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In Louisiana Sugarcane: shifting varieties and fertilization

The annual LSU AgCenter-sponsored sugarcane survey does more than keep track of acreage. It also points researchers to areas of needed study.

Partially as a result of the survey, fertility in sugarcane has recently been under more scrutiny. LSU has updated fertilizer recommendations and researchers have been touting those during winter producer meetings.

The survey is compiled with the help of Extension agents in each sugarcane-growing parish (currently numbering 23 after East Baton Rouge Parish stopped growing sugarcane). The agents send a questionnaire to all growers.

“The data I get back are each operation's amount of cane acreage — first, second, third, fourth stubble, whatever the case — and all the varieties they plant on the farm,” says Ben Legendre, LSU AgCenter sugarcane specialist.

“I gather all that in the form of a variety census covering the three regions of the state — the Mississippi River/Bayou Lafourche region, the southwest region along Bayou Tech, and the northern region including the parishes of West Baton Rouge, Point Coupee, St. Landry, Avoyelles and Rapides.”

The survey gives the sugar industry an idea of the varieties being grown and other trends occurring across the state. “It helps us know how new varieties are being adopted and lets us know when older varieties are tailing off.”

Researchers also use the survey to plan projects. “If you have a variety that's susceptible to a particular disease, a pathologist may want to work with it, especially if the variety is increasing in popularity.

“That was the case with LCP 85-384. When rust arrived, 384 was still very productive. We were able to use the information in the variety survey with EPA to show a majority of our acres were planted in this one variety.”

Currently passing on 384, cane growers are using newer varieties like HOCP96540 and L97128.

Legendre says the survey is partly responsible for current studies in sugarcane fertility. “Some new issues have come up. When we were using anhydrous ammonia, we basically had to apply 20 to 30 percent more nitrogen than was needed, because we lost so much nitrogen.

“With the new material — 32 percent UAN — we can apply only what the plant needs. So the varieties may respond a bit better, but we also have a better fertilizer product to use.”

Since he's been at LSU, “we've looked at fertility requirements — especially N — for our varieties. What we found is that prior to 2000, the recommendations were based on anhydrous ammonia.”

As a result, the major variety for years, 384, tended to lodge very badly. Research between 2000 and 2002 found “when we used high levels of fertilizer — especially N — using UAN-32, we were losing yield. The cane would lodge, we couldn't pick it up with the combine, and we were losing sugar because the excess N caused maturity to be delayed.”

During those three years of study, researchers worked with many parish agents around the state on both light- and heavy-textured soils. They found the same thing wherever they went.

“The 140- to 160-pound N recommended on heavy soils, particularly, and the 120- to 140-pound N on light-textured soils, were way too much.”

Since then, acreage has shifted away from 384 to the newer varieties. But research (Rich Johnson with USDA has done subsequent studies) has found the same thing. With UAN-32, “we can go with less than 100 pounds in plant cane. Typically, though, research showed about 80 pounds of N was required. Eighty pounds. That's it!”

To reflect the new information, LSU AgCenter fertility recommendations have been altered. Most varieties — “this wasn't just a quirk of 384” — can provide maximum genetic potential at fertilizer rates about 20 to 30 percent less than recommendations prior to 2000.

There have been many questions about this from growers. “Over half our winter meetings have already occurred and fertility has been a major emphasis.”

For the upcoming crop, growers are facing costs of some 60 cents for a pound of nitrogen. Consider applying 140 pounds versus 100 pounds of fertilizer.

“That's $24 per acre savings there alone. A grower with 1,000 acres could keep $24,000 in his pocket. And the great thing is even with the lower rate, he'll have comparable, if not better, yields.”

It's not always an easy sell, says Legendre. The old-time farmers have been used to making yields based on high fertilizer inputs.

“We're now trying to convince them they don't need 160 units of N. Hopefully that message is getting through.

“But the truth is, a majority of the questions on this are coming from the long-time growers. Probably up to 20 percent of our growers still are using the highest fertilizer rates. They believe that's an insurance policy, that if there's rain they won't lose all the N and there will be a reserve available later in the growing season.”

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