The U.S. cotton industry loses from $600 million to $750 million per year to contamination that creates production and quality issues for mills.
“That’s a significant loss,” says USDA ARS Engineer John Wanjura, at the USDA ARS Gin Lab in Lubbock, Texas.
Contamination, mostly plastic, results in a loss in premiums U.S. cotton merchants once enjoyed because of its reputation as a cleaner, higher-quality fiber compared to cotton from competing trade areas with similar quality, Wanjura says.
“Now, the premium has declined below that net zero line, compared to others.
“Growers also are beginning to see losses, up to 4,000-point discounts per bale. That’s a huge portion of the value of a bale,” he says. “Additionally, merchants and mills often won’t accept bales with plastic contamination calls.”
Reputation at stake
Those are direct losses, he says. Indirect losses may be even more damaging. “Lost reputation of U.S. cotton is probably the largest thing we risk from contamination,” Wanjura says. “We jeopardize market share and ability to maintain markets. If buyers don’t want U.S. cotton because of too much contamination, we lose our reputation for clean, high-quality cotton. Once we lose that favorable reputation, it’s almost impossible to build it back or it takes a long time.”
Plastic poses the biggest contamination threat, Wanjura says. “The issue has increased significantly over the last several years with adoption of harvesters that form modules onboard and wrap them in plastic. Information from AMS classing offices shows the primary source of contamination is module cover material.”
He says yellow and pink plastic wrap make up the highest percentage of contaminants. “Blue and orange plastic also show up in lint samples.”
Wanjura says module wrap is not the only contaminant. “There was a baseline level of plastic contamination before the round module harvesters. Shopping bags, black plastic used in vegetable production, and other plastic products have been problems and continue as a significant source of contamination. But wrap from round modules is now the predominant source.”
Preventing cotton contamination begins in the field, Wanjura says. Field sanitation is a starting point. He says scouting fields before harvest will eliminate a good percentage of the shopping bags and other potential contaminants.
“We see more of these contaminants around urban, higher population areas. Pay attention to field edges. Removing contaminants from those areas will go a long way toward removing field contaminants.”
He says picking up trash while performing other field operations —plowing, planting, baling hay, cutting stover, and other chores — will reduce contaminants. Removing plastic mulch instead of plowing it in also eliminates another contamination source.
“It’s better to do it ahead of time than risk forgetting and leaving it in the field.”
It’s worth the time to scout early and to pay attention from the harvester driver’s seat, Wanjura says.
“Stop the harvester, get off, and pick up shopping bags, pieces of twine, and other debris. Leaving them costs money. Plastic calls and the discounts add up.”
He says some ongoing research is looking at drones to identify plastic material in fields before harvest. Nothing is on the market now, but tools may become available in the future.
Harvester Setup and Operation
Manufacturer recommendations should be followed for proper harvester setup and maintenance to help prevent contamination from wrap damage by the machine. “Pay attention to settings on the round module builder belts, feed floor, and guide rods. Make sure the baler belts track properly and have the right clearance with the side walls of the machine to prevent wrap tears. Check that the steel guide fingers have proper clearance with the baler belts and are not touching them. Also, make sure the feed floor belts are set correctly to feed the wrap into the baler properly.
“When unloading a module from the machine, make sure to move the harvester away from the module before raising the handler and making a turn back into the field so that the handler doesn’t hit the module and damage the wrap.”
Module management during harvest is critical to reduce potential for plastic wrap contamination. Where modules are dropped, stored, and how they are arranged and moved may reduce opportunities for contamination.
Wanjura recommends dropping modules along field borders, if possible, to limit stalk damage.
During harvest, however, round bales are typically dropped in the field before being moved to a convenient storage area.
“If modules must be moved in the field, take care to avoid stalk damage and other obstacles that may damage the wrap,” Wanjura says. “When modules drop in the field, make sure the machine used to retrieve them lifts high enough that modules do not hit stalks that can perforate the bottom of the plastic wrap. A lot of the contamination we see at the gin comes from failed covers.”
He says wrap damage may be so bad that it gives way under the load of the cotton. “What’s left is a big pile of cotton with plastic in it. When the gins pick up the module, the wrap remains in the cotton.”
A safe storage area will protect the cotton until the gin picks it up.
“Staging at the edge of the field is best,” Wanjura says. “Place modules on an elevated surface so rain will run off and the modules do not sit in water. The staging area should be free of rocks and other material that will damage wrap.”
Wanjura says some fields with pivot irrigation will have corners where wheat or grass grows. Those make good staging areas. “Also, growers might disk up an area to remove stalks, leaving nothing to puncture the wraps.
“Leave adequate room around each module so transport
vehicles can access them quickly and easily.”
He recommends not sliding modules on the ground while staging, loading, or unloading. “Abrasion from sliding modules can be enough to cause the wrap to fail. Also, modules are picked up multiple times and each time adds potential to fail. If wrap is not damaged, this is a pretty robust system for protecting the cotton,” Wanjura says.
He recommends leaving space between modules to allow for air movement and to minimize tipping contact during loading on conventional module trucks. He says 6 to 8 inches, flat face to flat face, between modules leaves room for air flow and to prevent rain from collecting. “Also, place modules far enough apart to prevent them from tipping over into other modules as they are loaded. Tipping and contact causes the module to slide and damage the wrap.”
At the gin
Plastic wrap contamination also occurs at the gin. “Unwrapping at the gin is a big concern,” Wanjura says. “Often, a gin worker cuts the wrap with a knife as it comes off the truck. Where he cuts the plastic is important. The recommended cutting zone is around the outside of the module, 180 degrees from a large, white, human-readable tag on the outside of the module close to one of the flat ends.
“In an automated positioning system, the scanner should look for RFID tag position #8. The module has tag position numbers 2, 4, 6, and 8. The cut should be positioned on the opposite side of the module from RFID tag position #8.”
Ideally, Wanjura says, workers should cut the wrap only once to reduce the risk of contamination. “If it’s cut at two locations, the risk of cutting at the wrong spot increases.”
Research is ongoing on ways to remove plastic contaminants from cotton in the gin. Those efforts should help reduce the number of plastic calls and help maintain the reputation of U.S. cotton, Wanjura says.
But the crucial factor in limiting cotton contamination is prevention, a chore that begins before harvest and continues to the gin.