Science emphasized at phosphorous symposium


(Editor’s note: Laurie Adelhardt, who lives in Berlin, Md.., is public relations coordinator for the Maryland Grain Producers Association. MGPA was a principal sponsor of the phosphorous symposium.)

WYE MILLS, Md. (Feb. 10, 2015) — More than 300 people from the agricultural, environmental and research communities came together at Chesapeake College in to learn about phosphorous and its role in Mid-Atlantic land and water resources at “The State of the Science on Phosphorous.”
Hosted by the Maryland Grain Producers Utilization Board, Chesapeake Bay Foundation and University of Maryland Extension, the symposium featured experts on the science of phosphorous from across the country who presented the current research surrounding phosphorous transport, soil dynamics, legacies, modeling and its impacts on water quality.
The Green Pastures and Blue Waters Paradox – Dr. Sharpley: Opening the program was Dr. Andrew Sharpley, a global leader in phosphorus science, from the USDA Agriculture Research Service in Arkansas. “Phosphorus is not an issue, it’s a resource,” said Sharpley.
Phosphorus (P) and nitrogen (N) are required for plant growth.
The public has grown to expect blue waters and green pastures, as well as an abundant supply of healthy and affordable food.
With predicted population growth, an increase in crop yields of 50-100 percent will be required, however, cheap, bountiful food can equate to environmental challenges.
The increased food demand will increase pressure to intensify and maximize yields, likely on less suitable lands.
Research on the sources and pathways of P loss has occurred for decades.
Conservation methods are based on the best science of the time, but still have a downside and drawbacks; nutrient management practices needs to evolve as advances in science occur.
To a large extent, concerns are fueled by a public debate of the wise use of conservation funding, an underlying desire for “quick fixes,” and an underestimation of the legacies of prior P and N management.
“This is not just a Chesapeake Bay issue, nor a new issue; the same phosphorus related issues were discussed fifteen years ago,” said Sharpley. “Future measures must manage for phosphorus and nitrogen and move towards targeted conservation systems. Developing partnerships with the science, environmental and farming communities, transferring the science to the farm to recover, recycle & reuse phosphorus, and managing expectations of stakeholders are key to the future.”
Impact of Phosphorus on Water Quality – Dr. Boynton: “Restoration trends have been observed in both small and large Chesapeake Bay systems, a very good sign,” said Dr. Walter Boynton, Professor at the Chesapeake Biological laboratory, University of Maryland Center for Environmental Science.
In the case of P in aquatic ecosystems, low dissolved oxygen conditions, elevated water pH and salinity all play a role enhancing phosphorus mobilization from sediments at the bottom of the Bay, essentially legacy P. Field and laboratory studies and simulation modeling all indicate rapid P responses to changing environmental conditions and a longer “system memory” for phosphorus than for nitrogen. It has been observed that the Bay is resilient and can respond quickly to a decrease in phosphorus load.
Both P and N play powerful roles in Bay water and habitat quality. Substantial reductions of N and P result in improved water quality and better habitat conditions. The pathways estuaries follow during degradation and restoration often involve time delays and abrupt threshold changes. Other factors are still to be understood through ongoing research.
Dr. Boynton encouraged stakeholders to stay with the basic model of nutrient enrichment and restoration which is solid and showing positive results. The dual nutrient reduction strategy is sound.
“Most people think nitrogen and phosphorus are pollutants; they are not. They are the stuff of life. We just have too much of a good thing,” Dr. Boynton.
Agricultural Phosphorus Sources – Dr. Kleinman: “There is no room in reasonable science for extreme hyperbole,” stated Dr. Peter Kleinman, a soil scientist with USDA-ARS and the research leader of the Pasture Systems and Watershed Management Research Unit in Pennsylvania.
The uncoupling of the production systems has exacerbated regional and local P accumulation.
Food production systems need to recycle P in a more efficient manner.
In addition, fertilizer recommendations are generally based on older data and analyses, therefore, new transparent, fertilizer recommendation systems that leverage old and new data need to be developed.
Erosion control is the first step to address soil P. Soil conservation is a priority, recognizing trade-offs with dissolved P, as P from the soil surface contributes to surface and subsurface flows. Vertical stratification must be addressed.
“Agronomic recommendations are not always based in science and need modernization; the basis of data is old,” said Kleinman.
The 4 “R”s of Nutrient Stewardship - applying the Right Source, at the Right Rate, at the Right Time, in the Right Place — are the basis for sustainable manure management to optimize production while minimizing environmental impact.
There needs to be an understanding of the trade-offs with conservation practices, as some practices can have unintended consequences.
For example, cover crops take up a significant amount of phosphorus with plant growth, but can also be a source of dissolved P after freeze/thaw cycling.
Hydrology of Phosphorus – Dr. Buda: Dr. Anthony Buda, a hydrologist with the Pennsylvania USDA-ARS Pasture Systems and Watershed Management Research Unit, reviewed the role of hydrological connectivity in P losses from representative agricultural landscapes across the Bay watershed.
Case studies ranged from upland basins dominated by variable source area hydrology to the Coastal Plain where artificial drainage is of primary concern, emphasized that this is not just a Chesapeake Bay issue. Hydrologically active areas drive P transport in sloped upland landscapes of the Bay watershed.
In the lowlands, artificial drainage increases the connectivity between P sources and receiving waters.
P transport in streams and rivers is event driven, with the majority of P loss occurring in a few large storms. Changes in the frequency of extreme events represent an area of emergent concern for P loss risk.
“Conowingo Dam is one of our huge legacy P sources, a large contributor of nitrogen and phosphorus to the Bay,” stated Buda. “None of our management systems are perfectly optimized, and both agronomists and environmentalists oversell their benefits.”
Computer Models for Phosphorus Management – Dr. Vadas: Goals in phosphorus (P) management include identifying major non-point sources and transport pathways, quantifying the amount of P lost from these processes, and developing realistically implementable practices to reduce P loss to environmentally sustainable amounts.
Because physical monitoring of agricultural systems to achieve these goals is expensive and time consuming, especially at large watershed scales, computer simulation models and decision-making tools are increasingly used to generate the information used to develop policies and practices.
“Model developers have the responsibility of communicating how the model works and that the data is science-based,” stated presenter Dr. Peter Vadas, soil scientist with USDA-Agricultural Research Service at the Dairy Forage Research Center in Madison, Wis. “To retain confidence in a model, modelers need to improve communication about what data they need. It is a quick and simple process to update model with new data.”
The Chesapeake Bay Model uses a process-based approach were equations are simple but physically-based.
It is semi-distributed, with 309 county-based land-segments from which P loads are determined and fed into 1063 watershed-based river-segments. Model variables are adjusted (calibrated) so simulated P loads reasonably match observed loads from monitoring.
The strength of the model is in understanding and simulating effect of P sources (soil P, manure, fertilizer) and transport (runoff, erosion) on P loss. Challenges of the model include predicting quantities and spatial simulation of runoff and erosion; drainage and related P transport (preferential flow); transport through stream networks; reducing complexity while maintaining robustness (watershed scale); and uncertainty.
Legacy Phosphorus – Dr. Smith: “Legacy phosphorus is anything in excess of terrestrial needs, not just excess crop needs,” Dr. Doug Smith is a soil scientist with USDA-ARS at the Grassland, Soil and Water Research Laboratory in Texas. “Legacy phosphorus is found throughout the landscape, it is not just agricultural land.”
Historically, diversified farming systems promoted on-farm phosphorus (P) balance, as the crops grown onsite fed the animals which generated the manure to fertilize the crops.
Modern agricultural systems have diverged from this simplistic system in the last 50-60 years such that P is mined in one region of the country, shipped to where the grain is grown, which is then shipped to where animal feeding operations are located.
With this shift in agricultural systems came inefficiencies that led to excess P within the agricultural landscapes. Agricultural conservation efforts have reduced many of these inefficiencies; however, the actions of the past have led to legacy P primed throughout the catchment.
From excessive soil P, to groundwater with high levels of P and long residence times, to P saturated ditch and river sediments, legacy phosphorus within a catchment is a source in slow but perpetual motion from the original site of application to the downstream receiving water bodies and can hinder current methods to remediate water quality issues. Smith stated that the Conowingo Dam is at about 90 percent of its sediment holding capacity, adding “that’s a lot of legacy P.”
“Legacy P will take decades to move through the system,” stated Smith. “We need an arsenal, not a single silver bullet.”
Agricultural Best Management Practices – Dr. McGrath: “The largest phosphorus loss pathway from a field is a crop removing it during the growth cycle,” stated Dr. Josh McGrath.
McGrath was an Associate Professor and Extension Specialist at University of Maryland and was heavily involved in Chesapeake Bay water quality issues and policy development prior to accepting a position in the Department of Plant and Soil Sciences, at the University of Kentucky in 2014.
Considerable investment in policies and practices to reduce agricultural P loading have been made in Maryland, with much of the discussion focused on local P imbalances and ways to increase P use efficiency.
Improving agricultural P recovery efficiencies might help avoid future legacy P losses that result from elevated soil P concentrations.
However, meeting short term water quality objectives will require a more holistic approach that aims to interrupt the field to water transport continuum by targeting P management practices and conservation measures to site-specific P sources and transport conditions.
“More resource allocation and more ag innovation are needed to develop more effective policy,” continued McGrath. “There is a difference between an agronomically significant loss and an environmentally significant loss. It’s time to use performance based metrics to choose BMPs. That’s the tradeoff with conservation.”
The long-term goal is to manage soil P. Best management practices based on today’s science address near-term goals. Scientists need to improve the transfer of research to farmers.
At the field level, the focus is to manage applied sources to minimize exposure and maximize crop availability.
Opportunities to interrupt transport pathways are the best approach to remediate P given the degree of legacy P in the entire watershed.
Ultimately BMPs are temporary actions to address a long-term, complex, systemic issue.
McGrath also mentioned that the research on the Phosphorus Management Tool will be published soon and there are differences between the published tool equations and those which were used in the regulation.
Implementation of Agricultural Phosphorus Management Policies – Dr. Coale: Dr. Frank J. Coale, Professor and Extension Specialist in the Department of Environmental Science & Technology at the University of Maryland, walked through a timeline of state nutrient management policies. Beginning in 1998, agricultural nutrient management efforts in Maryland embarked on a transformation from voluntary conservation practices to mandatory regulations.
“Science comes in small steps. We need to assess, readjust and move forward with the science we have to address nutrient management and phosphorus challenges,” stated Coale.
The program concluded with a question and answer session with all presenters. Proceedings of the symposium have been made available, with a recording of presentations to follow. An active conversation flowed throughout the day on Twitter, hashtag #P15Science.
“Phosphorus is a necessary nutrient for plants to grow,” concluded host Paul Spies, MGPUB President. “We hope attendees left with a better understanding of how phosphorus works, so together we can develop science-based answers to manage the nutrient effectively for food production with minimal environmental impact.”