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Cotton fertilization hot topic at Expo Field Day

Cotton fertilization hot topic at Expo Field Day
• There’s a lot of late-planted June cotton in Georgia, and there are several key points that should be remembered when adjusting to this situation.

One of the driest springs on record continues to perplex cotton producers in the lower Southeast as they enter the mid-season mark with many questions about how to handle fertilization of the 2011 crop.

“With the drought this year, we have a lot of late-planted cotton with uneven stands,” says Glen Harris, University of Georgia Extension soil scientist. “We’re getting a lot of questions about how to fertilize with nitrogen when you’ve got skippy stands or non-uniform plant stands.

“I’d say when the older cotton gets ready, I might go ahead and pull the trigger because that might be the cotton that does best for you. The only way you can hurt really small cotton with nitrogen is if you dribble right onto it and burn it.”

Harris was one of the featured speakers during the recent Sunbelt Agricultural Expo Field Day, held in Moultrie, Ga. Those attending this year’s event got the opportunity to see about 200 acres of cotton and the latest in varieties from Deltapine, Bayer, Americot and Dow, in addition to the latest research from the University of Georgia’s Extension Cotton Team.

Harris says his work at Expo is focused on potassium nutrition and its interaction with new cotton varieties. “Newer varieties do need a fair bit of potassium, and we’ve had our share of potassium problems. I’ve shifted the emphasis this year to how some of these new varieties might respond to some of the things we’re doing with potassium. We’re splitting applications, foliar-feeding potassium, and foliar-feeding early and late,” he says.

Turning to current crop conditions, Harris says there’s a lot of late-planted June cotton in Georgia, and there are several key points that should be remembered when adjusting to this situation.

Growers shouldn’t try to rush the crop by over-fertilizing with nitrogen, says Harris.

“Unfortunately you cannot fertilize your way out of a drought. I wish you could. And in fact, trying to rush a late-planted crop with extra nitrogen can actually backfire and delay maturity making matters even worse,” he says.

Harris advises producers to go with conservative side-dress nitrogen rates on dryland (50 to 60 pounds per acre depending on how much preplant nitrogen was applied) according to yield goals.

“If the rain situation improves as the crop progresses, you can always make up some ground with foliar — up to 20 pounds per acre if you use feed grade urea and are willing to foliar feed more than once.”

Side-dress nitrogen should be applied early, he says. The normal “window” for side-dressing nitrogen is from first square to first bloom.

Hedge toward first square

“For late-planted cotton, especially dryland, you may want to hedge more toward first square than first bloom. Unfortunately, many preplant nitrogen applications were skipped and side-dress is the first nitrogen fertilizer the cotton plant is receiving. Again, be cautious about applying too much nitrogen to late-planted cotton too early.”

While it is true that most new cotton varieties fruit up earlier, and it makes sense they would need nitrogen earlier, there is also the strong possibility that you could interfere with the plant wanting to shift from vegetative mode to reproductive mode, says Harris.

That is, making it want to keep growing stalk instead of shifting to putting on bolls. On late-planted cotton, growers have less time to make the crop and usually cannot afford this delay.

On uneven stands, producers should fertilize to the majority and hopefully the oldest, he says.

“I’ve seen a lot of fields, again dryland, where some cotton had enough moisture to come up early, but then another ‘flush’ came up much later. It is not uncommon to have cotton plants that are near first square and others that have just emerged in the same field.

“The rule of thumb should be to time your side-dress nitrogen application according to which stage you have the most of in the field.

“This recommendation is easy to follow when you have mostly older cotton, but is much trickier when you have ‘half and half,’ especially if the tall cotton and short cotton are randomly mixed together and not in large patches.

“The only danger of side-dressing really young cotton is if you use liquid nitrogen and dribble a full rate directly on top or into the terminal. There is also a possibility of you side-dressing nitrogen close to very young cotton and if it turns dry, you could get some salt injury.”

Foliar nitrogen and potassium can help “get you through,” but they won’t do it all, says Harris. Foliar feeding nitrogen and potassium always should be seen as a way to supplement a good soil-applied fertilizer program.

“In times of limited soil moisture, it can be a good way to get some nutrients into the plant when the plant may be struggling to take up nutrients through the roots. We have seen this, especially with potassium, on Georgia cotton before, where soil potassium levels are adequate, but due to dry soil conditions, the plant goes almost deficient during droughts.”

Are limits to practice

There are limits, he adds, and it is not recommended to foliar feed anything if the crop is drought-stressed to the point to where it is “wilted by noon.”

“Also, it may be tempting to try to foliar-feed nitrogen instead of side-dressing until you see there is some true yield potential on drought-stressed dryland. However, this is not recommended. If a dryland crop is ready to side-dress, i.e. at first square, I would recommend side-dressing nitrogen over foliar feeding.”

Also at the field day, Guy Collins, University of Georgia Extension cotton agronomist, said he is looking at PGR strategies for newer varieties.

“When we lost DPL 555, we lost our staple variety, but we also lost our PGR management style for that particular variety,” says Collins.

“As you know, DPL 555 was a very aggressive variety in terms of its growth habits, especially in irrigated fields. It required a fairly aggressive pre-bloom application and several other PGR applications.”

Many new varieties today don’t need as aggressive PGR management, as growers learned last year, he says.

“We’ve got several trials this year looking at the response of some of these new varieties to PGR strategies. Looking at highlights from last year’s research, if you look at individual boll contribution to overall yields, Phytogen 565 has the closest boll distribution to DPL 555.

“But 565 really responds to PGR  management. Some of the other varieties like FiberMax 1740 and Stoneville 4288 are good varieties in the appropriate environment, but they’re very early maturing and cut out very quickly. DPL 1050 and 1048 tend to be more aggressive varieties in dryland or irrigation situations,” says Collins.

There’s still a learning curve involved in gauging the response of new cotton varieties to PGR, he says. “A lot of these varieties don’t need that pre-bloom application like we used with 555, but we do need to pay more attention to overall growth of these new varieties throughout the season. We don’t need to use a one-size-fits-all approach.”

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