McCarty: `...we're looking at a variety by environment reaction' Mississippi's harvested cotton yields this year continued the downward slide of the past few years, dropping below 700 pounds per acre for the first time since 1995.
Since 1995, average cotton yields in the state have risen to a record high of 901 pounds per acre in 1997 and have declined each year thereafter. That is, from 622 pounds in 1995, to 819 pounds in 1996, to 901 pounds in 1997, to 737 pounds in 1998, to 704 pounds in 1999, and then to 649 pounds in 2000.
According to Will McCarty, Extension cotton specialist for Mississippi, there is some question, however, as to whether or not the disappointing cotton yields across the state this year are proof of an overall downtrend in cotton yields.
"The recent downtrend in yield is very significant in our lives. But in history, this may just be a blip on the screen. Either way there are some things we need to manage around so yields don't continue to decrease," McCarty told his audience at the Cotton Short Course, Dec. 6-7, at Mississippi State University.
"I think what we're looking at is a variety by environment interaction," he said. "We do know that it can get too hot for cotton if the greatest number of heat units hits during boll development. All we need are 2,700 or 2,800 heat units to produce a tremendous cotton crop."
While excessive heat during the growing season is a limiting factor in cotton yield potential, it's not the only factor, McCarty says. "It's true that the hotter it gets, the lower our yields are, but, the high temperatures are only a factor. Heat hasn't caused all of our yield problems in cotton."
Other factors in this apparent yield drop are soil type, variety selection, and the interaction between the two. "We're putting more and more cotton on marginal land under hotter and drier weather conditions," said McCarty. "The more number two and number three land we put cotton on, the lower our yields will be."
In addition, he says, a vast majority of the state's cotton acreage is planted in transgenic varieties with a Coker background. In 2000, Mississippi growers planted 87 percent of their acreage in transgenics.
This limited variety base and its interaction with the environment may be partly to blame for the cotton quality problems experienced by many Mid-South growers in 2000. After harvesting what, in many cases, were disappointing yields, many cotton growers were dealt a second blow when they found themselves subjected to heavy discounts for high micronaire, short staple length, or both.
"Fiber quality is important to you. It's costing you money," said John Creech, Extension cotton specialist at the Delta Research and Extension Center in Stoneville, Miss. "The bottom line in variety selection is your bottom line. Balance the technology and other factors to see which variety and production system will make you the most money.
"Treat transgenic seed as another tool. Before you decide whether to plant transgenic seed, put it to the pencil test to see if it will provide you with an economic advantage or not," Creech said.
McCarty added, "If you need the technology transgenic varieties offer, then they're a good tool, but don't use that technology as your only basis for variety selection."
Both Creech and McCarty recommend growers place more weight on a variety's performance over multiple years and locations than on a single year's performance in state variety trials.
McCarty said, "On the bulk of your acreage, plant what you have the most experience with on your farm. Then, on smaller acreage, try new varieties that interest you and that have performed well in different environments."
"If you're planting something that hasn't been tested in multiple years, plant quality seed on a very limited amount of acreage," Creech said.
Even with what appears to be a downtrend in cotton yields, McCarty said, "Cotton is still the best game in town." He anticipates cotton acreage in Mississippi will increase to at least 1.3 million acres in 2001.