Cotton bale moisture an issue

The ability to accurately measure moisture in a bale of cotton will add to the value of U.S. grown cotton in the export market and provide more reliable payments to producers.

Cotton has been marketed by weight in the U.S. for nearly 200 years and until recently little concern was given to moisture. Excessive moisture can add to weight and value of cotton, but excessive moisture will lead to loss of quality in storage.

With such a high percentage of U.S. cotton (roughly 70 percent in 2006) going for exports, it is especially critical to keep moisture levels low.

Finding a portable, easy to use and highly accurate meter to measure cotton moisture has become a high priority for USDA-ARS test facilities in Mississippi, Texas and New Mexico.

Speaking at the recent Southeastern Cotton Ginners meeting, Rick Byler, research leader at the Stoneville, Miss., ARS research facility, said researchers have identified several hand-held devices that may be able to do the job. Accuracy of these meters, durability, cost, and the speed and ease of use were focus points for the research, according to Byler.

“When I first started working with cotton, I was amazed there was no reliable way to measure moisture. I grew up on a dairy farm and measuring moisture in corn, soybeans and wheat was a routine part of our operation,” Byler said.

In 2005, the cotton industry determined excessive moisture in cotton to be 7.5 percent. Using 7.5 percent moisture content as a target, the USDA research team set out to find a reliable way to determine which bales of cotton did and did not measure up to this standard.

“I had a farmer call me last fall. He said he had sent his cotton to a warehouse and the warehouse had hired a consultant to check moisture. The consultant determined this farmer's cotton to be at 10 percent moisture. Based on a hand-held moisture meter reading, the warehouse intended to dock the price of this farmer's cotton, and the farmer was justifiably upset,” Byler said.

The big problem is that none of the hand-held devices used to measure moisture in cotton are certified. By comparison, in the corn industry there are certified meters. In cotton, there is no such program and no certified meters, Byler explained.

In the ARS study seven commercially available portable moisture measurement devices, consisting of a bale probe and display, were purchased and used. We used four different Stramberg meters, two Aquaboy meters and one Delmhorst meter.

We wanted to work with cotton from commercial gins, so we collected bales from the Southeast, Southwest and California-Arizona, Byler explained.

A total of 40 bales were prepared in several gins with regimes designed to achieve different moisture content. Each bale was measured in six locations with the seven measurement devices, lint samples obtained from the same locations, and the moisture content determined by the oven drying method.

We wanted to use bales with different moisture treatments, including ginning with little or no drying and no moisture restoration, medium dry with no restoration, normal drying with steam-type moisture restoration, normal drying with both steam and water-spreading restoration, Byler said.

Lint samples were gathered from the different locations and placed in an oven to determine moisture content. The meter readings were compared with the oven-based moisture content. The readings from all meters were improved significantly with linear corrections. It is unknown if the corrections found would be applicable to any particular meters other than those used in the study and these corrections may not be applicable with these meters at a later time because of drift, according to Byler.

Unfortunately, measured moisture content was consistently different from the oven-based samples versus data for each of the meters. A constant offset was then calculated for each device and later a linear fit with two coefficients was applied and several of the meters were comparable in accuracy.

The Delmhorst meter is the least expensive among those tested, costing $416. The Aquaboy that uses a screw-in probe was the most expensive ($1,900) and most difficult to find, Byler says. Some meters don't read below seven percent, which is usually not a problem because we were trying to determine 7.5 percent moisture.

“We have over 5,000 measurements in the data set, so it will take a while to get the whole picture,” Byler noted. Data from Stoneville showed variability using the Aquaboy probe from 6 percent to 12 percent on samples that measured 6 percent moisture in the oven tests. The Delmhorst meter gave a reading of 3 percent to a little over 6 percent, which looked best in the Stoneville test.

“None of the meters were impressively accurate. Each tracked moisture in that when the meter read higher the cotton was wetter and vice-versa, but the best meter was within 1.5 percent accurate. So, if you want cotton to be no more than 7.5 percent moisture, you would have to read 6 percent moisture to be sure cotton meets the 7.5 percent standard,” Byler said.

Byler said complete results of the bale moisture tests should be available in the summer of 2007.

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