Lincoln, Neb. — According to study findings published online by Nature, fertilizer could be too much of a good thing for the world’s grasslands. The worldwide study found that while on average additional nitrogen increases grass output, a smaller number of species thrive and crowd out others better adapted to survive harsher times. "More nitrogen means more production, but it’s less stable," said Johannes M.H. Knops, a University of Nebraska-Lincoln biologist and one of the paper’s international co-authors. "There are more good years and more bad years. Not all years are going to be good, and the bad years are going to be worse." The three-year study monitored real-world grasslands at 41 locations on five continents, including China, the U.S., Switzerland, Tanzania, and Germany. Researchers found common trends among grasslands around the world, including that different species on natural, unfertilized grasslands, produced more consistently over time; fertilized land saw a decline in the numbers of species compared to unfertilized plots; and fertilization tended to weaken the species diversity seen in unfertilized plots. Knops said that overusing fertilizer could intensify the effects of drought on grasslands and have ripple effects during bad years by reducing plant cover, which in turn increases erosion. The Nature article is one of several research articles on the relationships between grassland diversity, productivity, and stability generated by the Nutrient Network experiment, http://www.nutnet.org.
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