Study says excess phosphorus may reduce crop yields

Results suggest that excess levels can affect soil microbes

Researchers exchanged soil microbes among alfalfa plants treated with different levels of P.

Excessive phosphorus fertilizer may do more harm than good for crop yields, say scientists at Penn State University.

In a study published in Phytobiomes Journal, a team led by Terrence Bell and Jenny Kao-Kniffin found that soil treated with high amounts of phosphate can result in poorer plant performance and that it appears the soil micro-organisms from this treated soil can reduce plant yield.

A release from the American Phytopathological Society says the team grew four generations of alfalfa in soil with different concentrations of P. After each generation, a small amount of soil, including soil-borne micro-organisms, from pots containing the best-growing plants was transferred to the next generation. They then applied the micro-organisms selected under each nutrient condition to all other nutrient conditions to determine whether nutrient history changed the function of soil micro-organisms, even when a particular nutrient such as high-inorganic P was no longer applied.

The release says the team found that alfalfa plants grown in soil treated with high levels of inorganic P, or with the microbes from this treatment but in low P, performed worse than the plants grown in soil treated with lower or no levels of P. Using high-throughput DNA sequencing, they saw that the composition of micro-organisms grown under high inorganic P was distinct from other treatments.

“These findings require additional study, but for now they suggest that excessive P fertilizer could have lasting negative effects on crop productivity by reducing the micro-organisms (or how they function) that are critical to crop health,” the release says.

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