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No-till is a solution and a problem for phosphorus loss

By Matt Reese

Lake Erie has had increasing levels of harmful algae growth in the Western Basin, as seen in this aerial photo.

It seems that, with regard to the phosphorus problems in Lake Erie and other bodies of water, no-till is part of the solution and part of the problem.

Lake Erie was once known around the world for its pollution and water quality problems, but in the 1970s, farmers and industry teamed up to clean up the Lake. This was done by dramatically reducing the total amount phosphorus, much of it attached to soil particles. For farmers, conservation tillage and no-till were an important part of the solution. No-till reduces soil erosion, which reduces the amount of phosphorus attached to soil particles that are leaving the field.

The improvements in Lake Erie were amazing, but, unfortunately the problem is back, and this time it is the more vexing form of dissolved phosphorus. To complicate matters, no-till actually may facilitate the loss of dissolved phosphorus.

“There is no easy answer for this,” said Andrew Sharpley, a leading expert on phosphorus from the University of Arkansas. “Conservation tillage is one of the biggest benefits in terms of reducing erosion and reducing the total amounts of phosphorus getting into lakes. It has been a huge benefit, but what happens is that there is more soluble phosphorus getting in that can have an

Andrew Sharpley, a leading phosphorus expert from the University of Arkansas, talks at the Soil and Water Conservation Society meeting at the Ohio Department of Agriculture.

immediate impact on the lakes. It doesn’t mean we shouldn’t be doing conservation tillage, but there is a downside to conservation tillage that we need to be aware of. Plowing can reduce dissolved phosphorus, but plowing also increases erosion.”

Without being incorporated into the soil with tillage, broadcast phosphorus stays at or near the soil surface and is more easily dissolved in rainwater where it can leave the field through tile lines or in surface water.

“This makes the management of phosphorus fertilizers with no-till very important,” Sharpley said at this week’s Soil and Water Conservation Society meeting at the Ohio Department of Agriculture.

It only takes a very small amount of dissolved phosphorus in lakes to meet the nutrient needs of the oft-discussed toxic algae. Even a small percentage dissolved phosphorus losses from crop fields contribute to the problem. Field tile also plays a significant role.

“While farmers need to tile drain many soils to profitably grow crops, the tiles do connect a large amount of land to streams and can thus increase amounts of phosphorus entering streams,” he said. “Simple economics drives many of these decisions. Farming is a business and many environmental measures can cost farmers a lot of money. We need to find a way to help share the cost of putting in a range of conservation measures so that they can continue to provide us with abundant, safe food.”

Sharpley does suggest some practices that can help to address the problem.

“There are some options,” he said. “Cover crops are obviously a benefit. If you are fall applying nutrients they tie up those nutrients and release them slowly. Cover crops will reduce the loss over that winter period compared to leaving it bare, so they can be a great benefit. But, cover crops are not removing any phosphorus. If they are not harvested, they are just recycling the nutrients. They can act like a slow release fertilizer.”

It is also important to only apply phosphorus that is needed by the crop.

“One of the big things is soil testing – knowing what is in the soil – and adjusting the rates of application to what the crop needs,” he said. “While surface runoff picks up most of its phosphorus from the top one or two inches, plant roots can get phosphorus from much deeper.”

It will take great care, but with the proper measures, farmers can again find the solution to the problem that is also a solution.

 

 

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3 comments

  1. How true! One simple way to monitor improvement made by practices to reduce losses of dissolved and particulate phosphorus in runoff from cropland would be to soil test for the level of phosphorus in the upper 2 inches of the soil. Rising levels would suggest improved forms of nutrient management are required; falling levels would indicate that practices applied are working. One other point. Some cover crops can actually increase the availability of dissolved phosphorus at the soil surface.

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