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DRP in the WLEB


The DRP or Dissolved Reactive Phosphorus Issue

April 21, 2011 Satellite photo of Lake Erie

April 21, 2011, satellite photo of Lake Erie illustrating heavy sedimentation from recent heavy rainfalls.

In recent years there has been a documented increase in soluble phosphorus (DRP or dissolved reactive phosphorus) exported from Ohio Watersheds, resulting in an increase in harmful algal blooms. The increased use of no-tillage has been alleged as a cause for this increase due to a stratification of phosphorus at the surface in continuous no-tillage systems.

The data in the WLEB Tillage Survey casts doubt on that theory as the sole cause for the increased soluble phosphorus. While the data does not identify fields that might be in continuous no-till, the very low amount of no-till corn practiced, and the very large number of conventionally tilled planted corn acres would preclude very many fields from being in continuous no-till for very many years. Since corn and soybeans are frequently rotated, it is logical that most fields are a mixture of no-till and tillage over the life of the 3, 4, or 5 year rotation. These two crops account for roughly 86% of the acres in cultivation in the watershed, exclusive of minor crops. With one in four acres in the watershed in conventionally tilled corn each year,  there is still a whole lot of soil stirring going on out there.

There is no doubt that the increase in soluble phosphorus is real, but there are many factors, and probably a combination of factors, that could be driving it. These include:

  • Changes in methods of fertilizer application from banding through planters to broadcast surface applications, and from spring to fall or winter applications. These methods have become more popular as equipment has gotten larger, and each farmer is farming more acres, and trying to minimize time and labor requirements.
  • The trend towards applying two years of fertilizer in one year on the corn crop. This provides a cost savings in application labor and time needed to do application without suffering any agronomic yield reductions, which is an advantage to the applicator and the farmer. At the same time, it puts more material, at higher rates, out on the landscape longer.
  • More application in the winter months as custom applicators try to maximize efficiency and keep equipment and staff busy. Also, transportation issues, storage limitations, and pricing structures may influence the market to encourage fall or winter applications.
  • A gradual long term increase in soil phosphorus levels within the basin over a thirty-forty year period as farmers have attempted to maximize crop yields.
  • Larger equipment and the farming of more acres may be causing more soil compaction in the basin, decreasing infiltration, and increasing surface runoff in major storm events.

Steve Davis, Watershed Specialist with NRCS, believes that the increased use of conservation tillage systems could be one of the several contributing factors by increasing to some degree phosphorus stratification in the soil surface. However, he believes that the cause is more likely “all of the above.”  And, given the critical need to control sediment delivery to the basins streams, drainage ditches, and to Toledo Harbor, going backwards on no-tillage is not the answer. “We can’t trade one new problem to go back to another old one that we had before,” Davis maintains.

If anything, Davis says the uncertainty points out the need for substantial new and additional research needed by our Universities, our Land Grant Institutions and our Agricultural Research Institutions into the exact forces driving the changes in runoff and the Best Conservation Management Practices that will mitigate the problem.

The Good News and a Call to Action

In the interim, both the USDA-NRCS and the regions farmers are not standing still. Since 1996, Ohio NRCS has dedicated nearly $5 million in Environmental Quality Incentive Program funding to Northwest Ohio farmers to apply innovative conservation and nutrient management systems on 462,265 acres within the watershed. And progressive farmers, crop consultants and fertilizer dealers are stepping up and applying new conservation and nutrient management systems.  These systems include a bundle of conservation practices NRCS has developed for Ohio which combines precision nutrient management, cover crops, controlled traffic, and conservation tillage or strip tillage into one system.  When the system is used properly, only the nutrients needed are applied where they are needed, when they are needed.   The combination of all the practices improves infiltration and reduces surface runoff.

Farmers are purchasing new equipment and adapting technology to georeference soil sampling and map crop yield zones within each field. This “on the go” automated GPS technology can map where nutrients are needed at harvest and then automatically change application rates on the fertilizer spreader to apply that same amount in the same place when the fertilizer is applied.

Crop consultants and advisors are stepping up to advise farmers on these methods and to help farmers understand that their profits can be maximized by not how much fertilizer they apply, but by how efficiently and effectively they apply it, often using lesser amounts than before to produce the same or higher crop yields.

Davis said it is important to note that per acre soil and nutrient losses in the watershed are not high. But with so many cropland acres concentrated in one region, draining to one point, a little bit from each one adds up to a big problem in Lake Erie. And since so many acres are involved, many, many farmers will need to do their part if progress is to be achieved. This will require a large amount of conservation technical assistance, cost sharing incentives, and new and innovative machinery.