Fertilizers destabilize natural grasslands

A new study has found that fertilizer could be too much of a good thing for the world's grasslands.

The worldwide study showed that, on average, additional nitrogen will increase the amount of grass that can be grown. But a smaller number of species thrive, crowding out others that are better adapted to survive in harsher times. It results in wilder swings in the amount of available forage.

"More nitrogen means more production, but it's less stable," Johannes M.H. Knops, a University of Nebraska-Lincoln biologist and one of the paper's international co-authors, said.

The three-year study monitored real-world grasslands at 41 locations on five continents. The sites included alpine grasslands in China, tallgrass prairies in the United States, pasture in Switzerland, savanna in Tanzania and old fields in Germany.

Two sites in Nebraska were part of the study, the Cedar Point Biological Station near Ogallala and the Barta Brothers Ranch in the Sandhills near Valentine.

The study found natural-unfertilized-grasslands with a variety of grass species have more stability because of species "asynchrony," which means that different species thrive at different times so that the grassland produces more consistently over time.

Fertilized plots saw declines in the numbers of species compared to unfertilized control plots.

The study was published in the journal Nature.