The Impact of Cover Crops on Phosphorus


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, so a team of researchers recently released results of a 2-year field study about 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 2 years of study, the findings revealed cover crops did reduce soil and phosphorus loss more in tilled than no-till fields.

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 that reveal P2O5 levels less than 30 ppm, Penn State University recommends taking into account what the crop naturally removes, plus an additional amount to bring the soil test level to the optimum range. But when soil tests show rates of P2O5 higher than 50 ppm, corn and soybeans will eventually consume phosphorus until the optimum nutrient range is reached.
Contact your Golden Harvest Seed Advisor with questions or for additional agronomic insights.
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