this buildup of soil phosphorus has not been a concern. Phosphorus is relatively stable in soil; significant losses were thought to occur only by soil erosion.
Recent research has shown that significant amounts of soluble phosphorus can be present in runoff water from pastures with excessive soil phosphorus. This soluble phosphorus can negatively affect water quality in nearby lakes and streams. Phosphorus itself is not toxic, but it limits the growth of algae and aquatic plants in freshwater lakes and streams. Small increases in phosphorus concentrations can trigger algal blooms and unwanted vegetative growth, which lead to eutrophication and hypoxic conditions.
Phosphorus associated with litter applications to pastures is probably being lost from soils in Louisiana, although the extent of the problem is unknown. The status of soils, crops and water in Louisiana poultry-producing areas must be determined before best management practices can be developed to reduce the risk of nutrient losses. Searching for answers
In 1993, a survey was conducted in Union Parish to assess the effects of poultry litter applications on soil nutrient status and forage production at 25 locations. Soil samples were collected from pastures that had not received broiler litter and from pastures that had received unknown amounts for as long as 45 years. The level of available nutrients was very low in soils that had not received poultry litter. Nutrient levels generally increased as years of litter application increased, although the highest levels were found at a site that had received litter for 23 years (Table 1).
Soil phosphorus increased more than any other nutrient. After only four years of litter application, soil phosphorus averaged 134 parts per million; this is considered high for a Coastal Plain soil. After 10 years of litter application, soil phosphorus levels became excessive, thereby increasing the potential for losses in runoff water. The highest soil phosphorus was found at a site located on a footslope. Runoff water from the surrounding area probably was more important than the number of years of litter application in causing the high phosphorus levels. Less litter per acre of land was applied at the 40- to 45-year sites, so soil phosphorus levels were lower than at sites receiving litter for 22 to 23 years.
In addition to phosphorus, the concentrations of available copper and zinc also increased from very low levels to excessively high levels (Table 1). The effect of such high soil levels on the concentrations of copper and zinc in forage tissues is being evaluated. Soil nitrate-nitrogen levels were very low in the top 2 feet of soil, suggesting that applied N was used by the forages. Soil potassium, calcium and magnesium concentrations increased as years of application increased but did not reach excessive levels. Finally, organic matter content consistently increased with years of litter application (Table 1). Small increases in organic matter content can significantly improve soil structure, soil water-holding capacity and the ability of roots to absorb water and nutrients. Long-term plots
After the Union Parish study, longterm plots were established in 1995 at the Calhoun Research Station in Ouachita Parish to determine the effect of poultry litter applications on water quality, soil nutrient levels and growth of forage species and loblolly pine. Four rates of poultry litter were applied to the newly established forage plots and plots established in a stand of 10-year-old pine trees. Litter is reapplied each spring. Runoff samples are collected and processed after each rainfall. After only two applications of litter, preliminary data suggest that the amount of phosphorus in runoff water depends on application rate, length of time before the first rainfall after litter application and rainfall intensity. More important, nutrient and sediment loads in runoff from areas with pine trees are significantly lower than those from pastures. This strengthens the argument that poultry litter could benefit commercial timber lands without negatively affecting surface water quality.
To further investigate whether nutrients are actually being lost from lands that have received poultry litter, scientists from the LSU Agricultural Center have initiated several other studies of runoff from natural and simulated rainfall. In 1997, a study was initiated at the Hill Farm Research Station in Claiborne Parish to monitor both N and P in surface runoff from a bermudagrass pasture. Four rates of poultry litter are being compared to commercial fertilizer applied at recommended rates. Nutrient content of the soil and plant tissue also is monitored. In Union Parish, plots were established at four locations in 1997 to quantify the relationship between soil P content and the concentration of P in surface runoff. A rainfall simulator is being used to produce surface runoff. A second objective of the study is to evaluate the profile distribution and potential plant availability of P from previous poultry litter applications, which range from one year to 30 years, at the four sites. A more basic study is examining whether mobile colloids in these soils play a role in the transport of phosphorus into surface and groundwater.Alternative source
Other research addresses the use of poultry litter as an alternative nutrient source. The goal is to develop best management practices for various production systems. At this time, cotton, loblolly pine and a subclover/bahiagrass/ pine agroforestry system are being studied. The nutrient value of poultry litter is being compared with that of commercial fertilizer. Timing and rate of litter application, nutrient availability and nutrient removals are variables under consideration.
In addition to controlling application rates, several other solutions have been proposed to the problem of limiting the amount of P from poultry litter that finds its way into surface waters. Research in Arkansas has shown that treatment of poultry litter with aluminum sulfate (alum) before land application will tie up much of the added P in the soil. In this case, soluble P in surface runoff will not increase above background levels, thus preventing contamination of lakes and streams.
A more cost-effective solution to the problem may come from the integrators themselves. It is well known that much of the phosphorus in poultry litter could be eliminated by altering the feed rations of the birds. Poultry and other nonruminant animals cannot process organic forms of P in the digestive tract. Nevertheless, phosphates are required for proper skeletal growth, so digestible P is added to feed. As a result, the birds excrete large amounts of P. But, if a specific enzyme called phytase is added to feed, poultry can use organic phytate in the feed. With this additive, the amount of dietary P that must be added to feed can be reduced, which reduces the amount of P in the litter by 20 percent to 30 percent. A further reduction in the P content of litter can be achieved by using low-phytate corn in the feed rations of the birds. Several commercial seed companies are moving toward the development and release of low-phytate corn hybrids, which show great promise for producers in both the poultry and swine industries. Management required
Regardless of whether feed additives and litter treatments are used, poultry waste will always contain some phosphorus and other nutrients that require management. Moreover, soils in a number of pastures already contain phosphorus levels well in excess of forage crop demands. These sites will have to be intensively managed for several years to ensure that the P is not lost to surface waters. Excessive levels of soil phosphorus may require 15 to 20 years of continuous crop removal, Flowers without phosphorus additions from any source, before soil phosphorus decreases to agronomic levels.
Given the current national concern for contamination of surface and ground water from agricultural non-point sources, one thing is certain – nutrient management will become more important. At this time, the application of poultry litter is not regulated in Louisiana. This offers producers more options for handling excess nutrients. Restrictive regulations could cause financial hardship among producers and negatively affect the Louisiana economy. Hence, there is a need for additional research to help producers manage, use or market the nutrients in poultry litter to ensure that this valuable resource is used effectively to improve the fertility of Louisiana soils.
John L. Kovar, Associate Professor, Department of Agronomy
, LSU Agricultural Center, Baton Rouge, La.; Caye M. Drapcho, Assistant Professor, Department of Biological and Agricultural Engineering
, LSU Agricultural Center, Baton Rouge, La.; M.L. (Ron) Robbins, Resident Director and Professor, Calhoun Research Station
, Calhoun, La.; and Don L. Robinson, Resident Director and Professor, Texas Agricultural Experiment Station, Texas A&M University, Vernon, Texas.Acknowledgments
Personnel involved with poultry litter research include Donald J. Boquet, Gary A. Breitenbeck, J. Blair Buckley, Terry R. Clason, Darren R. Cooper, Marcus M. Eichhorn Jr., Terri L. Eiler, Eddie R. Funderburg, Charles J. Graham, Howard W. Gryder, Rodney Hendrick, Eddie P. Millhollon, David G. Morrison, James L. Rabb and P. Mark Walthall.(This article was published in the spring 1999 issue of Louisiana Agriculture.)