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Phosphorous produces on-farm benefits with careful use

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Written by Jonathan Eisenthal

Like nitrogen, phosphorous pays off with better yielding crops, while also warranting careful use. This was one of the vital messages at the recent Nutrient Management Conference in St. Cloud, organized by the University of Minnesota and the Minnesota Agricultural Water Resource Center.

Heidie Peterson, who leads the phosphorous program at the International Plant Nutrition Institute, spoke to a room full of farmers and crop consultants to emphasize that point.

“Phosphorous is involved in photosynthesis, energy transfer, cell division and enlargement,” said Peterson. “It is really important for lipid formation and growth. It improves the quality of fruit and vegetable crops. It is vital for seed formation. It improves water use and it also speeds up maturity.”

When phosphorous escapes the farm field, however, it accelerates the natural process of aging in ponds and lakes called eutrophication. The additional phosphorous causes blooms of blue green algae that rob oxygen from the water and degrade it as wildlife habitat.

One of the trickiest elements of handling phosphorous is that it is not one thing, but two. Particulate phosphorous, thanks to its electric charge, clings to soil particles. If your soil loss is under control, particulate phosphates stay put. But the other kind of phosphorous, dissolved phosphorous—the form that is available for the plant to feed from—is just as slippery as nitrate nitrogen.

The chemistry of phosphorus in the soil is very complex, according to Peterson, and dissolved phosphorous can form less soluble products, so it’s not always instantly available. With that, regular soil testing is recommended to help the farmer maintain a sustainable level of phosphorous.

Through 600,000 on-farm soil tests over the past two decades, Peterson said they are able to model available phosphorous anywhere in the United States. The analysis shows that some 33 percent of farm land would see a yield benefit from adding more phosphorous, while another 25 percent have just the right amount, and the rest have more than needed.

One of the key recommendations of experts, said Peterson, is a guaranteed analysis of both manure and commercial fertilizer so the farmer knows exactly how much phosphorous they are applying.

Placement is another key consideration for nutrient stewardship. With phosphorous, incorporation below the soil surface is shown to be beneficial in study after study. Deep banding phosphorous caused plants to root deeper, and as a consequence they showed less yield loss during drought periods.

Farmers who avoid tillage or who use cover crops to promote healthier soil may see elevated dissolved phosphorous losses. The good news, according to Peterson, is that choosing covers that don’t die in the Minnesota winter, and injecting phosphorous instead of broadcasting it on the surface, can reduce nutrient loss while still giving the farmer the soil health benefits of those practices.

The Minnesota Corn Growers Association is a proud supporter of the Nutrient Management Conference as part of its mission to make the state’s corn farmers the most sustainable and environmentally responsible corn farmers in the nation.

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