Micronutrients are required in small amounts for normal plant growth. The level of each micronutrient in a soil is controlled by many factors. Some of these factors include soil geology and formation, annual precipitation, crop removal, soil erosion or deposition, etc. To learn more about the level of micronutrients and secondary nutrients in the soils of our region, we have summarized soil test results from 1999. In addition, we summarized the level of organic matter, potassium, phosphorus and soil pH. Soil organic matter contributes substantial amounts of secondary and micronutrients as it is broken down by microorganisms (i.e. sulfur, zinc, boron, etc.). You can see when you compare the organic matter and boron figures that areas where most of the soils are low in organic matter (i.e. Western North Dakota) most of the soils are also low in boron. Soil pH also influences the level of micronutrients in the soil by affecting their solubility. As the soil pH increases, the solubility of many micronutrients decreases. One example of this can be observed when comparing the zinc and the soil pH figures. Along the southern border of Minnesota, where only 15%-18% of the soils have a pH >7.3, most of the soil samples are higher than 1.0 ppm zinc.

These regional micronutrient summaries should be used in educating growers about the possibility of a micronutrient deficiency in their area. They should not be used to make micronutrient recommendations on individual fields. While micronutrient soil tests are a valuable management tool, there is limited university research on crop responses to micronutrient fertilizer in many areas. Plant tissue testing should be used in addition to a soil test to confirm a micronutrient deficiency.

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