Soil sampling key in controlling phosphorus loss

By Matt Reese

Improving water quality starts with getting an accurate soil sample. This is a crucial step in avoiding costly over application of phosphorus and environmental challenges in the coming years. This was an important part of the discussion surrounding the improvement of water quality in Lake Erie at the Soil and Water Conservation Society this week at the Ohio Department of Agriculture.

“If phosphorus is surface applied, chances are that phosphorus levels are much higher than indicated in an 8-inch soil sample,” said Kevin Elder, with the Ohio Department of Agriculture. “The surface may test very differently than the typical 8-inch sample. When you’re soil sampling, you should do a surface test too.”

Having the proper information is vital for the implementation of the 4R Nutrient Stewardship Program that will be increasingly important for farmers in the future. Elder outlined the 4R concept that promotes using the right fertilizer source, at the right rate, at the right time, with the right placement. Recent studies indicate that the timing of fertilizer application, and how well it is incorporated into the soil layer, significantly reduces dissolved phosphorus runoff. Specific farm level recommendations include:

• Take frequent soil tests and follow soil fertilization rates based on OSU guidelines;

• No spreading of fertilizer on frozen or snow covered ground;

• Maintain good fertilization records;

• As much as possible incorporate fertilizer into the soil layer.

“There are a lot of questions yet, but there are some things we do know,” Elder said. “We do know that farmers met the phosphorus goals set in the 70s, but now the issues have changed from sediment to dissolved phosphorus. We know that no-till and minimum-till may not sufficiently mix nutrients in soil. We know that the phosphorus our corn and soybeans use is the same phosphorus that gets in the Lake and grows algae. We know we need to soil test and apply only what is needed keep levels below 50 parts per million, and we know we need more research on dissolved phosphorus.”

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