Copper (Cu), a micronutrient essential for crop production, is supplied in adequate amounts by most of Minnesota's agricultural soils. The organic soils are an exception. Past research has shown that addition of this nutrient to a fertilizer program produces substantial increases in yields when small grains are grown on these soils.

More recently, there had been reports that use of Cu fertilizers had increased the yield of hard red spring wheat grown on mineral soils in Canada. After considering the Canadian reports, it seemed that an evaluation of Cu for hard red spring production on the mineral soils of northwestern Minnesota was appropriate.

This evaluation was conducted in the fields of six cooperating growers in 2000 and 2001. The location of the sites and the associated relevant soil properties are summarized in Table 1. Copper was supplied as two sources (chelate, sulfate) to provide 6 and 12 lb. Cu per acre. The Cu fertilizers along with fertilizers to supply adequate N, P₂O₅, and K₂O were broadcast and incorporated before planting. The cooperating farmer planted the wheat. Appropriate herbicides were applied post emergence for weed control. Grain yields were measured with a plot combine. Yields were corrected to 13.5% moisture.

Table 1. Relevant soil properties for the experimental sites used for the evaluation of Cu fertilizers.

Except for the Norman County site in 2000, all soils had an organic matter content greater than 2%. The lower soil test values for Cu were associated with the soils that had the loamy fine sand texture. Grain yields are summarized in Table 2. The effect of only one rate of Cu (12 lb. per acre) is shown.

Table 2. Yield of hard red spring wheat as affected by the application of 12 lb. Cu per acre.

*Treatment means in any row followed by the same letter are not significantly different at the 0.05 confidence level.

In the two years of the evaluation, Cu fertilization produced a significant increase in yield at only one location (Norman, 2000). Both sources of Cu had an equal effect on yield. Yields resulting from the use of 6 lb. Cu per acre were the same as yields produced by the use of 12 lb. Cu per acre.

In evaluating the response to Cu fertilization, it's important to remember that the sandy site in Norman County in 2000 had an organic matter content of less than 2.0%.

The results from this study are consistent with those of similar studies in North Dakota. In those studies, a response to Cu fertilization was only measured where sandy soils had a low organic matter content.

The University of Minnesota recommendations for use of Cu will not change. This micronutrient will be recommended when small grains are grown on organic soils. Those who grown hard red spring wheat on sandy soils with an organic matter content of less than 2% may want to consider the broadcast application of 6 lb. Cu per acre as copper sulfate. There is no firm guarantee that this practice will increase yields.