With fertilizer prices on the upswing again, getting the most of every dollar spent on fertilizer is critically important. Two separate, yet related, concepts that can help producers further their fertilizer dollars are foliar feeding and petiole testing.
Glen Harris, University of Georgia Extension soil scientist, presented a research paper at the recent Beltwide Cotton Conferences on foliar feeding and the petiole testing program.
General Guidelines For Foliar Feeding
• Supplemental to a good soil-applied
• Not all nutrients foliar feed well
• Low volume needed; not pivot feeding
• Don’t foliar feed a stressed crop
• Need best determined by tissue or
When to use petiole testing
• New grower
• New ground
• With organic amendments
• New fertilizer formulations
• New varieties
Harris says that foliar feeding is somewhat controversial in the subject of soil fertility because it seems that people either love it or hate it.
“I have talked to people that say, ‘You don’t need to put anything on the soil; just feed it all through the leaf’,” he says. “And then, on the other hand, there are people who say foliar feeding doesn’t work; you can’t get nutrients through the leaf.’”
A Place For Foliar Feeding
Harris says he falls somewhere in the middle. He thinks foliar feeding has a place, but it doesn’t work all of the time and, therefore, you can’t rely on it totally.
“Where it really works is when you are on what I call the ‘bubble of sufficiency,’” he says. “Where you are very close to having what you need, but you do need a little more to get you there.”
Harris says that although foliar feeding is not right for every producer or in every state, producers who do use this option should plan to foliar feed during the peak bloom period.
Foliar feeding is supplemental to a good soil program.
“Not all nutrients foliar feed well,” he says. “For example, with phosphorus we don’t tend to get a response.”
Of the secondary nutrients, he says magnesium does foliar feed well, but it is rarely deficient.
“The micronutrients manganese, boron and zinc all foliar feed well,” he says. “And luckily they do because these are the ones that we are most likely to have problems with on Georgia cotton if we have problems with any micronutrients.”
Pivots Not Low Volume
For foliar feeding, ground rigs are used, applying only 10 to 15 gallons per acre, according to Harris.
“Low volume is what you need to get it on the leaf and keep it there,” he says. “It is amazing to me that some producers still think that distributing the nutrients through the pivot is foliar feeding.
“We have growers putting 30 pounds of nitrogen through the pivots, and I guess they see it hitting the leaves, and they think it’s going through. But, when you think about it, most of the nutrients are hitting the ground.”
Harris says planes apply only three to five gallons per acre, and it is trickier to get a lot of nutrients on without a burn situation.
Why Test The Petiole?
What’s the best way to tell if you need to foliar feed additional nutrients to the crop?
“Petiole testing,” Harris says. “That’s where petiole testing comes into play.”
He says the University of Georgia petiole testing is a complex program.
“You buy one kit per field for $50, and you get 10 envelopes for the 10-week program,” he says.
Starting the week before bloom, Harris says you take 30 petioles from throughout the field as a representative sample. Along with the petiole samples, a card indicating the sampling date, moisture level, insect control used, fruiting and stalk size is submitted. What is returned is a chart that shows whether the sample is within the adequate range for nitrogen and potassium, plus specific recommendations are made for the crop. For the recommendations, urea is used for the nitrogen material and potassium nitrate for potassium.
Petiole Testing Vs. Tissue Sampling
A point to clarify, Harris says, is that there is a difference between petiole testing and tissue sampling.
“Tissue testing is taking the leaf blade, and we run total nitrogen, phosphorus and potassium, as well as other nutrients,” he says. “Tissue sampling is recommended between first square and first bloom, and we have sufficiency ranges for those nutrients during that time period.
“The petiole program is different. Petiole testing starts at first bloom and goes for eight weeks. When you send in the stems, we test for nitrate nitrogen and we run phosphorus and potassium levels, and the phosphorus is mainly to see how it interacts with the nitrogen.
Harris says the petiole testing system is very fine-tuned at predicting nitrogen and potash deficiencies coming on and helping you correct them.
Deficiencies Can Look Similar
Harris says petiole testing is a good tool for farmers to use when an organic amendment, such as chicken litter, is being used.
“It’s an organic source, but availability of nutrients is not very predictable with chicken litter,” he says. “That’s where petiole testing can come in handy – to really tell how much nitrogen you are getting from the litter and if you need to supplement or not.”
Harris also says that with the use of urease inhibitors and nitrification inhibitors how the plant takes up nitrogen can be changed, and petiole testing can serve as a guide to find out how much nitrogen you are actually getting into the plant.
While advanced sensor technology may replace the need for petiole testing one day, there are still questions to be resolved.
“Both nitrogen deficiency and potash deficiency both turn the plant yellow,” says Harris. “I don’t know if we have figured out how the sensor will determine between the two.”
Overall, Harris says the petiole testing program is not being used to its potential in Georgia, and there are likely several reasons for this.
“I think it has to do with the complexity of the program and maybe cost, also less use of scouts,” he says.
Harris says he hopes to be able to change the program in the next year or two to remove some of the complexity so that it can be used more.
“Petiole testing is a great way to determine foliar feeding,” he adds. “We are just not using it.”
Contact Amanda Huber at (352) 486-7006 or firstname.lastname@example.org.