What is in this article?:
- It's never too early to start considering the factors that dictate the use of plant growth regulators in cotton.
- Past research has shown that there's no interaction between plant growth regulator and nitrogen application strategies on yield and fiber quality.
KNOWING THE AGGRESSIVENESS of your cotton variety and environmental conditions during the production season are important in making plant growth regulator application decisions.
No correlation to fiber quality
Researchers cannot find a consistent correlation between PGR use and fiber quality, according to Monks.
“Our study showed that there’s no way to know if it makes fiber quality better or worse. The one thing that has the greatest effect on fiber quality is variety. Fiber quality is inherent to the individual variety, and and yield is a combination of variety and environment. So it’s the genetics in the plant and the environment during the growing season.”
The fact that cotton is a perennial makes it difficult to predict what the plant will do, he says – it’s blooming, growing and laying down fiber quality and yield all at the same time.
Up until the time cotton reaches square, the demand for nitrogen is fairly low, says Monks. “We put out a low rate of nitrogen when we plant the crop to carry us through that time, and then sometime before it blooms, we’ll put on our sidedress. Nitrogen rates usually fall somewhere between 90 and 120 pounds, and, more than likely, are split into two applications.”
Fertilization rates and timing can vary by region, he says. “In the Wiregrass region of southeast Alabama, we’ve said you can wait until first bloom, but you want to put out a sidedress of potash and nitrogen at the same time, you’ve waited too late because nitrogen will get into the root system, but potassium is not moving much. The only way to get it out and into the root system is to put it out a little earlier.”
Generally speaking, if you plant on May 1 in Alabama, you’ll see the first white bloom on July 1, says Monks.
When nitrogen demand peaks
Sometime in late July or the first part of August, the demand for nitrogen from the cotton plant is at its highest. When cotton is at its peak demand, the root system starts aging out for that year. The cotton plant is designed to live for years in the right environment. It’s blooming, fiber is making, yield is making, and quality is making all at the same time.”
Growers have to think of their nitrogen applications separately from their PGR applications. “Where the two are connected is that every variety has its own aggressive tendencies,” says Monks. “Some are more aggressive vegetatively than others. We had a variety a few years ago that if you put on 4 ounces of PGR at match-head square, it was almost too short to pick by the end of the season. That variety was extremely sensitive.
“Other varieties are inherently aggressive, and it’s important to take note of this before or as the season starts so we’ll know if we need to start multiple PGR applications early – do we need to start before first bloom at pinhead or matchhead square and slowly load the plant.”
Concerns about nitrogen application enter the picture when a grower has poultry litter in the field and then adds additional nitrogen, says Monks.
“So chicken litter is being releasing N, we’ve got half a load of nitrogen in the field, and the cotton is growing like crazy. That’s when we start looking at the plant and making those PGR applications based on what the plant is doing.”
Foliar N applications, says Monks, probably won’t do much to push cotton. “The leaves aren’t really made to take up nitrogen – the roots are. We can possibly carry the crop a little bit longer and put on a few more bolls. But we can’t make a crop of cotton with only foliar applications unless we want to be out in the field every two to three days.”