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Phosphorus: Fact and fiction

October 17, 2008
From WAYNE SCHOPER Brown/Nicollet Extension Educator

There is a lot of research behind the fact the phosphorus is one of the main nutrients in profitable corn and soybean production. In reality, phosphorus plays an important role, not only in healthy plant growth of all kinds, but human and animal health as well.

But in today's world there is a lot of misinformation. Daniel Kaiser is a soil scientist at the University of Minnesota. He writes a regular article on the "AgBuzz" blog, a site on the Internet for extension staff and producers to write about the latest hot items in agriculture. In his article, Dan mentions that he was watching a TV show on the Discovery Channel. This particular program was discussing how cities treat wastewater and how they now have the technology to remove phosphorus from the waste water. Their specific comment concerned "phosphorus: a poisonous element in the nitrogen family".

It is hard to believe that this kind of misinformation was shown as part of an educational program on a respected TV channel. First of all, phosphorus is not a member of the "nitrogen" family. It is an element on its own and works together with nitrogen and other elements to support virtually anything that lives on the planet earth. And secondly, phosphorus is not a poisonous element.

Like anything in nature, the dose makes the poison. Caffeine, for example, if taken in large enough amounts can be poisonous. The old adage of moderation in everything comes to mind here.

It does prove a point that there is a lot of misinformation out there and you have to know what you are talking about before you mention something like this in a public forum. We all know that too much phosphorus in water can be and is a problem in some lakes and streams all over the U.S. But calling it a poison is not correct. The TV program was not about farming, but it did contain misleading and outright false information that can cast agriculture in a bad light.

Part of my job is keeping the general public informed about current topics in agriculture. I utilize a variety of resources to put together news articles and information for use by public media and others with an interest in information about agriculture. We have made many strides in managing phosphorus and conducting good research and reporting the information that we find is an important part of that process.

We have a strong livestock industry in Brown and Nicollet Counties. One of the byproducts of that industry is manure. We know that nutrient levels such as phosphorus vary widely between species of livestock. This is because of the different rations fed to, say turkeys versus dairy cattle. The type of bedding used for a particular livestock species will also affect the analysis of the manure. That is why we advocate testing manure to determine the levels of nutrients that are present. We are particularly interested in nitrogen (N), phosphorus (P) and potassium (K). When we run an analysis of a manure sample we will get a report of NPK levels present in the manure. That is why it is very important to take a good representative manure sample.

We can do this by good agitation if we are sampling liquid manure or by "grab" sampling if we are doing an analysis of dry manure. We then match up the manure analysis with soil test results to apply enough NPK to the soil to support a corn or soybean crop without over applying these nutrients and causing a pollution problem.

This means that we are doing a better job of managing crop nutrients from manure sources than ever before. With crop inputs, including fertilizer, at all time price highs, it just makes sense for livestock producers to make use of every pound of nutrients from manure sources.



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