Submitted to: Agronomy for Sustainable Development
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/30/2010
Publication Date: 8/18/2010
Citation: Sigua, G.C. 2010. Sustainable cow-calf operations and water quality: A review. Agronomy for Sustainable Development. 30(3):631-648.
Interpretive Summary: Current pasture management including cattle rotation in terms of grazing days and current fertilizer (inorganic + manures + urine) application rates for bahiagrass pastures in subtropical regions of USA offer little potential for negatively impacting the environment. Properly managed livestock operations contribute negligible loads of total phosphorus (P) and nitrogen (N) to shallow groundwater and surface water. Overall, there was no buildup of soil total P and N in bahiagrass-based pasture. These observations may help to renew the focus on improving fertilizer efficiency in subtropical beef cattle systems, and maintaining a balance of P and/or N removed to P and/or N added to ensure healthy forage growth and minimize P or N runoff. Contrary to early perception, forage-based animal production systems with grazing are not likely one of the major sources of non-point source P pollution that are contributing to the degradation of water quality in lakes, reservoirs, rivers, and ground water aquifers, but perennially grass-covered pastures are associated with a number of environmental benefits. Effective use and cycling of N or P is critical for pasture productivity and environmental stability. In addition to speeding up N or P recycling from the grass, grazing animals also can increase N or P losses in the system by increasing leaching potential due to concentrating N into small volumes of soil under dung and urine patches, redistributing N or P around the landscape, and removal of N or P in the form of animal products. The overall goal efforts to reduce N or P losses from animal-based agriculture should be to balance off-farm P inputs in feed and fertilizer with outputs to the environment. Source and transport control strategies can provide the basis to increase N and P efficiency in agricultural systems.
Technical Abstract: As animal agriculture has evolved to larger production operations in subtropical regions of United States, the problems associated with manure handling, storage and disposal have grown significantly. Understanding the interaction effects of sustainable cow farming with water-table management, nutrient dynamics and water quality in pastures could be the key to reducing nutrients in runoff. Soils do not contribute equally to nutrient export from watersheds or have the same potential to transport nutrient to runoff nor would soil test levels accurately predict total dissolved nutrients. Better understanding of soil nutrient dynamics and crop nutrient changes resulting from different management systems should allow us to predict potential impact on adjacent surface waters. In many states, these issues are critical and of increasing importance among environmentalists, ranchers, and public officials particularly in the case of nitrogen (N) and phosphorus (P). One of the first steps in assessing N or P level on any farm is to consider total N or total P inputs and outputs. In Florida, reduction of P transport to receiving water bodies is the primary focus of several studies because P has been found to be the limiting nutrient for eutrophication in many aquatic systems. Long-term monitoring of the changes in soil nutrients, especially soil P would enable us to predict soil chemical or physical deterioration under continuous forage-livestock cultivation and to adopt measures to correct them before they actually happen. Despite substantial measurements using both laboratory and field techniques, little is known about the spatial and temporal variability of nutrient dynamics across the entire landscape, especially in agricultural landscapes with cow-calf operations.