Michigan State University Extension
Soils & Soil Management - Fertilizer - 05209707
07/10/97
Secondary and Micronutrients for Vegetables and Field Crops Extension Bulletin E-486, Revised August 1994
By M.L. Vitosh, D.D. Warncke and R.E. Lucas Department of Crop and Soil Sciences Michigan State University Extension
Copper is essential for plant growth and activation of many enzymes. A copper deficiency interferes with protein synthesis and causes a buildup of soluble nitrogen compounds.
Normal plants contain 8 to 20 ppm copper; deficient plants usually contain less than 6 ppm. Each ton of dry hay contains about 0.002 pounds of copper.
Without copper all crops fail to grow. Fortunately, most Michigan soils have sufficient copper. Peaty soils, which have a low ash content, are generally the only soils deficient in copper. If the problem does appear on mineral soils, it will most likely be on acid soils that have been heavily cropped but well fertilized with N, P and K. Copper applied to soil is not easily leached; nor is it extensively used by the crop. Consequently, no further copper fertilization is needed on organic soils if a total of 20 pounds per acre has been applied for low responsive crops and 40 pounds per acre for highly responsive crops.
Copper Deficiency Symptoms
Copper deficiency in many plants shows up as wilting or lack of turgor and development of a bluish green tint before leaf tips become chlorotic and die (Vis. 23), (Vis. 24), (Vis. 25). In grains, the leaves are yellowish and the leaf tips look frost damaged. Carrot roots, wheat grain and onion bulbs show poor pigmentation. (Vis. 6) shows the relative crop response o copper fertilizer. Alfalfa, lettuce, oats, onion, spinach, Sudan grass, table beet and wheat are the most responsive crops on organic soils.
Correcting Copper Deficiency
Application rates for organic soils based on soil tests are given in MSU Extension Bulletin E-550B. Rates of copper commonly used in highly responsive crops are 3 to 6 pounds per acre, depending on the soil test level. These rates should be doubled on fields that have never received copper.
Common carriers of copper are the sulfate and the oxide. Copper sulfate is blue and easily identified in most fertilizers. It has a copper concentration of 22.5 percent. Copper oxide, a brown material, has a copper concentration of 60 to 80 percent. In field tests, this material has been as effective as copper sulfate.
Copper Toxicity
Excessive soil copper levels have not been a problem in crop production. However, the potential for copper toxicity does exist because copper is applied annually for some vegetables, either as a soil amendment or a component of some fungicides. Copper toxicity often results in plant stunting, a bluish tint to leaf color, and leaf cupping followed by chlorosis or necrosis. When the copper concentration exceeds 150 ppm in mature leaf tissue, toxicity may occur. Cumulative copper applications of 100 pounds per acre have reduced cucumber and snap bean yields on sandy soils.
Copper is tightly adsorbed by most soils and will not leach. Therefore, once a copper toxicity problem develops, it may be very difficult, if not impossible, to alleviate it.
| Visual title - Visual size | Visual title - Visual size |
|---|---|
| Copper-deficient onion - 13K | Copper-deficient Sudangrass - 17K |
| Copper-deficient corn - 29K | Relative response of crops to micronutrient fertilizers - 78K |
