| [Image: Application of poultry litter.] |
| [Image: Overhead view of cotton with visible signs of nutrient value of poultry litter.] |
| [Image: Seed Cotton Yield (lbs./A)] |
Cotton production has been an important part of Louisiana agriculture for decades. Unfortunately, continued use of the same land over several years can result in a decline in important chemical and physical characteristics that were initially inherent to these soils before they were used for farming. Some of these deficiencies could potentially be corrected by supplementing these soils with organic material from Louisiana’s poultry industry. The poultry industry is Louisiana’s top animal industry with over 2,000 poultry houses distributed across the north central part of the state. Collectively, these houses produce over 200,000 tons of poultry litter annually. Traditionally, poultry litter has been applied to nearby pastureland -- a practice that has been beneficial and environmentally sound. However, the continued application of litter to the same pastures year after year eventually results in these soils becoming nutrient-saturated, thereby increasing the potential that excess nutrients will run off into nearby water bodies, possibly leading to eutrophication. There is therefore a need to identify alternative sites where litter can be applied as a needed nutrient source without adversely affecting the environment.
Litter produced by Louisiana’s poultry industry includes manure and bedding material. The nutrient content of the litter varies depending upon the type of bedding material and feed used for poultry production. Generally, though, each ton of poultry litter contains about 50 to 60 pounds of nitrogen (N), 50 pounds of phosphorus (P) and 40 pounds of potassium (K). The amount of nitrogen from litter that will become available for cotton growth depends upon several factors including soil pH, temperature and moisture. However, it is generally assumed that about 60 percent (30 to 36 pounds per ton) will become available. Therefore, at least two tons of litter are required to supply 60 pounds of nitrogen. Because Louisiana soils vary in P content and therefore may or may not need additional P, it is suggested that poultry litter be applied on a P-based instead of N-based basis and additional N supplemented if needed. This helps minimize the potential for surplus P to run off into nearby water bodies.
To determine the potential benefits from the use of poultry litter for cotton production in Louisiana and the environmental impact of this practice over time, a study was initiated in 1998 at the LSU AgCenter’s Red River Research Station near Bossier City, La. The study compared applications of poultry litter and inorganic fertilizer in conventional and conservation tillage systems. For purposes of this study, conventional tillage involved incorporating shredded cotton stalks, followed by deep tillage in the fall. Rows were bedded approximately three weeks before planting. The conservation tillage system involved delayed seedbed preparation and deep tillage following the shredding of cotton stalks in the fall, but crop residue and volunteer vegetation remained on the surface until the rows were bedded about three weeks before planting. The goal was to encourage native winter cover and maintain at least 30 percent ground cover from harvest until three weeks before planting.
The study was conducted on a Caplis very fine sandy loam soil. The site consisted of approximately eight acres that were precision sloped at 2 inches per 100 feet with laser land-grading equipment. Twelve-row plots (0.25 acre) were replicated four times. Treatments consisted of conventionally tilled and conservation plots that received either 60 pounds of nitrogen or two tons of poultry litter per acre, and a conservation plot that received four tons of poultry litter per acre.
Poultry litter was applied in the spring with a tractor-mounted spreader that was calibrated to apply a rate of two tons per acre. For this study, the two-ton rates were applied with a single pass and the four-ton rate with two passes. Analysis of the poultry litter indicated that the application of 2 tons per acre was equivalent to 71 pounds of nitrogen per acre, 35 pounds of phosphorous per acre and 56 pounds of potassium per acre. After litter application, all plots were disked to incorporate winter vegetation and litter and bedded to form 40-inch rows.
Cultural practices for cotton production recommended by the LSU AgCenter were followed. Plots that were fertilized received nitrogen (32 percent solution at 60 pounds of nitrogen per acre) placed in the top of the row with a knife applicator. Rows in all plots were shaped with a row conditioner to provide a seedbed uniformly raised to about 4 inches. A cotton variety recommended by the LSU AgCenter was planted at the rate of 10 pounds of seed per acre. A pre-emerge herbicide, a seed-protecting fungicide and an insecticide were applied at planting.
Poultry Litter Provides Yields Comparable to Inorganic Fertilizer
Comparing the various treatments for their influence on cotton yield (Figure 1) indicated no significant differences among the different treatments in 2008. Conventional tillage and 60 pounds of nitrogen per acre -- considered a standard practice for cotton production -- resulted in the lowest seed cotton and lint yield. All plots that received poultry litter as a soil supplement produced higher cotton yields than plots that received inorganic nitrogen fertilizer.
Results
This study demonstrates that poultry litter can be used effectively as a source of nutrients for cotton production in Louisiana with the added benefits of improvements in soil chemistry and organic matter. It also demonstrates the benefits of conservation tillage, particularly when poultry litter is used as a soil amendment.