Can You Afford Not to Apply Zinc This Year?

Currently, we are several weeks out until spring crops will be planted. Even though the present grain value of some crops is less than in previous years, you must keep in mind that in order to raise a bushel of corn, soybeans (or any other crop), the plants still require a certain, specific quantity of each nutrient to raise that bushel “regardless of the price!" If you omit any critical nutrient input, you likely will produce a lower yield – this certainly holds true for zinc. Crops most responsive to zinc applications include corn and edible beans, followed by moderate responses in wheat, soybeans, potatoes and sugarbeets.

Of all the essential micronutrients, zinc is the most commonly applied. It is multi-functional in plant nutrition, catalyzing growth hormone function in early shoot and root growth and development. It helps facilitate chlorophyll production, necessary for regulation of sugar consumption, and is essential for seed initiation/formation and in the maturation processes. Interacting with all of these functions, zinc also plays a positive role in efficient use of phosphorous. Where zinc is properly utilized, crop responses will exhibit earlier maturity, increase in seed test weight, and decrease in percent moisture at harvest, along with positive yield responses.

Important interactions that may affect zinc responses can include the following:

1. Low zinc soil tests. Optimum zinc soil test levels are 2.5-3.0 ppm ( DTPA extractable).
2. Heavy applications of phosphate fertilizers or manures, or high phosphate testing soils. Banding phosphorus via starters and/or strip till applications can induce a zinc deficiency, especially if the zinc soil test is medium or lower.
3. High nitrogen and potassium fertilization/soil test levels may interfere with zinc availability.
4. As soil pH increases above 6.8, zinc solubility (availability) decreases dramatically. Fertilizer zinc is optimized when fertilizer reaction pH is managed to be in the pH range of 5.0 -6.0.
5. Cold/cool soil temperatures will limit zinc diffusion and adsorption into the root system. A California study demonstrated that as soil temperature increased from 55 degrees to 75 degrees, zinc availability increased by a factor of 5. This fact supports many positive, early season responses to zinc when applied in a starter band or as a seed treatment, even in soils testing adequate in zinc.

The keys to attaining good crop responses to zinc are placement (optimizing access), maintaining solubility for crop utilization, and timing. Placement of zinc should be made to optimize root adsorption early in the season. Starters, either in-furrow or a 2 x 2, and/or zinc seed treatments accomplish optimum zinc placement and timing. Your main goal with zinc applications should be to place the zinc where it will best optimize root growth.

Crop availability of zinc is also dependent on the zinc being soluble (available) for adsorption and eventual utilization (translocation). A zinc source and rate study conducted by the Fertilizer Development Center (TVA) showed that organic acids combined with zinc improved zinc uptake and yields in corn on par with more expensive inorganic chelates (EDTA). Additionally, the more water soluble the zinc source, the better the zinc response. Helena has some excellent, cost effective choices to provide zinc in a stable, available form to your crops and promote root growth.

- Sam N. Bartee, CCA/CAC, West Central Division Agronomist