Download Agricultural Phosphorus and the Environment

Agricultural Phosphorus and the Environment:
Challenges for Science, Practice and Policy
Andrew Sharpley
Department of Crop, Soil and Environmental Sciences, University of Arkansas,
Fayetteville, Arkansas, USA.
While phosphorus (P) is essential input for profitable crop and livestock agriculture, its loss in runoff
accelerates eutrophication of receiving surface waters. Interest in minimizing P delivery has been
heightened by the recent findings that coastal eutrophication may be seasonally influenced by P as well
as N. Best Management Practices (BMPs) or “Codes of Good Practice” to mitigate P transfers to surface
water must address specific agronomic, environmental and socio-economic conditions. These practices
can be categorized as those that are related to the management of farm inputs, manures, and land use
selection. Innovative methods are becoming available to more closely balance farm inputs in feed and
fertilizers with grain and protein produced as greater costs are being associated with environmental
sustainability. Although manures are an on-farm nutrient resource, they often constitute a major source
of farm P surpluses and with a limited farm land base for proper utilization, lead to unacceptable P
enrichment of surface waters. “Manure BMPs” involve decreasing the solubility of P in manure with
chemical amendments or physical treatment, moving manure from surplus to deficit areas, and
development of alternative uses for manure other than land application. “Land-use BMPs” are designed
to limit runoff, erosion and leaching as important pathways of indirect and direct transfer of P to stream
and rivers. These include such practices as conservation tillage, terracing, and stream buffers. “Grazing
BMPs” aim to decrease the impact of grazing animals on in-stream export of P and include stream-bank
fencing, as well as more intensive pasture and grazing management. It crucial that further research on
BMPs involves tradeoffs between P and N as well as among surface runoff, leaching and gaseous loss
reduction efficiencies. We need to move from looking at one element or delivery pathway in isolation of
others.
Even though there has been a concerted effort to implement remedial measures through voluntary
and regulatory means, the long-term challenges of P surpluses at farm, watershed, and regional scales,
more research is neither the single nor the final solution. Many farmers simply do not have the financial
resources to implement and maintain costly remedial measures. Despite there being many cost-share
programs in the USA to help defray remedial costs, institutional red-tape and conflicting requirements
often limit program enrollment and hinder their widespread adoption and maintenance. In some
instances, local or regional governmental or agency controls may be necessary to enhance quicker
adoption of practices that will have a positive influence on environmental outcomes. A major shortcoming
of many remedial programs has been a lack of farmer education, showing that they have a role to play in
improving water quality many miles from their farm. In Arkansas, we are attempting to address these
challenges though development the Watershed Research and Education Center, where urban
development is rapidly moving into rural areas and replacing farms and pastures. The Center is at an
agricultural and urban interface and provides an unique opportunity to research, demonstrate and
educate on BMPs and urban development practices that can be used to reduce the delivery of storm
water and sediments, nutrients and other contaminants to streams. Public recreation activities are also
planned at the Center to show how they to have a role to play in mainlining clean water and more
importantly, how critical farming is and that sound environmental stewardship is being practiced.