Grazing Animals vs. Chemical Fertilizers: Guess Which One Improves Soil Biodiversity?


Nitrogen or phosphorus based chemical fertilizers and grazing animals including kangaroos, deer, sheep and zebras were the subject of an extensive worldwide study on the health of plant species in prairies, savannas, alpine meadows and other grasslands.

The findings may help scientists better understand how to boost crops grown for food in these regions, while also protecting threatened animal and plant species, as well as bring relief to struggling ecosystems.

Conducted by a team including Trinity College Dublin professor of zoology, Yvonne Buckley, the findings were published in the recent issue of the journal Nature (“Herbivores and nutrients control grassland plant diversity via light limitation“).

Spanning six continents and 40 grassland areas, the team set up research plots that contained fertilized and unfertilized soil, as well as fenced and unfenced areas to restrict and encourage herbivores. The researchers noted that the study “demonstrates that nutrients and herbivores can serve as counteracting forces to control local plant diversity through light limitation, independent of site productivity, soil nitrogen, herbivore type and climate.”

Since 2005, the researchers have measured the areas for the amount of plant material that’s grown, the amount of light that reached the ground, and the plant diversity growing in the regions.

The scientists used the Nutrient Network (“NutNet” is a grassroots campaign supported by scientists who volunteer their time and resources), to model and predict how the planet’s grasslands would likely respond to global warming.

“We found that fertiliser reduced the diversity of plant species in the plots because species less able to tolerate a lack of light were literally overshadowed by fast-growing neighbours,” said Professor Buckley.

“But whenever herbivores increased the amount of light that struck the ground, by eating plants, the total plant species diversity increased. What was especially interesting – and convincing – was that these results held true from Australia to Europe, China and the US, and whether the herbivores involved were rabbits, sheep, elephants or kangaroos.”

The researchers noted that the study’s results “show that grassland biodiversity is likely largely determined by the offsetting influences of nutrition and grazing on light capture by plants.” That information could help farmers to better fertilize their crops and reduce the use of chemical fertilizers that come with environmental and human health risks.

Find Jill on Twitter @jillettinger

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Image: Rob Wei