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Farm Advisory
April 17, 2002

Soil "Micro-Nutrient" Fertilizers

Spring has arrived, and farmers are making decisions on which inputs they should purchase -- including what type of fertilizer program to use for the new crop year. The bulk of soil nutrients purchased by farmers contain the "primary" soil nutrients -- nitrogen, potassium and phosphorus. However, some farmers also purchase other soil nutrients, often referred to as soil "micro-nutrients." Soil micro-nutrients include iron, copper, chloride, zinc, boron, manganese, and molybdenum.

In 1998, the Farm Division of the Iowa Attorney General's Office and Iowa State University each issued a news release about micro-nutrient programs (Find copies at www.ag.iastate.edu/aginfo/news/1998releases/micronut.html.) The releases made the following points:

  • Independent research indicates that Iowa farmers seldom need to add micro-nutrients. While future developments in plant genetics and soil fertility may make the application of micro-nutrients cost-effective, in the vast majority of circumstances, Iowa soils naturally contain sufficient levels of these nutrients.
  • Plants that show symptoms of deficiencies can be treated effectively. Micro-nutrient deficiencies that occasionally are verified in Iowa include iron for soybeans, zinc for corn, and boron for alfalfa in dry weather. All can be treated when identified.

The Farm Division makes two observations about the use of micro-nutrients since 1998. First, research conducted by ISU since 1998 verifies earlier data indicating that the use of micro-nutrients is rarely cost effective in Iowa. Second, there has been a significant reduction in the use of micro-nutrients in Iowa. Records from the Iowa Department of Agriculture and Land Stewardship indicate that the use of micro-nutrients has decreased from about 13,000 tons in 1997 to about 4,400 tons in 2001, a decline of 66%. This reduction has saved Iowa farmers an estimated $13.4 million since 1997.

While the Farm Division believes the trend toward less use of micro-nutrients is positive, it renews its advice to farmers that, unless plants show symptoms of deficiency, application of micro-nutrients in Iowa almost never makes economic sense. Farmers who have questions about soil fertility should contact their agronomic service provider or Iowa State University Extension Service at (515)294-1923.


Iowa Attorney General Farm Division
321 East 12th St., Room 018
Des Moines, Iowa 50319
Phone: 515/281-5351
Fax: 515/242-6072
Email: farm@ag.state.ia.us