PHOSPHORUS BALANCE MODEL TO PREDICT LAND BASE REQUIREMENTS FOR SUSTAINABLE ANIMAL FEEDING OPERATIONS

Authors: Sauer, Thomas; VANDEVENDER, KARL - ARK. COOP. EXT. SERV.; MAXWELL, CHARLES - UNIVERSITY OF ARKANSAS; DANIELS, MICHAEL - ARK. COOP. EXT. SERV.; Sharpley, Andrew; WATKINS, SUSAN - ARK. COOP. EXT. SERV.; Hatfield, Jerry; WEST, CHARLES - UNIVERSITY OF ARKANSAS; COFFEY, KENNETH - UNIVERSITY OF ARKANSAS

Submitted to: Meeting Abstract
Publication Type: Proceedings
Publication Acceptance Date: 10/11/2000
Publication Date: N/A
Citation: N/A

Interpretive Summary: Animal production facilities are decreasing in number but increasing in size. There is concern that it will be difficult for the very large facilities to utilize the manure generated in a way that is not damaging to the environment. One way to prevent this from happening is to estimate how much land is needed to accept all the manure from a facility. A model was developed that estimates how much phosphorus an animal production facility generates and, based on the cropping system, how much phosphorus is removed by the crop or lost in surface runoff. The difference between phosphorus input and removal was assumed to be the amount of phosphorus stored in the soil. The model estimated that a typical poultry operation in the Ozarks would bring about a rapid increase in the amount of phosphorus in the soil, reaching a maximum allowable soil phosphorus level in approximately 15 years. The model is now being modified for use with other animal manures and crop systems. The model is intended to be used as a management or planning tool by government agencies or individual growers interested in assuring that their land base is sufficient for the amount of manure generated.

Technical Abstract: Recent state and federal guidelines regarding land application of animal manures have included defining threshold soil test phosphorus (STP) levels above which further manure application is reduced or prohibited. The objective of this research project is to develop a model, called PTrend, for predicting STP trends in fields receiving animal manures. The PTrend model is designed to be used as a planning and management tool for identifying the land base necessary to assimilate phosphorus from confined animal feeding operations (CAFOs) while maintaining STP values below threshold levels. PTrend estimates STP using a P balance between the inputs from animal manure applications and losses through crop uptake and surface runoff. Simulations completed for a broiler/beef operation in the Ozark Highlands (8 broiler houses on 65 ha permanent pasture land base) indicated that the 336 kg/ha (300 lbs/A) STP threshold could be reached in approximately 15 years. Options simulated for reducing STP buildup included the use of phytase enzyme in the broiler diet to reduce excreted phosphorus and offsite forage removal by selling hay. These options were shown to be effective in slowing the increase in STP, but the density of animal production was still key to the long-term sustainability of the CAFO. Continuing efforts focus on expanding PTrend to consider row crop systems and other types of animal manures and to verify manure P availability estimates.