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The Impact of Cover Crops on Soil Phosphorus Runoff

Cover crops such as rye, radishes and oats are notorious for reducing the amount of nitrogen lost to subsurface drainage. But what about phosphorus? Iowa State University wanted to find out. A team of their researchers released a 2-year field study how cover crops affect surface runoff in relation to phosphorus nutrient loss. 

Led by Iowa State University Agronomy Professor Antonio Mallarino, the study focused on how the cover crop winter cereal rye influenced phosphorus loss. Phosphorus is critical for corn and soybeans because the nutrient helps develop roots and seeds from the start, maximizing grain fill at the end of the season and ultimately, yield.  

The university study was conducted on 12 one- to three-acre areas at Iowa State’s Hermann Farm in highly phosphorus corn and soybean rotation fields. Since cover crops reduce soil loss, researchers have also suspected cover crops decrease phosphorus loss. Iowa State University was motivated to examine this hypothesis. After the 2-year study, the findings revealed cover crops did reduce soil loss in tilled and no-till fields. In a tilled field, cover crops also reduce phosphorus loss, but the impact cover crops play on phosphorus loss in no-till fields is unclear.

When phosphorus levels range between 30 and 50 ppm, Penn State University recommends offsetting natural corn and soybean nutrient consumption. The chart below shows average natural phosphorus consumption by crop: 

See if your fields need more phosphorus by taking consistent and representative soil samples. For results with P2O5 levels less than 30 ppm, take into account what the crop naturally removes, plus an additional amount to bring the soil test level to the optimum range. Consider utilizing cover crops in tillage systems to help retain soil nutrients from runoff.

Contact your Golden Harvest Seed Advisor with questions or for additional agronomic insights.

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