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Making a Difference in Improving Water Quality

Mark Wilson with farm equipment (pre-COVID) in Ohio.

As a farmer, have you ever wondered if you are truly making a difference in improving water quality when you subsurface apply fertilizer, plant a cover crop, practice the “4R’s”, or install a filter strip?  Most farmers I talk with want to be good stewards of the land, but beyond adopting the conservation practices recommended by “experts,” farmers rarely receive actual confirmation that they are doing the right thing.

One way to confirm if your practices are reducing the nutrients leaving your land and entering a stream or river is through edge-of-field monitoring.  Edge-of-field monitoring involves intercepting and channeling runoff from the edge of an agricultural field through monitoring equipment before it enters the natural stream network.  Edge-of-field monitoring can be very informative, but it also can be very expensive, even for one field.

If you want to confirm whether conservation practices reduce nutrient loading on a large scale, say the 600,000-plus-acre Upper Scioto River Watershed, or USRW, you need a watershed computer model.  Now I know, junk-in equals junk-out; but such models, and the input data they depend on, have gotten quite sophisticated— this is especially true for the Soil and Water Assessment Tool, or SWAT. We at AFT have successfully completed SWAT Version 1 for the USRW and I think the results are very interesting.

Results from SWAT Version 1 indicate that nonpoint source nutrient loading is predominant over point-source nutrient loading in the USRW. Put another way, nutrient loading from land runoff far exceeds nutrient loading from municipal and industrial discharge pipes.  Because 80% of the land in the USRW is agricultural, farmers have a real opportunity to make a difference in terms of water quality by reducing the amount of nutrients leaving their land and entering the water.

Mark Wilson (pre-COVID) farmer workshop in Ohio.

SWAT Version 1 suggests certain areas of the USRW have particularly large nutrient loads per acre relative to other areas. Some of the highest nutrient concentrations originate in the headwaters of sub-watersheds where smaller streams have less flow to dilute the loads.

Once the SWAT model is calibrated (i.e. simulated nutrient concentrations match observed or actual nutrient concentrations), various land management scenarios can be simulated, and the resulting nutrient loads can be evaluated.  Several different crop rotations, tillage methods, fertilizer applications, and conservation practices were simulated in SWAT Version 1.  One of the most promising simulations was substituting fall applied Triple Super Phosphate, or TSP, for fall applied Monoammonium Phosphate, or MAP, and Diammonium Phosphate, or DAP.

Farmers typically use MAP and DAP in the fall to supply phosphorus for next year’s crop.  TSP is a familiar and time-proven fertilizer to a certain generation of farmers, many of whom recall “Triple” with nostalgia.  TSP has not been widely available in recent years, but it can be obtained.  And because it has 0% nitrogen (N) and MAP and DAP have 11% and 18% N respectively, substituting TSP will eliminate the N applied through MAP and DAP, which often went unused by a growing crop.

Over the next two years, AFT will utilize funding from an Ohio NRCS Conservation Innovation Grant to bring TSP into the USRW and incentivize farmers to substitute it for MAP and DAP.  If you are a farmer and participate in this project, you will be making a difference that can be scientifically confirmed because of SWAT Version 1. You will be able to continue to be good stewards of the land and improve water quality in the USRW.

About the Author
Mark Wilson

Farming for Cleaner Water Project Manager

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