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The 4 Rs of phosphorus PDF Print E-mail
Thursday, March 14, 2013 12:40 PM

The following article was written by Ed Lentz, Hancock County Extension Educator and edited by Jim Hoorman.

PUTNAM COUNTY — Waterways and lakes have always been important resources for northwestern Ohio. About 11 million people in the USA and Canada use Lake Erie water as their primary drinking source so clean water is a concern. Evidence for this concern was the large algae bloom that occurred in Lake Erie in 2011 but not in 2012. Algae blooms are a concern since some species are toxic to people and they interfere with recreational activities. In smaller bodies of water the algae may deplete oxygen levels as they decay, which may result in fish kills. Algae blooms generally occur in the presence of excess nutrients, especially phosphorus. Phosphorus (P) sources may originate from industrial, municipal, and agricultural systems.

In agriculture, P is required to produce high yielding crops. Phosphorus not used by the crop is generally tied up or trapped by the soil. This tie up generally minimized P loss unless soil leaves the field by water or wind erosion. Farmers have started using reduced tillage and/or cover crops to reduce soil erosion. However, P now remains on or near the surface after application which may result in losses with heavy rain events. About 90 percent of most P runoff occurs during 10 percent of the most intense rainfall events and about 80 percent of the P comes from only 20 percent of the land (Sharpley, 2013). In 2011, heavy spring rains delayed planting until early June and may have contributed to the algae problems.

Farmers care about our soils and environment, and P fertilizer is an expensive input; so it costs money when fertilizer leaves a field. To manage their nutrient program and to be good environmental stewards, farmers follow what is called the 4R program — the right rate, right time, right place and the right source

The right rate is determined by testing soils for P levels and matching these levels to crop needs. Ohio State University research and the Tri-state Fertility Guide instruct farmers and fertilizer dealers how to apply soil P based on the needs of a particular crop. Farmers use the right time by avoiding application when the risk for loss is the greatest. Application times that pose the greatest risk is on frozen or snow-covered ground and prior to heavy rain events, but it may be difficult to predict rain events.

New technology has allowed farmers to strategically place fertilizer. Global positioning systems have allowed farmers to grid and precisely apply P only in the areas of the field that need fertilizer. Strip tillage and other systems have allowed them to diminish erosion losses and place fertilizer in bands near growing roots. The plant food industry has worked closely with farmers to provide products that are effective for providing P for the crop. As new technologies emerge, farmers will have more sources available that reduce the risks of nutrients leaving the field. The 4R program has been very effective in keeping nutrients in the field. However, weather greatly affects crop production and water quality. Our best management practices may not be enough in years of unusual weather. Many accuse agriculture as the cause of the Lake Erie algae blooms in 2011. It probably played a part along with the other potential sources of P entering the watershed. However, the general public needs to be reminded in 2011; this part of Ohio set a new record for the most rainfall in a given year with a large number of storms with heavy rainfall. Notice that in 2012 and other years without the large number of storms and heavy rains, algae blooms were not an issue.

Farmers and the agricultural industry care about the waterways and lakes of northwestern Ohio and realize that they need more information. Extensive research is being funded to find efficient ways to minimize potential loss of nutrients from fields. Some policy makers still believe the solution to the 2011 algae blooms is to establish more regulations on farmers. It might be prudent to see the results of P research being conducted by Ohio State University and various conservation and environmental groups before adding regulations.


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