Zinc is also important to maximize corn yield, Golden says, and producers and consultants should be watchful for signs of zinc deficiency.

“If I told you I could get you 10 bushels more per acre just by applying zinc, I think you would take it. Even with marginal zinc deficiency, it generally pays to apply zinc. In such cases, we routinely found that an over-the-top application could give us on average 10 bushels per acre more.

“At a Bolivar County site, on old rice soil with a pH over 8.0, corn yields in the untreated check were very good — a little over 200 bushels. But where we applied 5 pounds to 7 pounds of zinc, we got an additional 29 bushels. Even though we were already getting a high yield, we were leaving money on the table by not applying zinc.

“On a site at the experiment station, we were cutting 190 bushel corn in the control plot, but where we applied zinc we increased yield by more than 16 bushels.”

Light-textured, low organic matter soils with high pH are where zinc deficiencies are seen most, Golden says, particularly if the field hasn’t had a history of zinc fertilization. “Old, well-watered cotton soils are where we have been observing these problems. With cotton acres declining and a lot of those soils going into corn, that’s where we should look for zinc deficiency.

“Typical zinc deficiency symptoms show up early season, around the V-2 or V-3 growth stage, when corn starts getting stressed in cold, wet soils.

“For years, the best method to alleviate this problem was granular fertilizer, zinc sulfate applied at 10 pounds actual Zn per acre. Producers often object to the cost. But I tell them, ‘It costs money to build up your soil test — you’re investing for the future.’”

When using these granular sources, Golden says, rate should be adjusted based on the water solubility of the zinc source. “With any zinc source, you want the highest water solubility you can get. When you need zinc, you need it right then — not six months down the road. If it has relatively low water solubility, it’s going to take time to break down  for the zinc to become available.”

Fields should be scouted closely at the V-3 to V-4 growth stages to detect zinc deficiency, he says. “If you miss the deficiency signs, then put out your sidedress application and the plants start growing vigorously, you may never know the deficiency was there. But you’ll be hurt on yield at the end of the season. So scout carefully during those early growth stages.”

Many growers have reported leaf burn after spraying over the top with citrate chelated zinc products, Golden says. “In some cases, six days after application we saw up to 65 percent leaf burn. So just be aware, if you use a citrate chelated product, you’re probably going to have some foliage injury.”

But he says, “Even though there was very significant leaf burn from these products,  preliminary results suggest it didn’t adversely affect yield.”

The takeaway message for producers on a corn/soybean rotation, Golden says: Soil sample on a routine basis and follow recommendations to keep soil productivity high.