Table 1.

Synopsis of challenges and research needs identified by delegates at the 7th International Phosphorus Workshop, held in Uppsala, Sweden, September 2013

Theme	Challenges	Major research needs
1. P management in a changing world	Increasing P-use efficiency of diverse cropping systems, along with great water-use efficiency Fertilizers including mineral and organic sources Cost-effective recovery of P from manures and organic by-products and sludges Reconnecting spatially separated arable and livestock production systems	Crop breeding for increased P-use efficiency Development of 4R strategy to site-specific practices Unifying disparate policies to address P management and sustainability among countries Options for restructuring agriculture to the close P cycle
2. Transport pathways of P from soil to water	Magnitude and timescales over which P is retained and remobilized along transport pathways, and how this contributes to the accelerated storage of ‘legacy’ P within the landscape Quantifying subsurface water and P pathways and fluxes Evaluating processes and rates of P retention and recycling along transport pathways and up-scaling to the watershed Understanding long-term historical trajectories of legacy P accumulation and drawdown along transport pathways	Interfacing with digital terrain models, current GIS land use, soil surveys, and farmer knowledge of land response to identify drainage patterns Use of ‘background’ chemically inert tracers, already present in the environment, to evaluate hydrological pathways across watersheds Changing land use effects on P loss in surface and subsurface transport pathways Long-term monitoring of P loss pathways and fluxes along land–water continuum
3. Monitoring, modeling, and communication	P transport in subsurface drainage still poorly understood Model credibility can only be achieved with careful independent calibration, verification, and validation Models are increasingly used in policy decision-making, quickly providing maps and numbers at user low cost Monitoring is essential but costly Communicating model uncertainty and limitations to policy makers and public is the responsibility of the modeler	Monitoring programs must have clearly defined goals Long-term monitoring at various scales is essential All nutrient inputs and sources in catchments need to be represented Accurate models estimating P movement in artificial and preferential flow pathways Selection of the right model for the right scale and purpose Communication of model benefits and limitations is as important as predictions
4. The importance of manure and agricultural production systems for P management	Spatially disconnected intensive arable and livestock production systems exacerbate broken P cycle Vale of manure and other P-rich by-products inadequately recognized Development of cost-effective manure treatment and cost-beneficial by-products is currently limited Reduce urban waste generation, increase waste and by-product quality, and ensure recycling in agriculture	Plant genotype development and rhizosphere mgt. to stimulate P mobilization in low P soils Development of chemical and biological treatment that enhances fertilizer P value of generated by-products Assess possibilities of diversifying agricultural systems that sustain a closed P balance Overcoming the acceptability and biosecurity concerns of the public with using by-products as fertilizers
5. Identification of appropriate measures to decrease P losses	Edge-of-field P loss reductions brought about by conservation practices are highly site-specific High cost of conducting site-specific edge-of-field studies Disconnects between agricultural and limnological researchers limit cause and effect response development Still difficult to assign P levels in aquatic systems to current land use inputs or legacy inputs stored in soil and sediments	Innovative sampling and analytical technologies to make field assessment cheaper yet reliable at high sampling frequencies Development of amendments to sequester P in soil, manure, and by-products but retain plant availability Development of new cropping systems and rotations with great P-use efficiency, including catch crops
6. Implementation of measures to decrease P loss	Conservation measures can retain P on the land that will eventually become slow P release legacy sources Uncertainties of when and how much improvement in water quality will occur with restrictive land use of P Balancing the demand for cheap food with the desire for clean water Embracing the paradigm of adaptive system mgt. with stakeholder involvement, and flexible monitoring and policies Acceptance of green labels or sustainability metrics for environmentally sound-source food has been limited	Development of road map for equitable balance of restoring impaired waters with food security of increasing population that is more affluent Estimating the legacy of past land use and recovery pathways that are long and tortuous Given reversion to “pristine” conditions may not be possible, what aquatic environments are achievable and affordable? Targeting the right remedial measures at the right level to be cost-effective, with or without cost-sharing