Use of Poultry Litter as a Soil Amendment in Southern Row Crop Agriculture: A Feasibility Study Based on Agronomic, Environmental, and Economic Factors (AS93-10)
Poultry production in the U.S. is concentrated in the southeastern states. In this region, poultry are produced very efficiently by growing large numbers of birds in relatively small areas. However, this concentrated type of animal agriculture also results in the production of large quantities of poultry manure that must be disposed of in a way that does not harm the environment. This is becoming more and more difficult to do, because there is only so much land in the vicinity of the poultry houses on which to spread the manure, and levels of potential pollutants such as phosphorus are getting dangerously high in this land.
Poultry litter, a mixture of manure and a bedding material such as sawdust, could be a valuable fertilizer material for traditional southeastern row crops such as cotton, corn and soybeans, but the poultry producing areas are generally a long ways away from areas where row crops are grown. Despite this, it appeared that there might at least be some scenarios in which it would make economic sense to haul litter from the poultry producing areas, where it was rapidly becoming a problem, to millions of acres of soils used for row crop production.
The objective of our study was to assess the economic feasibility of transporting litter from poultry producing areas to row crop areas in two representative southeastern states, Arkansas and Alabama. To do this, it was necessary to study how row crops responded to litter applications on a variety of soils. It was also important to determine whether or not poultry litter could be applied to the soil in row crop areas in such a way that it would not be harmful to the environment.
1.) Quantify both the short-term and long-term agronomic value of poultry litter.
2.) Document the environmental consequences of land application of poultry litter in the row crop regions.
3.) Using the agronomic data on yield responses, estimate the farm level derived demand for poultry litter and poultry litter compost as a soil amendment; integrate the derived demands with costs of acquisition, transportation and application to determine the market feasibility of litter transport from areas of concentrated poultry production.
Our experiments consisted of applying two different forms of poultry litter, fresh and composted, to a variety of soils at several different rates, growing crops on the litter amended soils, and then measuring crop yields and selected soil and water parameters indicative of environmental quality. These data were then used to predict the scenarios in which litter could be economically transported from poultry producing areas to row crop areas. Crops grown in Arkansas were soybean and winter wheat. Some of the environmental indicator variables which were measured were nitrate leaching, soil pH and salinity, and floodwater concentrations of phosphorus and other elements (rice only).
The results of these experiments showed that, when applied on an equivalent nitrogen basis, poultry litter was as good a source of nitrogen as inorganic fertilizers such as urea or ammonium nitrate. From an agronomic point of view this means litter was usually as good as the commercial fertilizers.
An exception to this general rule was observed on plots that had lost much of their topsoil as a result of either erosion or land forming. On these soils, litter usually outperformed the commercial fertilizers. While we are not absolutely sure why this happened, it is consistent with the results of similar experiments by other researchers and is most likely due to the fact that poultry litter is a more complete fertilizer, i.e., it contains small but measurable amounts of many plant-essential nutrients in addition to significant quantities of nitrogen, phosphorus and potassium.
Litter seldom outperformed commercial fertilizers on plots that still had most of their original topsoil. The results also showed that there is little or no difference between the fertilizer value of fresh and composted litter. Spring applications of litter were shown to be more effective than applications the previous fall. Beneficial effects from a single, large, previous-year application were observed, but multi-year applications at lower rates produced greater yield of rice and cotton.
Impact of Results
Overall, there were no serious environmental consequences of applying litter to the row crop soils in our study. There were no indications of salt accumulation in soils receiving litter, nor were there any long-term changes in soil pH associated with use of litter. In the more poorly drained Arkansas soils, there was no evidence of nitrate leaching, but there was evidence of nitrate leaching from soil fertilized with high rates of litter in Alabama. This leaching could largely be controlled by planting a winter cover crop on these soils.
Not surprisingly, it was found that whether or not it was economically feasible to use poultry litter as a fertilizer in the row crop regions depended on several variables. The most important of these variables were cost of litter compared to commercial fertilizers, transportation costs, the magnitude of the difference between crop yields produced by litter application compared to commercial fertilizer application, and crop prices. The results of the economic analysis suggest that there is significant derived demand for poultry litter and poultry litter compost as soil amendments. The use of fresh poultry litter can be profitable for rice, cotton and soybeans in some years when litter can be obtained at a price of $45 per ton or less. Given the fact that fresh litter is generally available for $5 to $47 per ton in the poultry producing areas, a market should exist for locations where the total transportation costs are $40 per ton or less. In pairwise comparisons with fresh litter, the general trend observed was that, at a lower cost fresh litter outperformed the poultry litter compost.
The greatest potential market for both fresh and composted poultry litter appears to be as an amendment for degraded soils, particularly those whose productivity has been seriously impaired as a result of either erosion (more common in Alabama) or land forming (leveling) operations (more common in Arkansas). Application of poultry litter to degraded soils often resulted in significantly higher yield than those obtained through the application of inorganic fertilizers. The higher derived demand that this created for the litter would allow the litter to be used profitably even when its total price exceeded $45 per ton.