As corn yields continue to climb, more micronutrients are removed from the soil. Depending on the type and pH levels of their soils, growers may be prevented from realizing optimal yield potential due to a micronutrient deficiency.
You have heard of “The Magnificent Seven?” Well, in corn there is the Micronutrient Seven: boron, chlorine, copper, iron, manganese, molybdenum and zinc. High pH soils, sandy soils and soils with low organic matter may make some of these micronutrients less available and, therefore, deficient, says Steve Butzen, agronomy information manager, DuPont Pioneer.
By the time symptoms show up in the field, it is often too late to manage the deficiency. Therefore, agronomists generally recommend soil and plant tissue tests. The most reliable micronutrient soil tests are for zinc, boron, copper and manganese, Butzen says. Samples should be taken from the root zone from 0 to 8 in. deep.
Plant tissue analysis is recommended when reliable soil tests are unavailable. It also is considered a good supplement to soil testing. University extension specialists recommend using locally calibrated fertilizer recommendations based on soil test results.
Growers who determine they have a micronutrient deficiency can choose among inorganic, synthetic chelates and natural organic fertilizers. Inorganics include oxides, carbonates, sulfates, chlorides and nitrates. Synthetic chelates, such as Zn-EDTA, are considered more effective in correcting zinc deficiency than other forms of applied zinc. Natural organic complexes include lignosulfates, phenols and polyflavonoids.
Tim Maloney, Agri-Tech Consulting, Whitewater, Wis., has evaluated micronutrient treatments on corn for several years — some foliar applications and some seed treatments. In corn, he has focused mostly on zinc and sulfur (considered a secondary nutrient in corn).
In Roundup Ready corn, Maloney has applied these treatments with glyphosate at plant stages V4 to V6 to coordinate with postemergent herbicide applications. He also has applied the micronutrient treatments at the R1/R2 stage in corn to complement foliar fungicide applications. In addition to the micronutrients, Maloney will typically include macronutrients (nitrogen, phosphorus and potassium).
The crop consultant has observed the greatest visual improvement after early micronutrient fertilizer applications (at the V4 to V6 stage). “Improved tissue color, vigor and plant health are typical with the micronutrients, especially zinc in corn,” Maloney says. The applications have increased the root mass of corn plants as well. “Probably more important is yield,” Maloney says. “For corn, zinc application has improved yield by 3 to 5 bu./acre.
Maloney has tested micronutrient fertilizer treatments from Precision Laboratories, UAP/Loveland, BioTech Nutrients, AgXplore International and The Andersons.