Background: Purpose of the PMT?
The PMT originating from the Phosphorus Index concept of the 1990s, and in particular to the conditions across Maryland, is a tool to determine critical areas of phosphorus (P) loss from agricultural fields due to P source factors (agricultural management, fertilizer sources, rates, methods, and timing), and P transport factors, or field conditions conducive to P transport (soils, hydrology, and topography). Fitting into a farmer’s nutrient management plan, the PMT is used only on fields with higher soil P levels (greater than 150 Fertility Index Values (FIV)), identifying areas of high risk for P loss where reductions in manure/fertilizer applications and placement of best management practices (BMPs) would be well suited to reduce or eliminate any P loss. Ultimately, the PMT determines the risk of P loss from different fields and provides management recommendations (fertilizer/manure application rates, timing, and method; tillage practices; and other BMPs) to farmers to reduce potential P loss. Recent scientific findings at UMES and other institutions have led to modifications to the PMT including representation of subsurface P transport as a result of research on ditch drainage and ‘legacy’ phosphorus.
UMES-CWQC collaborative research over the past 20 years with the USDA-ARS Pasture Systems and Watershed Management Research Unit (PSWMRU) has focused on how to reduce the amounts of N and P entering the Chesapeake Bay and its tributaries. Specifically, the UMES-CWQC, PSWMRU and local farmers have collaborated to develop new techniques that help to mitigate nutrient losses to the Bay. Research efforts focused on improving nutrient management on the Delmarva Peninsula to improve the health of the Chesapeake Bay. UMES-CWQC has played a significant role in progress toward achieving the Chesapeake Bay Total Maximum Daily Load (TMDL), which requires a significant reduction in nutrient and sediment pollution to the Bay by 2025.
Examples of how UMES contributed to development of the PMT and improving the health of the Chesapeake Bay?
With over 20 years of research focused on improving nutrient management on the Delmarva Peninsula to improve the health of the Chesapeake Bay, UMES-CWQC research has underpinned various versions of Maryland’s Phosphorus Index, including the PMT, introduced the region to the potential to directly incorporate dry poultry litter into soils using a prototype technology, the “Subsurfer” (photo right), tested for over 10 years at the UMES-CWQC. This technique places dry poultry litter beneath the soil surface, without first broadcasting it on the soil where it is vulnerable to environmental transport, resulting in P reductions to surface waters by as much as 80%, and corn yield increases by 20% to 30% depending on soil type and environmental conditions. UMES-CWQC research resulted in Maryland’s support for this technology in the Maryland Watershed Implementation Plan that was part of the Chesapeake TMDL. UMES led several grants (approaching 8 million) from which versions of the Subsurfer were purchased by several land-grant universities in the Chesapeake Bay Watershed. While this technology is still being developed, without UMES research efforts it would still be in its earliest stages of improvement. These activities revealed to the Northeast Region and beyond the critical need to mitigate “legacy phosphorus” if watershed management programs are to be successful. Research from UMES on ditch management resulted in the first national meeting on ditch management which included the attendance of prestigious P scientist that comprise SERA -17. The findings from UMES research illustrated the need to improve drainage management in Maryland, with an emphasis on updating aging infrastructure and developing new and innovative solutions for nutrient hot spots. UMES research produced new ditch management practices; including gypsum curtains (a gypsum barrier 1-foot wide, 3 to 5 feet deep and inserted parallel to ditch or tile drain, see photo below), filters for nitrogen, and coupled N and P bioreactors – phosphorus filters. Our results at this point are promising, but cautionary for existing ditch management practices.
Most importantly, ditch research at UMES combined with its research on P leaching provided the foundation for the coastal plain component of the Maryland PMT. UMES research was a key feature in the 2015 Maryland Phosphorus Summit for then newly-elected Governor Hogan, who made agricultural P management a campaign issue. His capitulation over P management was, in part, a result of the compelling nature of UMES research. UMES researchers in collaboration with scientists from the USDA-ARS PSWMRU were part of the first team to identify “legacy phosphorus,” which is P retained in soils and sediments as a result of intensive litter/fertilizer applications well above crop nutrient requirements. Research with gypsum has spurred widespread use of this amendment to reduce P transport. UMES Co-led the team that developed a national conservation practice standard for gypsum application which has been approved by the Natural Resource Conservation Service. Controlling nutrient loss from artificially drained agricultural lands requires a comprehensive approach that balances drainage, water quality and production priorities. Recent work on the Atlantic Coastal Plain of Delaware, Maryland and Virginia demonstrates significant edge-of-field reductions in N and P export using drainage control structures, permeable reactive barriers and bioreactors in tandem with gypsum curtains, e.g. (Figure right). For the past eight years, many collaborative studies of this nature have been conducted at the UMES-CWQC. Edge-of-field and in-ditch approaches to losses of both N and P have resulted in very positive results that could influence future modification in the PMT, thus giving farmers fewer restrictions when applying manure if such practices are adopted.
What additional research is needed?
A new technique called inversion tillage is being tested at UMES in concert with USDA-ARS collaborators that could also be relevant to the PMT. This approach aims to reduce the extremely high amounts of P that move to drainage ditches and surface waters via runoff from poultry litter storage structures, and other point sources that pollute adjacent cropland soils which can range from 500 to over 2,000 ppm Mehlich-3 soil P test in the topsoil layers. Our general approach is to deep till (> 12 inches) every several years to move nutrients, especially P, from the surface where they have accumulated and are not easily available to crop roots, to deeper depths where roots grow, and mix the subsoil with surface soil to promote binding of the dissolved P. This will move the high-level surface P to lower depths where roots can better access it and prevent shallow leaching or lateral transport of dissolved P by mixing it with subsoil (clay) that has a high P binding potential. Subsequently, we will bring the new surface horizons back to full fertility potential by adding fertilizers (N-based), lime, organic matter and other applicable additives.
To download a list of refereed publications associated with the Phosphorus Management Tool and produced by the Chesapeake Water Quality Center, click here!
