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Inputs of P are essential for profitable crop and livestock production. However, its export in watershed runoff can accelerate the eutrophication of receiving fresh waters. The specialization of crop and livestock farming has created regional imbalances in P inputs in feed and fertilizer and output in farm produce. In many areas, soil P exceeds crop needs and has enriched surface runoff with P. This paper provides a brief overview of P management strategies to maintain agricultural production and protect water quality that were discussed at the conference, “Practical and Innovative Measures for the Control of Agricultural Phosphorus Losses to Water,” sponsored by the Organization for Economic Cooperation and Development and held in Antrim, Northern Ireland, June 1998. The purpose of the conference was to assess current strategies for reducing the loads and concentrations of P from agricultural land to surface waters. Topics discussed at the interdisciplinary conference and reviewed here included sustainable P management in productive agriculture; assessing land application of P; evaluating and modeling P transport and transformations in soil, runoff, streams, and lakes; and implementation of integrated best management practices (BMPs). From these discussions, measures to control agricultural P transfer from soil to water may be brought about by optimizing fertilizer P use‐efficiency, refining animal feed rations, using feed additives to increase P absorption by the animal, moving manure from surplus to deficit areas, and targeting conservation practices, such as reduced tillage, buffer strips, and cover crops, to critical areas of P export from a watershed.

Society relies heavily on inorganic phosphorus (P) compounds throughout its food chain. This dependency is not only very inefficient and increasingly costly but is depleting finite global reserves of rock phosphate. It has also left a legacy of P accumulation in soils, sediments and wastes that is leaking into our surface waters and contributing to widespread eutrophication. We argue for a new, more precise but more challenging paradigm in P fertilizer management that seeks to develop more sustainable food chains that maintain P availability to crops and livestock but with reduced amounts of imported mineral P and improved soil function. This new strategy requires greater public awareness of the environmental consequences of dietary choice, better understanding of soil-plant-animal P dynamics, increased recovery of both used P and unutilized legacy soil P, and new innovative technologies to improve fertilizer P recovery. In combination, they are expected to deliver significant economic, environmental, and resource-protection gains, and contribute to future global P stewardship.

Th is commentary examines an "inconvenient truth" that phosphorus (P)-based nutrient mitigation, long regarded as the key tool in eutrophication management, in many cases has not yet yielded the desired reductions in water quality and nuisance algal growth in rivers and their associated downstream ecosystems. We examine why the water quality and aquatic ecology have not recovered, in some case aft er two decades or more of reduced P inputs, including (i) legacies of past land-use management, (ii) decoupling of algal growth responses to river P loading in eutrophically impaired rivers; and (iii) recovery trajectories, which may be nonlinear and characterized by thresholds and alternative stable states. It is possible that baselines have shift ed and that some disturbed river environments may never return to predisturbance conditions or may require P reductions below those that originally triggered ecological degradation. We discuss the practical implications of setting P-based nutrient criteria to protect and improve river water quality and ecology, drawing on a case study from the Red River Basin in the United States. We conclude that the challenges facing nutrient management and eutrophication control bear the hallmarks of "postnormal" science, where uncertainties are large, management intervention is urgently required, and decision stakes are high. We argue a case for a more holistic approach to eutrophication management that includes more sophisticated regime-based nutrient criteria and considers other nutrient and pollutant controls and river restoration (e.g., physical habitat and functional food web interactions) to promote more resilient water quality and ecosystem functioning along the land-freshwater continuum.