AGRI-BRIEFS
  AGRONOMIC NEWS ITEMS
From Agronomists of the
Potash & Phosphate Institute
655 Engineering Drive, Suite 110
Norcross, Georgia 30092-2837
Phone (770) 447-0335

Summer 2001, No. 1

GLOBAL NUTRIENT OVERLOAD

Human activities, including agriculture, increase nutrient delivery to the ecosystems of the planet. Recent reports raise concerns about the impact of the increasing global nutrient load. Is nutrient overloading a real worry? What are the impacts?

In Canada, five federal ministries recently completed an assessment of nitrogen and phosphorus loadings. Their report concludes: “…nutrients are causing problems in certain Canadian ecosystems and affecting quality of life for many Canadians.”

An article in a recent issue of Science reported that if trends of fertilizer consumption from the past 35 years are projected, there would be 2.7 times as much nitrogen used in 2050 as at present, and 2.4 times as much phosphorus. The article went on to forecast that this increased nutrient use would drive an identical increase in eutrophication (nutrient enrichment) of the world’s ecosystems, resulting in habitat destruction and species extinctions…loss of biodiversity.

Biodiversity is important, and we share the concern. But will the projected scenario really happen? Here’s why it shouldn’t.

The authors of the Science report made a mistake in projecting the fertilizer trend. They assumed that global use of fertilizer would continue to increase without slowing. Actually, world consumption figures for phosphorus already show a distinct slowing in growth rate. The world today (excluding the former Soviet Union) produces 25 percent more crop per unit of phosphorus fertilizer applied than it did twenty years ago. Simply put, farmers are improving their nutrient use efficiency.

It cannot be denied that nutrient loadings harm water quality in many watersheds and that cropland contributes part of those loadings. The future will demand continued improvement in the ratio of food output per unit of nutrient input. The tools of precision agriculture are helping to ecologically intensify agriculture, producing higher yields on less land to save habitat for wildlife.

Habitat is key to maintaining biodiversity. As stated in another Science article back in 1997, “Land transformation is the single most important cause of species extinction.” Today’s crop producers increasingly use buffer zones around watercourses, reducing nutrient delivery to streams and providing diverse habitat for wildlife. In the year 2000 alone, the USDA-NRCS helped farmers install conservation buffers on one million acres of land.

In some watersheds, nutrient additions benefit biodiversity. In British Columbia’s Kootenay and Arrow lakes, for example, fisheries managers have been adding phosphorus fertilizers to improve habitat for game fish such as salmon and rainbow trout. Fisheries agencies have cautioned that reductions in phosphorus loadings to Lake Erie would likely reduce populations of walleye and yellow perch.

Can it be claimed that higher nutrient levels reduce biodiversity? Species at the top of the food chain–walleye, yellow perch, salmon, and trout–are good indicators of the health of the whole ecosystem. An optimum level of nutrients is as important for biodiversity as for productivity. Defining the specific optimum for a watershed calls for cooperation among all end users.

Nurturing biodiversity while nourishing the global population is a continuing challenge for agriculture, but people who care for both will spare no effort in applying the best science to the management of nutrients.


—TWB—

For more information, contact Dr. Tom Bruulsema, Eastern Canada and Northeast U.S. Director, PPI, 18 Maplewood Drive, Guelph, Ontario N1G 1L8, Canada. Phone: (519) 821-5519; E-mail: tom.bruulsema@ppi-far.org.
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