Micronutrients can become a limiting factor to achieving good yields.
By Amanda Huber
Now that producers have a good handle on the primary and secondary nutrient needs of peanut, soil scientists have shifted focus slightly to include work on micronutrients.
When producers think of the essential plant nutrients, it is the primary nutrients of nitrogen, phosphorus and potassium that come to mind first, even though it’s carbon, hydrogen and oxygen that are present in the plant most with carbon making up 40 to 50 percent of the plant’s dry weight matter.
“In thinking specifically about peanuts, it is a legume and able to fix nitrogen from the air and convert it to a form usable to the plant,” says Glen Harris, University of Georgia Extension soil scientist. “They are also good scavengers of phosphorus and potassium.”
Calcium Still Essential
The next most essential element becomes calcium, and that’s why it became more of a focus when larger-seeded varieties, which had kernels more the size of Virginia type than the older type runner varieties, came about.
“We were concerned that it would cause pops and pod rot,” Harris says. He and others found that no more calcium was needed compared to the smaller seed, but the absence of the required amount would show up more often in the larger-seeded crop.
Harris says producers should take a pegging soil sample, which is taken about 3 inches deep, next to the peanut row soon after emergence. If the sample shows at least 500 pounds per acre of soil-test calcium and if the calcium to potassium ratio is 3:1 or better, then calcium is sufficient and the producer does not need to apply gypsum. If one of these requirements is not met, apply 1,000 pounds per acre of gypsum at early bloom. All peanuts grown for seed should automatically receive this gypsum application regardless of soil test calcium levels.
For the other secondary nutrients, magnesium can be found in dolomitic lime, and some sulfur is available in gypsum.
Know Your Micronutrients
Beyond the primary and secondary nutrients, the first micronutrient in order of importance is boron, says Harris. The University of Georgia has an automatic recommendation of one-half pound of boron on peanuts.
“Boron is important for pollination and fruiting, and, therefore, it is important to have it out before flowering and fruiting and can be applied in an early fungicide spray,” he says.
Manganese is the next micronutrient of importance and is very tied to soil pH, Harris says. “Producers often see manganese deficiency on the edge of the field where they had a lime pile, but there can be manganese deficiency throughout the field. Essentially, the higher you raise your pH, the more you need manganese in your soil.
“Manganese deficiency needs to be caught early. Look at your soil samples now with your county agent. He or she can help you determine, ‘Yes, you are going to need some manganese in this field, and this field should be fine.’”
Too Much Of A Good Thing
The next essential micronutrient, zinc, is a special case. Harris says peanuts are actually sensitive to zinc and can encounter zinc toxicity.
“You can have a zinc level around 10, just keep your pH above 6.2,” he says. “You can even have zinc around 40, and it’s fine if you keep the pH up around 6.6. But, I’ve had someone say they had a zinc level of 100 and I said, ‘You’re on your own.’ I probably would not plant peanuts in that case no matter what the pH was.”
If you apply chicken litter, Harris says it can contain on average about a half-pound of zinc per ton, but it also helps maintain a good soil pH because it has some lime in it.
Other micronutrient deficiencies are rare, but Harris will be looking at copper this year because there are some people applying a copper nutrient. Nickle is also now considered an essential micronutrient, but what does it do in peanuts? That’s something Harris says he and Julie Howe, Auburn University soil scientist, will be studying in research trials this year.
Do The Math On Rates
Another thing about micronutrients is that they have a narrow window of sufficiency, Harris says. “You say, ‘Well, I don’t have enough micronutrients, so I’ll just pour a bunch on there.’ Unlike other nutrients, micronutrients have a narrow window of sufficiency. If you go beyond that sufficiency range, you get into toxicity. You have to be careful in that regard.”
Harris also cautions producers on sales pitches of products and to really do the math on rates. “Sometimes they won’t tell you the actual rate of boron. They’ll say, ‘Six ounces of a five percent boron material,’ and if you do the math, you’ll find that’s a rate of .025 pounds boron per acre, well below our recommended rate of a half-pound of boron per acre. It might work for you, but more likely than not, it won’t.”
How To Avoid Micronutrient Problems In Peanut
1. Study soil samples and look for manganese and zinc versus pH relationship.
2. Grid sample and use variable-rate lime where needed.
3. Apply full recommendation of boron on a timely basis.
4. Soil and tissue sample early if problems are suspected.
5. Follow Plant Analysis Handbook for recommendations for foliar feeding.
