James L. Rabb, Eddie P. Millhollon, W. David Caldwell and Jose Liscano
Poultry production is Louisiana’s largest animal industry and is concentrated in the Coastal Plains area in north central Louisiana. Poultry litter is a byproduct of poultry production, with an estimated 180,000 tons produced in 2000. Most of this litter has historically been applied close to poultry houses on land often used for hay or pasture production. Application of litter to the same land for many years has increased levels of phosphorus and other nutrients in the soils and has caused concern that surface runoff into adjacent water bodies could degrade water quality and cause algal blooms that ultimately deplete the oxygen supply, resulting in fish kills.
Poultry litter is a combination of manure and bedding material, and the nutrient content depends on the type of bedding material and nutrient levels of the feed for broilers. The average nutrient content of a ton of poultry litter is about 50 pounds each of nitrogen and phosphorus and 40 pounds of potassium. The nutrient content is quite variable, however, ranging from 34 to 90 pounds of nitrogen, 32 to 66 pounds of phosphorus and 16 to 48 pounds of potassium per ton of litter.
Cotton responds well to the application of nitrogen, as well as other nutrients, which makes poultry litter an attractive source of nutrients. In addition, soils that have long been in cotton production are often low in organic matter, and the application of poultry litter may increase organic matter as well as nutrients for cotton production. Although the nutrient content and soil amendment qualities make it attractive for row crop production, responsible management is an environmental challenge.
Another possible source of soil amendment for growing cotton is the solid waste matter produced by municipalities. Disposal of this solid waste has been a growing concern. Much is disposed of in landfills, but this is inefficient and costly. Although the nutrient content of municipal solid waste is relatively low, it may have a place in agricultural production as a way to improve pH, soil structure and organic matter.
Concern has been expressed that municipal solid waste contains high amounts of heavy metals. However, most are removed before it enters the waste stream. Bossier City, La., produces “Enviro soil,” which contains about 0.6 percent nitrogen (N), 0.5 percent potassium (K), 0.75 percent phosphorus (P) and 27 percent calcium as well as smaller amounts of other nutrients. Heavy metals are present, but well within the U.S. Environmental Protection Agency’s level of tolerances. The major nutrient content (N, P, K) is much lower than that of poultry litter and the calcium content is very high, especially for the cotton-producing soils of Northwest Louisiana that have near neutral to slightly alkaline pH values.
Hairy vetch is an ideal legume cover crop for cotton production. Cover crop research at the LSU AgCenter Red River Research Station over a 40-year span has shown that cotton following hairy vetch will produce yields that equal or exceed conventionally applied nitrogen. An added benefit of using hairy vetch is that it will increase or maintain organic matter, resulting in improved water-holding capacity of the soil.
A three-year field experiment was conducted on a Norwood very fine sandy loam soil at the Red River Research Station to compare the response of cotton to poultry litter, municipal solid waste (from the Bossier City treatment facility), hairy vetch and sidedress nitrogen. Two tons per acre of poultry litter and municipal solid waste were applied, and, along with hairy vetch, incorporated before planting. Beds were formed and planted with either Paymaster 1218 BG/RR (1997) or SureGrow 125BR (1999, 2000) cotton. Nitrogen (32 percent solution) treatments of 0, 35 and 70 pounds nitrogen per acre were applied in split plots as a sidedressing four to six weeks after plant emergence. LSU AgCenter recommended cultural practices were followed.
There were no significant interactions between nitrogen rate and poultry litter, municipal solid waste or hairy vetch. Average seed cotton yields were highest for poultry litter regardless of additional nitrogen application (Figure 1). Seed cotton produced with two tons per acre of poultry litter without additional nitrogen exceeded that of the recommended 70 pounds of nitrogen per acre. A sidedressing of 35 and 70 pounds of nitrogen to poultry litter plots did not significantly affect yield. Cotton grown following a hairy vetch cover crop yielded somewhat less than when following poultry litter, but exceeded yields of all nitrogen rates without amendments. Cotton yield following hairy vetch was not affected by the application of additional nitrogen in this study. Municipal solid waste applied at two tons per acre provided a slight increase when compared with nitrogen only.
Soils in the cotton-producing areas of the Red River Valley are characteristically low in organic matter. Improvement in organic matter is one of the benefits of cover crops and soil amendments. The effect of the soil amendments on nutrient composition of the soil is unknown. Table 1 contains soil data following four years of annual applications of poultry litter, municipal solid waste and winter growth of a hairy vetch cover crop on the same plots. Although continuous nitrogen plots contained only 0.86 percent organic matter, the plots receiving four annual applications of poultry litter contained 1.19 percent organic matter, followed by hairy vetch with 1.02 percent. Municipal solid waste plots contained only 0.89 percent.
Organic Matter Increases Yields
Although the increase in organic matter is small, research at the Red River Research Station has documented a significant increase in cotton yields from a small increase in organic matter. The increase in soil phosphorus following the use of poultry litter was higher than the other treatments; however, these levels are within acceptable limits. The calcium content of municipal solid waste is a concern in neutral to alkaline soils. Although not evident in this study, the increase in pH and calcium content of the soils following the application of municipal solid waste may cause nutrient problems for crops, including cotton. Levels of heavy metals from the use of organic wastes were not increased. Results from this study:
– Use of poultry litter as a soil amendment and hairy vetch as a cover crop increases cotton yield and soil organic matter.
– Two tons per acre of poultry litter produced yields equal to 70 pounds of nitrogen per acre.
– Adding sidedress nitrogen had little effect on cotton yield of poultry litter or vetch-treated plots.
– Organic matter increased approxi- mately 0.3 percent, which may have enhanced cotton yield and soil water-holding capacity.
– Increased yields and organic matter following hairy vetch were less than from poultry litter, but higher than from municipal solid waste or nitrogen alone.
– Municipal solid waste had no effect on organic matter content and did not significantly increase cotton yield.
– Use of the soil amendments did not adversely affect the level of heavy metals in the soil.
– The increase in pH and calcium content of the soil associated with municipal solid waste application may affect cotton yield adversely and should be monitored.
James L. Rabb, Professor; Eddie P. Millhollon, Associate Professor; W. David Caldwell, Professor; and Jose Liscano, Associate, Red River Research Station, Bossier City, La.
(This article appeared in the winter 2002 issue of Louisiana Agriculture.)