Soil Conditions And The Need For Zinc Fertilizer

Zinc (Zn) is an essential nutrient required in some fertilizer programs for crop production. While some soils are capable of supplying adequate amounts for crop production, addition of zinc fertilizers is needed for others. Research at the University of Minnesota as well as other universities has identified soil conditions where a response to Zn fertilizers might be expected. According to Extension Soil Scientists George Rehm and Michael Schmitt at the University of Minnesota, these conditions are:

• Soil Temperature. Cool soil temperatures in early spring can intensify the need for Zn. When soils are cold, the organic matter does not decompose and Zn is not released and available for crop growth.
• Soil Texture. In Minnesota, most of the response to Zn in a fertilizer program will take place on fine-textured soils. Recent research on sandy soils indicates a response to Zn can occur when high yields are grown on sandy soils with a low organic matter content. The measured response to Zn fertilization in these situations has been small and has not occurred every year. Use the zinc soil test to determine if Zn is needed in a fertilizer program.
• Topsoil Removal. The probability of a response to Zn fertilization increases where topsoil has been removed or eroded away. When soils are eroded, the amount of free calcium carbonate on the soil surface increases. The probability of the need for Zn in a fertilizer program increases as the percentage of free calcium carbonate increases.
• Previous Crop. The probability of a response to Zn fertilization increases if either corn or dry edible beans follows a crop of sugar beets.
• Phosphorus Levels. There is a known relationship between phosphorus (P) and Zn in soils. Excessive applications of phosphate fertilizers have caused a Zn deficiency in corn and reduced yields. In a University of Minnesota study, soil was highly calcareous (pH = 8.3), and the soil test of both P and Zn was very low. A P-induced Zn deficiency is a concern and may occur only if very high rates of phosphate fertilizer (more than 100 lb. P2O5/acre) are used and the soil test for Zn is in the low and very low range. A P-induced Zn deficiency might also be a concern when high rates of manure are applied to crop land. The manure, however, also contains Zn that can be used for crop growth. Therefore, P supplied from manure should not create a Zn deficiency for crop production in Minnesota.