By John Brien, CCA, AgriGold regional agronomist
Zinc is a micronutrient, meaning it is needed in very small amounts by the corn plant. Actually the amount is measured in ounces per acre instead of the normal pounds per acre of other major nutrients such as nitrogen and potassium. A 150-bushel corn crop is known to remove only 0.25 pounds of zinc. Even though zinc is needed in small amounts, it has a huge impact on how a corn plant grows and ultimately how much yield is produced. In a study performed by the University of Nebraska on a low zinc testing soil showed a 53-bushel increase in yield by adding one pound of zinc to a starter.
Zinc plays a critical role in the following systems of a corn plant:
• Aids in the synthesis (production) of growth hormones and proteins.
• It is needed in the production of chlorophyll and carbohydrate metabolism.
• It is essential for the transportation of calcium throughout the corn plant.
• Necessary for cell elongation, the increase in leaf and node size along with grain formation.
Factors that affect zinc availability:
• Soil pH: The availability of zinc decreases as pH increases, the ideal range for availability is a soil pH between 5 and 7. A soil pH above 7 causes zinc to form compounds that are unavailable to plants and thus will show more zinc deficiency symptoms.
• Organic Matter: Zinc is often attached to the soils organic matter and easily accessible by the corn plant. Soils that are low in organic matter have less zinc available and deficiencies are often seen on these soils. Sandy soils and/or highly eroded soils are typically low in organic matter and first to show deficiencies.
• Growing Conditions: Uptake and availability of zinc can be negatively affected by cool, wet and overcast conditions early in the growing season. The temporary deficiency is caused by slow root growth. The slow growing root system is often not able to meet the early season needs of the corn plant. As the temperatures rise and conditions improve, deficiency symptoms should disappear.
• Soil Compaction: Soils that are compacted significantly reduce the corn plants rooting ability. With the lack of roots, the chance of intercepting zinc minerals is reduced and the corn plant is easily put into a zinc deficient state.
• Soil Phosphorus Levels: The uptake of zinc is increased as the soil levels of mycorhizae, a root-associated fungus, increase. When phosphorus levels increase, the mycorhizae population decreases, thus reducing the plants ability to uptake zinc, therefore high soil phosphorus levels tend to reduce the availability of zinc. Phosphorous levels that are higher than 90 lbs/acre are likely to benefit from additional zinc applications.
Zinc deficiency in corn:
The most common symptoms associated with zinc deficiency in corn results in a white or yellow band that runs parallel with the mid rib. Other problems associated with zinc deficiency include:
• Poor root development
• Stunted growth
• Small leaves
• Shortened internodes
• Delayed silking and tasseling
• Chalky kernels.
There is also the hidden deficiency that has no symptoms. Hidden zinc deficiencies are well documented in corn and reductions in yield can be up to 40%. Therefore the best method to determine if zinc is deficient is by taking soil samples to determine the levels of zinc in the soil.
There are typically two methods of applying zinc to a field either by a broadcast application or a banded application done typically at planting. While there are positives to both application methods, the most preferred method of application occurs via banding. Due to the small amounts that are applied, the chances of roots coming into contact with the applied zinc are far greater in a band verse broadcast applications.
Zinc is one of the most important micronutrients for a high yielding corn crop. Through proper soil testing and the willingness to address any deficiencies through proper fertilization, zinc deficiencies can be addressed and corrected. High yielding corn is the goal of every corn grower and zinc could be the missing key to obtaining those yields.