Future agriculture with minimized phosphorus losses to waters: Research needs and direction

Andrew N. Sharpley Lars Bergstrom Helena Aronsson Marianne Bechmann Carl H. Bolster Katarina Borling Faruk Djodjic Helen P. Jarvie Oscar F. Schoumans Christian Stamm Karin S. Tonderski Barbro Ulen Risto Uusitalo Paul J. A. Withers The series of papers in this issue of AMBIO represent technical presentations made at the 7th International Phosphorus Workshop (IPW7), held in September, 2013 in Uppsala, Sweden. At that meeting, the 150 delegates were involved in round table discussions on major, predetermined themes facing the management of agricultural phosphorus (P) for optimum production goals with minimal water quality impairment. The six themes were (1) P management in a changing world; (2) transport pathways of P from soil to water; (3) monitoring, modeling, and communication; (4) importance of manure and agricultural production systems for P management; (5) identification of appropriate mitigation measures for reduction of P loss; and (6) implementation of mitigation strategies to reduce P loss. This paper details the major challenges and research needs that were identified for each theme and identifies a future roadmap for catchment management that cost-effectively minimizes P loss from agricultural activities. - Phosphorus (P) impairment of surface waters remains a concern worldwide, such as in Asia (Wang 2006; Novotny et al. 2010; Dai et al. 2011; Sun et al. 2012; Li et al. 2015), Europe (Hilton et al. 2006; Withers and Jarvie 2008), South America (Shigaki et al. 2006), and USA (National Research Council 2008; Dubrovsky et al. 2010). Agriculture is a proven, but variable, contributor of P to many impaired waters (Sharpley et al. 2009; Ulen et al. 2010; Haygarth et al. 2012). Remedial strategies have been in place for 2030 years to address these impairments, for example, in the Chesapeake Bay Watershed (U.S. Environmental Protection Agency 2010a), Mississippi River Basin (Dale et al. 2010), Floridas inland and coastal waters (U.S. Environmental Protection Agency 2011), and Lake Erie Basin (Sharpley et al. 2012a). In many cases, however, water quality improvements have been less than expected for several reasons; these include but are not limited to legacy P inputs (i.e., P from prior land and nutrient management), climate fluctuations, ineffective conservation practices, and inadequate P management policies (Mulla et al. 2008; Meals et al. 2010; Sharpley et al. 2013; Jarvie et al. 2013a). This continued water quality impairment provided the critical backdrop to the 7th International Phosphorus Workshop (IPW7) held in Uppsala, Sweden in early September, 2013. Major goals of this conference were to discuss current research on P management in agricultural systems and water quality impacts and to identify major gaps and future research needs. The latter objective was addressed by discussion groups focused on six scientific area themes (Table 1), within which questions were identified by conference attendees prior to the conference. The six scientific themes are depicted in Fig. 1 and are interrelated in the sustainable management of global P resources. Delegates met throughout the conference, and insights were gained as the conference proceeded. This paper summarizes the discussions and research recommendations. The main challenge Improvements in agriculture in the last 50 years have dramatically increased grain and protein production in a very The Author(s) 2015. This article is published with open access at Springerlink.com www.kva.se/en 1. P management in Increasing P-use efficiency of diverse cropping systems, a changing world along with great water-use efficiency Challenges 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 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 Table 1 Synopsis of challenges and research needs identified by delegates at the 7th International Phosphorus Workshop, held in Uppsala, Sweden, September 2013 2. Transport pathways of P from soil to water 3. Monitoring, modeling, and communication 5. Identification of appropriate measures to decrease P losses Major research needs 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 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 Communication of model benefits and limitations is as important as predictions Plant genotype development and rhizosphere mgt. to stimulate P mobilization in low P soils Understanding long-term historical trajectories of legacy P accumulation and drawdown along transport pathways Evaluating processes and rates of P retention and recycling along transport pathways and up-scaling to the watershed Changing land use effects on P loss in surface and subsurface transport pathways Long-term monitoring of P loss pathways and fluxes along landwater continuum P transport in subsurface drainage still poorly understood Monitoring programs must have clearly defined goals 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 Long-term monitoring at various scales is essential Accurate models estimating P movement in artificial and preferential flow pathways Communicating model uncertainty and limitations to policy Selection of the right model for the right scale and purpose makers and public is the responsibility of the modeler Vale of manure and other P-rich by-products inadequately Development of chemical and biological treatment that recognized enhances fertilizer P value of generated by-products Development of cost-effective manure treatment and cost- Assess possibilities of diversifying agricultural systems that beneficial by-products is currently limited sustain a closed P balance Reduce urban waste generation, increase waste and by product quality, and ensure recycling in agriculture 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 Overcoming the acceptability and biosecurity concerns of the public with using by-products as fertilizers Innovative sampling and analytical technologies to make field assessment cheaper yet (...truncated)