* 6th straight session gain marks longest run in more than 1 month
* Decrease in 2013/14 U.S. plantings seen supporting prices
* Technical support level at 85 cents a lb - dealers
NEW YORK, March 5 (Reuters) - Cotton rose for a sixth straight session on Tuesday, after reaching a 10-month high, as mill buying continued even in the face of a recent bull run driven by speculative investment.
The most-active May cotton contract on ICE Futures U.S. gained 0.72 cent, or 0.8 percent, to settle at 86.98 cents per pound, after reaching 87.45 cents, the highest price since May 8, 2012.
Tuesday's close marked cotton's most extended series of daily gains since the end of January. Demand from global consumers, particularly in top buyer China, has not been deterred as prices have climbed to a 10-month high and have surged nearly 14 percent since the start of the year.
"There was some buying interest from China, and some buy stops are getting triggered," said Joseph Ricupero, vice president at RJ O'Brien in New York.
Growing concerns over the size of next year's crop in the United States, the world's top exporter, have underpinned the recent rally.
Macquarie analysts pegged the U.S. 2013/14 cotton crop at 9.4 million acres in a research note on planting expectations on Monday, down by 2.4 million acres from the current marketing year. The USDA and National Cotton Council have also forecasted a smaller crop next year.
"We're planting fewer acres in the U.S. You have to have that in the back of your mind, especially if you're a mill. And our certified stocks, as quick as they went into the warehouse, they could leave," said Nick Gentile, senior partner of commodity trading consultancy Atlantic Capital Advisors, referring to a recent surge in exchange stocks.
Certified stocks have climbed to the highest levels in more than 2-1/2 years, totaling nearly 432,000 480-lb bales on Monday, according to ICE data. Another almost 8,000 bales awaited approval by the U.S. Department of Agriculture on Tuesday.
Those levels have risen steeply from about 94,000 bales at the start of the year and fewer than 8,000 bales in mid-October.
Much of cotton's technical backdrop is bullish, with the most-active contract having surged through a resistance level of around 85 cents that now serves as price support, brokers said. They cited the next resistance level in the range of 89.50 cents to 90 cents, based on levels seen in early May 2012.
Fiber's recent bull run has been fueled by speculative investment, with noncommercial dealers holding a large net long position in cotton futures and options.
The most-active May contract has been in technically overbought territory, with a 14-day relative strength index above 80, since the end of January. (Reporting by Chris Prentice; Editing by James Dalgleish)
