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Managing Nutrients in the Environment for Improved Soil and Water Quality

Congress: 2008
Author(s): Toor Gurpal

Keyword(s): water quality, animal farming, phosphorus, surface runoff, leaching
AbstractLand application of animal manures is a cost-effective alternative to beneficially recycle manures. However, long-term application of manures containing high amounts of nutrients such as phosphorus (P) has resulted in saturation of the soil with P. The greater accumulation of P in soils can lead to increased transfer of P to ground and surface water. The greater P losses to fresh waters from P-saturated soils are of environmental and ecological concern as they can lead to decreased water quality, including algal blooms, fish kills and loss of biodiversity, and can pose a threat to human health. In response to water quality deterioration in many water bodies, many states in the U.S. are now developing and adopting nutrient management strategies, which require the implementation of P-based management practices for manure and fertilizers when soils exceed state- defined upper limits of soil test P. Adopting P-based nutrient management plans will result in restrictions on manure applications and will limit the expansion of animal operations. Managing P inputs and outputs in animal farms to achieve “zero whole-farm P balance” should be the primary goal to reduce the costs of animal farming and to minimize the adverse impacts on environmental quality while complying with the federal and states’ rules and guidelines. Environmentally sustainable animal farms should have accurate accounting of P inputs both from feed and fertilizer, and means to recycle or export manure P for other uses such as composting, energy generation, pelletization, and granulation. Reducing the risk of P loss to surface and ground water is a complex and difficult task. Two of the more relevant approaches to improve P management and thus water quality are (i) Improved risk assessment protocols for P loss: Identification of soils where the risk of P loss by leaching is the greatest and reducing or eliminating inputs of P in fertilizers and manures to these soils, and (ii) Modification of animal diets to reduce manure P: In watersheds, where animal production is a vital component of the economy and alternatives to land application of manure do not exist or are limited, strategies to reduce the P concentrations in manures are critical for the future of animal agriculture. Dietary modification i.e., the use of dietary additives (e.g., phytase enzymes) and low phytic acid feed such as corn and soybean, and reductions in over-feeding of P have been shown to decrease P concentrations in manures by 20 to 50%. This reduces the P loading in soils, which in turn, decreases the risk of P loss to surface and ground water from manure-amended soils. This presentation will show case studies that demonstrate how linking P compounds in animal diets and manures can be instrumental in our efforts to optimize P use efficiency and improve soil and water quality. The scope of optimal management of P in continuum from diets- manures-soil-water will also be discussed.
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