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Fertility Management

A nitrogen-to-sulfur ratio (N:S) that is too high can cause yellowing of corn seedlings. Although a certain amount of sulfur is needed for the nitrogen to work properly in the plant, the ratio, according to a tissue sample report, should be less than 16:1.

Soil fertility levels, yield goals, weather and placement all play a part in nutrient uptake.

Producers understand the judicious use of fertilizer. Too much or too little can have catastrophic effects on the crop and on the wallet as well. Fertilizer recommendations depend on the soil fertility level as determined by soil tests and the yield goal, but keep in mind those factors that may affect nutrient uptake, such as weather and placement.

Glen Harris, University of Georgia Extension agronomist and soil fertility specialist, says fertilization programs not based on soil tests may result in excessive and/or sub-optimum rates of nutrients being applied.

“Take soil samples each fall to monitor the current fertility level. Use the yield goal to determine the quantity of nitrogen, phosphate and potash to be used,” he says. “At high-yield levels, the balance of nutrients in relation to one another is also important.”

High Yields Depend On Many Factors
When planning fertilizer usage, Harris urges producers to be reasonable in their expectations and projections.

“In 2013, I purposely fertilized some corn plots to try to achieve 150, 200 and 250 bushels per acre. I was dead on up to the 300-bushel level where I only made 270 bushels,” he says. “The point is, if you fertilize for 300 bushels and you only make 250, then you lose money. Likewise, if you fertilize for 200 and could have made 250,
then you lose money too, or the opportunity to make more money.

“If you haven’t come close to making 300 bushels per acre, then you probably shouldn’t fertilize for that. If you are coming close to making that yield and want to go for it, then that’s your option.”

Harris adds that he has yet to make 300 bushels per acre in his corn plots.

“It was close at 270, and I think I had enough nutrients to make 300. It was probably a combination of row spacing, plant population, weather and lack of a good way to spray fungicides that limited yield.”

Find The Right Place For Starter Fertilizer

Questions about the use of starter fertilizer are something producers ask a lot, says Harris. But, he says he doesn’t like putting starter fertilizer in the furrow because of the risk of seedling mortality.

“I actually killed some corn from overdoing it in the furrow,” he says. “I have data that shows by the time you have lowered the rate in-furrow so that it doesn’t hurt the seedlings, it also doesn’t help the seedlings.”

Rome Ethredge, Seminole County Extension director, says he uses the two-by-two method. On the corn-planting rig, a set of round coulters sits out in front of the set where the seeds are coming out.

“That front set of coulters go into the soil about two inches deeper than the seed will be placed and about two inches to one side,” Ethredge says. “There is a tube inside the coulters that pours out liquid fertilizer we call ‘pop up.’ The placement is so that the young seedling will get it very quickly. But we don’t put it right in the seed furrow so as not to burn the seedling with the strong fertilizer.

“This is the preferred two-by-two starter fertilizer placement for field corn,” he says. “Usually, it is mostly phosphorus with some nitrogen. Phosphorus is important for young seedlings, especially with cool soils.”

Weather Plays A Leading Role In Nutrient Availability

Seedlings are not very different than many humans: On cold, wet days, it can be difficult to get going.

Ethredge says it is harder for plants to take up phosphorus in cool conditions, and especially where pop-up fertilizers are not used phosphorus deficiency is more likely to be found.

“Cold, wet soils also delay the release of sulfur from organic matter,” he says. “Sulfur is a nutrient that is not needed in great amounts, but is needed by plants, especially corn.”

Harris says the sulfur deficiency last year didn’t surprise him given the rainy spring.

“I expected the weather would make it worse. Sulfur is leachable, and the roots tend to struggle for a while when sulfur is less available. That’s why I like to put some out at planting and also at sidedress.”

While weather is not something producers can control, soil pH is, and nutrient availability is very dependent on pH level.

Magnesium is more available to plants at higher pH, and zinc is more available at lower pH levels. Harris says corn grows best in soils with a pH of 6.0 to 6.5.

“Over-liming may actually cause zinc problems in corn,” Ethredge says. “I saw a case where it was new ground and they had burned old trees and brush and then limed the field well. Where these burn piles were, zinc deficiency was found.”

Remember, soil from under a burn pile will often have a higher pH. “A foliar spray or two of zinc will often rectify the problem,” he says.

Soil Preparation Reminders

A good soil management program:

  • protects the soil from water and wind erosion.
  •  provides a good, weed-free seedbed for planting.
  •  destroys hardpans or compacted layers that may limit root development. To conserve moisture and reduce compaction, work the land no more than necessary to achieve these objectives.
  • Water erosion is a significant problem on many Georgia soils during high rainfall winter months. Wind erosion can be a problem on sandy Coastal Plain soils in early spring when blowing sand can severely injure young corn plants. Crop residue left on the soil surface or a seeded cover crop effectively reduces water erosion problems. Using minimum-till planting practices such as strip-till or slit-till helps reduce soil losses and “sand blasting” from wind erosion.

From the University of Georgia’s Corn Production Guide, section titled “Agronomic Practices For Corn” by Dewey Lee, Extension agronomist.

Thinking Of Using Poultry Litter?

Here Are Some Stats:
• On average, poultry litter contains 60 pounds of nitrogen, 78 pounds of phosphorous and 56 pounds of potassium per ton.
• Poultry litter has a computed fertilizer value in excess of $80 per ton.
• Poultry litter has practical value to a variety of crop producers.
• Fifty percent of crop producers in South Georgia use poultry litter; 24 percent use it as their only source of fertilizer.
• Most crop producers use poultry litter at a rate of two-tons per acre.
• Crop producers spend a substantial amount of money on inorganic fertilizers each year, with more than half of those surveyed spending $600 to $1,000 per ton per year.
• Crop producers apply fertilizer to large acreages each year, the cost of which varies based on the type of fertilizer.
• With only about 50 percent of producers using poultry litter, opportunities exist for more applications. The lack of more widespread use could be a result of unavailability of litter or the lack of information on the value of poultry litter as a fertilizer.
• Approximately 45 percent of respondents indicated that applying poultry litter improved yield.
• Crop producers utilizing litter indicated a willingness to travel significant distances to obtain it.
• The percentage of complaints from neighbors indicate the need for establishment and use of best management practices for poultry litter application.

From “The Value of Poultry Litter in South Georgia,” by Claudia S. Dunkley, Extension Poultry Scientist, UGA Department of Poultry Science, Dan L. Cunningham, Extension Poultry Scientist, UGA Department of Poultry Science and Glendon H. Harris, Extension Soil Scientist, UGA Department of Crop and Soil Sciences.