Art Samberg is quoted in a debate by Barron's Roundtable:

“I'm recommending cotton -- the December ’07 contract. This is the other side of the growth story in agriculture. You're a farmer and you want to plant cotton? You've got to be crazy. You want to plant corn or wheat. Cotton consumption in the U.S. has fallen from 12 million to 5 million bales a year because of the growth of polyester and other stuff. But the real story is China, as it is with most things. In China, there is a booming fixed-asset investment across the textile industry. Spending in China was up 27% in ’06, after rising 36% in ’05. Chinese consumption of cotton had been growing by 4-6% a year. Now it's growing by 15% a year. China's consumption of cotton has gone from 25% to 39-40% of world cotton consumption. They are a large importer.

“The decline in U.S. cotton consumption had masked some of these trends. U.S. farmers are going to withdraw acreage. There have been only four times since 1913 when cotton was this cheap relative to grains like corn and wheat. The last time was in 1974, and farmers planted 16% less cotton acreage the next year. From the end of ’74 to mid-’76, the cotton price tripled.”
Continue.

A farmer will make more money in corn or wheat and even soybeans so why not switch to grains from cotton.
Next year the prices will be higher due to China's demand and due to less cotton being grown.