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Phosphorus (P) is the second most limiting plant essential nutrient in global agriculture with no substitute, and at the same time a major contributor to negative water quality impacts. Plant available soil P in some soils of the world today is in excess while in other cases soils are severely deficient in P. Sustainable agricultural systems must find ways to manage P to avoid either of these cases.

In general, global agriculture today and in the foreseeable future is highly dependent on commercial sources of P manufactured from mined phosphate rock. These deposits are abundant but are not uniformly distributed among the major nations of the world. The USGS currently estimates phosphate mine reserve life to be over 300 years and phosphate rock resources to be much greater. Clearly, we are not on the verge of running out of P. However, approximately 75% of known global P rock reserves are located in Morocco and China with only 1% found in the US. Nations of the world will become increasingly interdependent as time passes for their agricultural systems to be sustainable, especially in the case of P. Market and policy factors will likely continue to add value to the recycling of P via the return of P from regions of consumption to regions where crops originally removed the P from soils.  

Much of the sustainability challenge for P is founded in its extreme global variability among nations, regions within nations, fields within regions, and zones within fields. The take-home message, whether you are a farmer, a researcher, an educator, a business leader, a non-profit, or a policy maker is to be cautious about using averages. The solution to the P challenge may often reside inside the average.

Over the last 50 years, phosphorus concentrations increased in many Missouri and Upper Mississippi River Basin water bodies, specifically, those in agricultural watersheds. During that same period, agricultural productivity doubled through agricultural intensification and adoption of new innovative technologies. Although efficiency of our agricultural systems has increased, water quality remains a concern. Identifying solutions to achieve nutrient reduction goals is challenging. This challenge is exacerbated by climate change. Watershed scale approaches incorporate ecosystem processes and consider how variations in landscape characteristics effect hydrologic processes, which may result in response lags from field to stream. Conservation implementation strategies must consider these complex interactions controlling nutrient loss, while also incorporating practical management options that prioritize regional agronomic goals. The success of any water quality program is dependent upon the availability of willing landowners to implement a conservation practice or adjust their nutrient management. Prioritizing land management that improves soil resilience across a watershed will not only benefit the farmers’ long-term productivity, it will sequester carbon, increase infiltration, decrease soil erosion, improve water holding capacity, and reduce overall phosphorus runoff and leachate.

Contributions of streambanks to total phosphorus (P) loads reaching downstream receiving water bodies are a growing concern within many watersheds. Only a few studies exist on near-stream and streambank soil chemistry and P concentrations, spatial distributions in watersheds, and P loading rates to streams. This presentation will discuss a series of research studies aimed at understanding the dynamics of P in near-stream riparian buffers, quantifying streambank P concentrations and variability within streambanks and across watersheds, and quantifying P loads from streambanks at the reach scale. Research results will be discussed from studies at numerous riparian floodplain and streambank sites in Oklahoma and North Carolina. Our research suggests that riparian buffers are highly capable of trapping upslope P before entering streams and rivers with the total P trapping efficiency dependent on the total runoff reduction and total sediment deposited within the riparian buffer (Fox and Penn, 2013). This high trapping efficiency can result in the saturation of near-surface soils with P capable of being released into streams as the result of streambank erosion and failure. Streambanks and upslope riparian buffers are uniquely susceptible to preferential flow due to the abundance of root channels, biological activity, and frequent wetting and drying cycles; this preferential flow can connect streambanks to upslope areas and circumvent the trapping efficiency of riparian buffers (Guertault et al., 2021). This leads to unique channel erosion rates and P transport dynamics. Watershed-specific variability in streambank erosion and streambank P concentrations should be expected. Longitudinal trends in streambank P concentrations are not always present. Streambank P contributions and erosion rates along one stream cannot be used to predict P loading along other streams even in similar watersheds with similar hydrology, geomorphology, and land use (Purvis et al., 2016). Such results suggest the need for even more quantification of streambank P concentrations and streambank erosion rates within watersheds of interest. Furthermore, short-term monitoring of streambank erosion rates may not capture the dynamics of streambank erosion and failure (Daly et al., 2015). Therefore, mechanistic models and uncertainty analysis approaches are needed to capture appropriately the uncertainty in critical input parameters for both the streambank erosion process and the expected streambank P loads for analyses at the reach scale (Fox et al., 2016).

References:

• Daly, E. R., Miller, R. B., & Fox, G. A. (2015). Modeling streambank erosion and failure along protected and unprotected composite streambanks. Advances in Water Resources, 81, 114-127.
• Fox, G. A., & Penn, C. J. (2013). Empirical model for quantifying total phosphorus reduction by vegetative filter strips. Transactions of the ASABE, 56(4), 1461-1469.
• Fox, G. A., Purvis, R. A., & Penn, C. J. (2016). Streambanks: A net source of sediment and phosphorus to streams and rivers. Journal of environmental management, 181, 602-614.
• Guertault, L., Fox, G. A., Halihan, T., & Muñoz-Carpena, R. (2021). Quantifying the importance of preferential flow in a riparian buffer. Transactions of the ASABE, 64(3), 937-947.
• Purvis, R. A., Fox, G. A., Penn, C. J., Storm, D. E., & Parnell, A. (2016). Estimating streambank phosphorus loads at the watershed scale with uncertainty analysis approach. Journal of Hydrologic Engineering, 21(9), 04016028.

Managing agricultural phosphorus (P) loss at the field scale is critically important to inhibit the development of algal blooms in freshwater bodies. This is particularly important in the Northern Great Plains region of North America which has an abundance of freshwater lakes, agricultural lands, and harmful algal blooms. Nevertheless, relatively little has been reported on agricultural phosphorus (P) loss within this region. This study summarized and evaluated regional trends in edge-of-field P-loss from tile-drained farms in the state of Minnesota between 1999 and 2021. Data used in this study were compiled from several past and ongoing initiatives that span four agricultural and geographic regions: Northwest (Red River Valley), Central (Sand Plains), Southwest (Minnesota River & Buffalo Ridge) and Southeast (Driftless Area). The findings of this study reveal that field-scale agricultural P loss in the state of Minnesota is primarily climate-driven. A north-to-south gradient is evident in regional P losses within the state that mirrors patterns of cold-climate hydrology that can be observed at the continental scale. Cold-climate hydrology reduces the magnitude of edge-of-field P loss from tile-drained farms in the Red River Valley. These patterns suggest that as the climate warms, a transition away from cold-climate hydrology may occur that could exacerbate future P loss from tile-drained farms.

Current tools and models used for predicting environmental losses of phosphorus (P) and making fertilizer recommendations typically utilize empirical relationships at the macro-level, with little to no consideration for differences between soil properties and management techniques that impact soil properties. While it is understood that purely mechanistic models are generally not feasible for application over the landscape or among diverse soils and conditions, basic soil processes could be further incorporated into existing tools and models for improving precision and accuracy.  This presentation explores several quantifiable processes that could be incorporated into existing nutrient transport models, as well as for creation of new agronomic tools for making nutrient recommendations and guidelines that are less empirical.  Specifically, consideration for soil sorption-desorption kinetics, P diffusion through the rhizosphere, plant uptake kinetics, and thermodynamic equilibrium between soil and solution phase, could be applied generally through consideration of easily obtainable soil properties such as soil type and classification, pH, organic matter, extractable P concentrations and current management.

Lake Mitchell is a 877 acre reservoir in northwest Davison County, South Dakota.  Constructed in 1929, the 93 year old reservoir has been subject to repeated blue-algae blooms in recent years, due to the presence of abundant nutrients in the water column and sediment.  The City of Mitchell has embarked on a multi-faceted project to improve water quality in the lake and accompanying Firesteel Creek watershed.  In 2018, a non-profit was formed to assist in funding and management in the watershed, the Friends of the Firesteel.  In 2020, we presented on the beginning of the partnership and the current state of the lake.  At present, plans are in place for constructed wetlands upstream of the lake, and preliminary dredging plans for the lake bottom are in place.  Additional partnerships are furthering the lake restoration project, as Ducks Unlimited and the state Game, Fish and Parks are getting involved on wetland construction and lake restoration.  Additionally, local educational institutions are increasingly becoming involved in the clean up process.

Zebra mussels are one of the most high impact and widespread aquatic invasive species in North America. Introduced to the Great Lakes in the 1980s by transatlantic cargo ships, they have quickly spread throughout the Great Lakes basin, infesting hundreds of lakes across the Upper Midwest, primarily via recreational watercraft. This vector has brought zebra mussels to South Dakota, where mussels are now spreading across the lake-dense eastern part of the state, as well as high profile reservoirs and rivers in central and western South Dakota. Zebra mussels could have major impacts to South Dakota economies and social/cultural values including irrigation dependent agriculture, recreational fishing and other lake-based tourism, and water quality impacts. As highly efficient filter feeders, zebra mussel populations can have dramatic impacts to nutrient cycling in lakes and can also increase the risk of harmful algae blooms. This talk will explain the mechanisms behind these impacts and highlight several key research projects completed or underway at the Minnesota Aquatic Invasive Species Research Center in zebra mussel prevention, control, and eradication.

The amount of phosphorus fertilizer sold in Minnesota has been approximately 325,000 short ton of P2O5 each year for the last decade. With increasing costs of inputs and the drive to preserve crop production resources, there is increasing interest in quantifying the losses of phosphorus under different crop management practices. To meet this need, a characterization of on-farm surface and subsurface drain water quality is underway.  The impact of crop rotation, tillage practices, weather conditions, and runoff pathways is being quantified though several multi-year edge-of-field monitoring programs covering 141 site years. The monitoring data shows that while no-till reduces soil loss through erosion compared to conventional tilled (median 38 lb. soil/acre vs. 219 lb. soil/acre), the median total phosphorus and dissolved phosphorus losses are 1.2 lb./ac and 0.81 lb./ac from no-till compared to 0.8 lb./ac and 0.27 lb./ac for conventional till. At a site with a 10-yr continuous monitoring record, row crops without cover crops lost between 2.6 and 3.9 lb. P/ac compared to 0.5 lb. P/ac under alfalfa. 41% of total phosphorus lost via surface runoff occurred while the ground was frozen. A study of using controlled drainage to adjust the outlet elevation preliminary showed a small increase in phosphorus loss under controlled drainage compared to conventional drainage. Information collected through the ongoing edge-of-field monitoring will lead to clearer information about phosphorus best management practices.

Changes in climate and land management practices have identified the need to reevaluate the accuracy of current corn (Zea mays L.) P fertilizer recommendations in South Dakota (SD). Also, an increase in soil health understanding has created the potential for soil health measurements to be used to improve the accuracy of these recommendations. The objectives for this study were to 1) evaluate the current P critical value and 2) determine the effect of including soil health indicators on the accuracy of predicting yield responses to fertilization. This project was conducted throughout central and eastern SD from 2019-2021 at 97 experimental areas that varied in management, landform, and soil type. A fertilizer addition treatment of 112 kg P2O5 ha-1 was compared to a control with no P fertilizer. Soil health and fertility samples (0-15 cm) were collected before fertilization and analyzed for physical, chemical, and biological characteristics. Positive yield responses to P fertilization were observed at many soil test P (STP) levels beyond the current critical value of 16 mg kg-1, indicating a critical value of 20 mg kg-1 would better fit our dataset. However, there was no change in RSE (0.145) and model accuracy was only improved by 1%, meaning there was not sufficient evidence to merit a critical value change. Random forest variable importance methods found differences among variables, although they were not significant. Decision tree analysis found several variables (Olsen P, CEC, soil respiration, and clay content), that when split using a decision tree, improved prediction accuracy to 74% compared to 63% when using Olsen P alone. These results demonstrate that soil health indicators along with soil fertility testing improves the accuracy of our yield response predictions to P fertilizer.

Chad Penn, Research Soil Chemist at USDA-ARS and Adjunct professor at Purdue University

"phosphorus dynamics at the soil scale"

Bio:  Dr. Penn is a research scientist at the USDA Agricultural Research Service in West Lafayette, and adjunct professor in the Department of Agronomy at Purdue University. Before joining USDA in 2016, he was professor of soil and environmental chemistry at Oklahoma State University since 2005. His current research is focused on soil chemistry and fertility for improving plant nutrient recommendations, nutrient transport, thermodynamics of surface reactions, design and construction of phosphorus removal structures, animal waste management and use of gypsum in agriculture. 

Lindsay Pease, Assistant Professor, Extension Specialist in Nutrient and Water Management, University of Minnesota

"phosphorus and tile drainage at the field scale"

Bio: Dr. Lindsay Pease is an Assistant Professor and Extension Specialist in Nutrient and Water Management. Her work focuses primarily on nitrogen and phosphorus management in row crop systems with an emphasis on nutrient loss in agricultural runoff. She is excited to work with Minnesota farmers to build resilient, sustainable agricultural production systems.

 

Garey Fox, Professional Engineer, Professor and Department Head, Department of Biological and Agricultural Engineering, North Carolina State University

"phosphorus at the reach scale: streambank contribution to phosphorus loading"

Bio: His research specializes in stream/aquifer interaction; stream bank erosion and failure; seepage erosion; subsurface nutrient transport; vegetative filter strips; and contaminant transport modeling. His research has been supported by the National Science Foundation (NSF), the US Environmental Protection Agency (EPA), the US Geological Survey (USGS), and the United States Department of Agriculture (USDA). He has published over 120 peer-reviewed articles in a number of refereed journals and also served as PI/co-PI on over $26 million in funded grant projects.

Heidi Peterson, Vice President - Agricultural Research and Conservation, Sand County Foundation, Madison, WI

"phosphorus at the watershed scale"

Bio: Dr. Heidi M. Peterson leads Sand County Foundation’s agricultural conservation team and sets its strategic direction in research, and farmer and rancher engagement. She brings significant leadership, teaching, and research experience surrounding agricultural conservation and water quality issues. Heidi previously served as the Phosphorus Program Director with the International Plant Nutrition Institute, and prior to that at the Minnesota Department of Agriculture. She serves the scientific community on the Agronomic Science Foundation's Board of Trustees, as an adjunct professor at the University of Minnesota, and as an associate editor with the Journal of Environmental Quality. Heidi completed her Ph.D. in Biosystems and Agricultural Engineering at the University of Minnesota. At Purdue University she received a MS degree in agronomy, and a B.S. degree in natural resources and environmental science.
 

Paul Fixen, Retired Senior Vice President at International Plant Nutrition Institute

"phosphorus at the global scale, trends over time, phosphate consumption and global reserves"

Bio: Paul Fixen is retired from serving as Senior Vice President of the International Plant Nutrition Institute where his responsibilities included coordination of the Institute’s programs in the Americas and Australia and serving as director of the Institute’s global research efforts. Dr. Fixen also served as the 2016 President of the American Society of Agronomy (ASA), the largest agronomic professional and scientific society in the world.

His career has emphasized the science of nutrient stewardship and how soil fertility and fertilizer use fit into the overall scheme of crop production systems and the environment. In 2007, he authored a concept for a global framework for nutrient best management practices that was a major resource behind what is now referred to internationally as 4R Nutrient Stewardship. The framework broadened the definition of “right” to include multiple performance objectives defined by stakeholders and encompassing the basic pillars of sustainability. He served as a co-editor and chapter author for the IPNI book, 4R Plant Nutrition – a Manual for Improving the Management of Plant Nutrition, which has been translated into multiple languages and is viewed as the primary reference for 4R Nutrient Stewardship.
     
Paul grew up in southwestern Minnesota on a crop and livestock farm and served in faculty positions at the University of Wisconsin and South Dakota State University prior to joining the Institute. He is a Fellow in the American Society of Agronomy, the Soil Science Society of America, the American Association for the Advancement of Science and the Fluid Fertilizer Foundation. A Melvin Jones Fellow, Paul is an active member of Lions Clubs International.

Abstracts: The deadline for submitting an abstract is Sept. 15, 2022 at 5 p.m. CST. Abstracts are limited to a maximum of 1,500 characters and must be submitted via the online form found below. Oral presentations will be limited to 15 minutes plus 5 minutes for questions.

Submissions Closed