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Cotton enters final stages of season

Standing in a well-tended, central Arkansas cotton field, Leo Espinoza yanks a plant from the soil. Upon inspection, he furrows his brow and points to widely spaced nodes. He turns the plant over and studies a sparse web of roots.

“We're seeing this all over the state. The rains this season have affected our crop badly and in many ways. Anytime we have an abnormal rainfall pattern it interferes with our ability to control fertilization and other things in cotton. This,” says the Arkansas Extension soil specialist while holding the plant up, “is what can happen.”

Rains and fertility

The excessive rains in Arkansas, as in neighboring Delta states, haven't been kind. Many of the state's cotton producers, as late as the first week of July, still hadn't applied nitrogen fertilizer. Farmers who split their fertilizer often were unable to apply the second shot. Fields were just too wet.

Generally, the earlier the cotton was planted, the better it appears. Problem fields usually hold late cotton — planted in the second half of May or later.

“We've been getting many calls about this,” says Espinoza. “Unfortunately, there is no blanket recommendation. (Extension cotton specialist) Bill Robertson and I have been telling producers that they should fertilize on the basis of yield potential and growth stage of the crop.

“For instance, this crop has seven nodes above white flower. When the white flower is at the fifth node, the plant has reached physiological maturity. So, this plant, at the least, has two more nodes to go. If this crop is short of nitrogen, there's still a little time to put out some fertilizer. There will be few fields where a dry fertilizer will be beneficial. However, assuming there's a good yield potential, it's likely that a foliar application would work best.”

“Some producers got nitrogen out before the latest rains,” says Robertson. “That cotton, especially in the central and northern parts of the state, looks really good. But in cotton where no nitrogen — or only the first split — was put on, we've got questions and concerns.”

This year, Robertson says, it's common to see nitrogen-deficient plants as well as sulfur deficiencies. It's interesting, he notes, that cotton petiole samples back from the lab often show nitrate levels are “out the roof” while sulfur levels are very low.

Fertilize or not?

For yield, the first shot of fertilizer isn't the biggest concern. Normally, Extension recommends fertilization be split with a third to a half applied at planting. The balance should be applied some 30 to 35 days later.

“Regardless, if they miss the first shot, the plants may be stressed, but they can recover,” says Espinoza. “Yield potential can be severely affected if the second shot is missed.”

There is a caveat: don't apply too much. If a producer missed the first application, Espinoza recommends a conservative approach to the second — just stick with the original plan.

“If a producer normally applies 100 pounds in 50/50 shots, then don't put out the whole 100 pounds on the back end. Just stick with 50 pounds. If you go with the full amount, it's a waste of money. Fertilizer will be lost because fruits have a limited ability to use the nutrients. You may have a gorgeous, green canopy, but the bolls aren't being helped much.”

Robertson elaborates: “When you put a foliar feed on and it greens the crop up, that foliar feed wasn't needed. The bolls are the dominant nitrogen-suckers on the plant. If the plant is greening up, the bolls aren't pulling the nitrogen. Since we don't sell stalks, such a foliar feed would be pointless.”

How much fertilizer did fields lose to leaching from rainwater?

It's very hard to estimate although, especially in sandier soils, leaching occurred, says Espinoza. To prepare for next season and to track any potential problems, he recommends farmers have on hand several nutrient monitoring kits. The kits — a service offered by the University of Arkansas — cost $30 and allow a field to be analyzed through petiole analysis six times during the season. Turnaround for a test is rapid — data is often available within 24 hours.

The results “help farmers visualize how the plant is doing nutritionally,” he says. “A farmer, of course, can just pull one sample. That's better than nothing, but it's just a single snapshot. The best information comes from a season's worth of samples so we can see what the trends are.”

Roots, irrigation, PGRs

As soon as a cotton plant begins blooming, its root activity decreases gradually. The further a crop continues through a season, the less ability the roots have to “use” soil-applied fertilizer, says Robertson. “That's why, later on, we prefer to go with a foliar fertilizer.”

Another issue with abundant, recent rains is shallow root systems. “If you apply something like urea, there's a good chance that the roots won't have enough time to intercept that nutrient,” says Espinoza. “For example, assume the root system is 6 inches long. If the fertilizer moves below the root mass, it's no longer available. That's why, in years like this, it's best to go with foliar.”

Another thing that's true is a plant with a shallow root system and a good fruiting load is very susceptible to stress. Espinoza says such plants don't have a “buffering ability” since roots may be concentrated at the soil surface — which dries down fastest — instead of deeper down.

Farmers must pay attention to a crop's moisture situation, says Robertson. And, because of the shallow root systems, producers must be “doubly” careful because it can be just as bad to over-water as not water enough.

“From here on out, we've got to baby this crop,” says Robertson. “I think we may need to irrigate more frequently, with less water. If you've got a flat field that takes a while to irrigate, I'd consider watering every other row and pushing the water through — maybe flushing it like is done in rice. You know, if we don't water properly, any foliar feeds being applied now are a wasted expense.”

Espinoza says he's been in a lot of cotton that didn't receive much fertilizer and still remains green. That, he says, means the soil has a good amount of residual nitrogen.

“We've been encouraging farmers to take deep-soil samples to see how much nitrogen is available. It makes me wonder if there's more nitrogen than is suspected, and that's why we use so much PGR (plant growth regulator) here. Some Arkansas farmers use 60 ounces of PGR to control the crop. That may be unnecessary since we could have a reservoir of nitrogen in the soils that's available to crops planted early. Perhaps we can manipulate the crop to take advantage of it. We need to study that possibility.”

Counting on top crop

Robertson has spoken to a few producers who believe they have a cotton crop as good as last year's.

“However, I believe that's the exception to the rule. I visited a farmer a couple of days ago, and he said his good fields are as good as they've been in the last couple of years. His low spots, though, are much worse, and he thinks the overall yield will be brought down.”

Across the state, farmers are counting “very heavily” on the top crop. Some of them had rain for almost a month with heavy cloud cover.

“The top crop is at a critical stage right now,” says Robertson. “And we've got a bunch of fields right on the verge of cut-out. If you look at the calendar, the last squares we can count on harvesting will be ready Aug. 10 through Aug. 15. It's late in the game. We must do the best we can to get the fruit set and filled.”

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