Does applying Zinc in furrow at planting help increase corn yields?

I think the short answer is maybe but not necessarily profitably. Corn does have a high, critical need for zinc (Zn), and deficiencies can be common, so in-furrow zinc applications might make economical sense in some situations, but there are several factors to keep in mind when deciding what is best for your farm overall.

Testing Soils for Zinc Deficiencies Is Crucial

As a starting point, soil testing should be conducted in order to identify if a zinc deficiency exists.

Jim Camberato and Stephen Maloney of the Agronomy Department at Purdue University explain, “Soil extractants that use chelating agents (DTPA or EDTA) are considered best for detecting inadequate soil Zn levels. However, the critical level for sufficiency is highly dependent on the method utilized. Some laboratories also consider soil pH and P level when estimating Zn availability. Consult your soil testing laboratory guidelines for interpretation of soil Zn levels considered deficient.”

They also add the important reminder, “When sampling soil suspected of low Zn avoid using galvanized metal or rubber which both can contain Zn.”

If you find out that a zinc deficiency does exist, then soil-applied zinc fertilizers can help correct the problem. If a zinc deficiency is not observed, then zinc fertilizer should not be applied.

In-Furrow Fertilizer Placement Has Benefits and Limitations

Agronomist Eric Moore explains, “In-furrow placement is optimal for nutrient availability to newly emerging plants as nutrients are placed in a concentrated band below the soil surface.”

But, he adds this caution, “The limitation of in-furrow, or pop-up fertilizer placement as it is often referred to, is that many of the nutrients are in a salt formulation and can prove to be very toxic to germinating crops. The amount of nutrients that can be safely applied to the seed in-furrow are often far deficient in terms of meeting the nutrient needs of today’s high-yield crops.”

Parenthetically, he also reviews alternative application methods for row-cropping systems including surface broadcast, deep placement, 2” by 2” banding, and zone placement for anyone interested in a quick comparative look at some advantages and disadvantages of various popular options.

Research Trials and On-Farm Observations Show Some Mixed Results

There have been some Extension trials and agribusiness studies that have looked at the effect of in-furrow zinc applications on corn grain yield. Basically, the results have been mixed.

The University of Minnesota conducted multiple relevant research trials. Corn is widely grown in the state and zinc deficiencies can be common so this was a great area for testing. There, a significant yield increase was not observed even when soil tests showed a zinc deficiency to begin with.

“Several research trials were conducted across Minnesota including 1 quart of a 10% fully chelated source of zinc (Table 5). One of the eight sites in the study fell below 0.75 ppm extractable zinc, but corn grain yield did not significantly increase with in-furrow zinc application.”

The Extension nutrient management specialist Dan Kaiser concluded, “We have researched the addition of chelated zinc applied in-furrow as a starter for corn [and] didn’t find it to increase yield in soils that should supply adequate zinc. Thus, we wouldn’t suggest you apply zinc across all corn acres.”

He adds, “It may be a better option to variable-rate apply zinc, targeting field areas testing 0.5 ppm or less with 10 to 15 pounds of available zinc per acre. They can be pretty small pockets of fields, so you have to ask yourself if it’s worth it.”

Regarding corn and in-furrow fertilizer applications, the University of Wisconsin has also conducted various starter fertilizer studies.

Extension corn specialist Joe Lauer has commented, “It's certainly a good practice to get corn off to a good start … . The economics, though, are mixed at best.”