Phosphorus Dynamics and Management in Forage Systems with Cow-Calf Operation

Abstract

Phosphorus fertilization is a vital component of productive farming. Phosphorus is an essential macronutrient that is required to meet global food requirements and make crop and livestock production profitable. While adequate levels of phosphorus in the soil are essential to grow crops, phosphorus has the potential to induce eutrophication in our water systems. Controlling phosphorus inputs is the thus considered the key to reducing eutrophication and managing ecological integrity. Forage-based cow-calf operations may have detrimental impacts on the chemical status of groundwater and streams and consequently on the ecological and environmental status of surrounding ecosystems. Relatively, little information exists regarding possible magnitudes of phosphorus losses from grazed pastures. Whether or not phosphorus losses from grazed pastures are significantly greater than background losses and how these losses are affected by soil, forage management, or stocking density are not well understood. The goal of this paper is to demonstrate the various effects of differing pasture fertility, animal behavior, and grazing management systems on the levels and changes of soil P in subtropical beef cattle pastures that will improve our understanding of P dynamics, cycling, and management in the agroecosystem. From our Florida experience perspectives, the following critical results are worthwhile mentioning: (1) environmentally, soil phosphorus in Florida pastures are declining; (2) soil phosphorus in pasture fields with no phosphorus fertilization were consistently lower than those of the fertilized fields by about 49.1 % to 40.9 % from 1988 to 2000, respectively; (3) soil phosphorus concentrations in 1988 of about 94.1 mg kg⁻¹ and in 2000 of about 69.2 mg kg⁻¹ were not high enough to be of environmental concern, so annual additions of phosphorus-fertilizer would be still practical to sustain plant and animal productivity in subtropical beef cattle pastures; (4) congregation zones in pastures with beef cattle operations in three regions of Florida are not phosphorus-rich, therefore may not contribute more phosphorus to surface and groundwater supply; and (5) slope aspect and slope position could be of relative importance in controlling spatial distribution of soil phosphorus. Effective use and cycling of phosphorus therefore is critical for pasture productivity and environmental stability in subtropics. This will help to renew the focus on improving inorganic fertilizer efficiency in subtropical beef cattle systems, and maintaining a balance of phosphorus removed to phosphorus added to ensure healthy forage growth and minimize phosphorus runoff. Additionally, if the overall goal is to reduce phosphorus losses from animal-based agriculture then there is a crucial need to balance off-farm phosphorus inputs in feed and fertilizer with outputs to the environment. Consequently, this paper has provided fundamental information on the source and transport control strategies that can provide the basis to increase phosphorus efficiency in agroecosystem with cow-calf operation.