Properties and Basic Management of Zinc

Zinc has become one of the most commonly applied micronutrients in the Midwest, at least in corn production. Yet over 50% of the soils tested at ALGL are rated as low which is below 3 ppm. Most crops do better with a soil test level around 5 ppm. But as with all micronutrients, adding zinc to your soil is not a replacement for good overall management of your pH and macronutrients.

The role of zinc in plants is to aid protein synthesis, energy production, and growth regulation. As a result, visual symptomology in crop vegetation is not common in most situations. The most common result is a stunted growth which is very difficult visually diagnose, especially when the same symptoms can be caused by a deficiency of several other nutrients. Grass species such as corn and wheat are more likely to show chlorotic deficiency symptoms but can be nearly impossible to discern from other nutrient deficiencies such as manganese and iron. Tissue testing can be a great tool to help determine the culprit.

Zinc deficiencies are common on certain soil types and during certain weather conditions. Soils with high pH, low organic matter, and sandy textures are most prone to low zinc availability. Cold and wet weather conditions lead to zinc deficiencies due to reduced uptake. While there is little to be done about weather conditions, managing zinc inputs on challenging soil types can have a significant impact on overall production. For high pH soils utilize banding placement (2x2), foliar applications, and choose chelated forms of fertilizer. For low organic matter/sandy soils, try to incorporate manure or compost. Adding organic matter to the soil not only brings some zinc with it but also helps maintain the availability of other zinc sources.

Common application rates for zinc are between 2 and 5 pounds per acre in a broadcast application and less than one pound per acre in a foliar application. Fortunately, zinc does not reach toxic levels easily. Elevated zinc levels are common on soil with a long history of manure applications. Especially if the manure comes from older livestock facilities with galvanized floors and pens. Zinc is also very high in manure from hog nursery barns because of the feed supplements used. While there is no definitive soil test level at which zinc becomes toxic, applications should be stopped if the average soil test from a field approaches 10 ppm.