Phosphorus-sorbing Materials in Ag Ditches (PSMs)


These in-channel engineered systems can capture significant amounts of dissolved phosphorus in agricultural drainage water by passing them through phosphorus-absorbing materials, such as gypsum, drinking water treatment residuals or acid mine drainage residuals. Phosphorus-absorbing systems can potentially remove large percentages of phosphorus as well as sediment, heavy metals and other pollutants.

Initiation protocol:

The proposed practice is applied on a per acre basis, and can be implemented and reported for cropland on both low-till and high-till land uses that receive or do not receive manure.

Public acceptance:

As this practice is not yet widely distributed in the region there is no real public feedback on its acceptance currently. However, as this practice is placed at a ditch outfall, there is likely little to no resistance for its implementation.

Implementation Factors (level of difficulty):


Funding Sources / Options:

Grants are available through the Maryland Agricultural Cost-Share (MACS) Program. Potential funding also exists through Farm Bill programs.


Costs estimated as $ per acre of practice installed. 

Cost Estimates EPA MDA Average
Initial $- $625 $625
Annual $- $- $-
Lifespan (yrs) 1 5
Annualized $- $-  $-

Load Reduction Efficiency:

The current placeholder effectiveness value for this practice has been proposed at 0 percent total nitrogen, 40 percent total phosphorus and zero percent total suspended solids, utilizing a conservative estimate in phosphorus removal measured by the UMD/ARS research project as a reference. Based upon the documentation, the proposed practice is currently limited to coastal plain soils with shallow groundwater levels requiring drainage ditches for agricultural production.

Average Total Nitrogen removed per acre of practice per year = N/A

Average Total Phosphorous removed per acre of practice per year


0.15 lbs.


0.46 lbs.


0.86 lbs.

Cost per pound removed = between $125 and $833

Average Total Suspended Solids removed per acre of practice per year = N/A

Operation & Maintenance:

Periodic replacement of the absorbing material as its lifespan nears its end and keeping the material free of clogs are the largest maintenance burden of this practice experienced thus far.


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