* Fiber jumps as U.S. postpones tapering
* Commodities markets, financial markets see broad-based gains
* China makes first 2013 cotton purchase -industry association
NEW YORK, Sept 18 (Reuters) - Cotton futures rose the most in a month on Wednesday, as the U.S. Federal Reserve's decision to delay trimming its bond-buying program prompted broad-based buying of commodities.
The most-active December cotton contract on ICE Futures U.S. finished up 1.1 cents, or 1.3 percent, to settle at 85.54 cents a lb.
It was the second month's biggest one-day gain since mid-August when it hit a five-month peak of 93.72 cents a lb.
Gains gathered pace after the U.S. central bank decided to postpone tapering its massive stimulus program bond-buying and ending the era of "easy money" that has fueled investment in financial and commodities markets.
Further, the big fiscal stimulus program has sparked expectations of increased inflation down the line, encouraging buying of commodities.
Seventeen of the 19 commodities in the Thomson Reuters-Jefferies CRB index were up, and U.S. stocks soared on the news.
"The markets factored in a big cutback, and got nothing. All of these markets have gotten a big push by the Fed. We thought it would end, but it looks like it's not," said Michael Smith of T&K Futures & Options, a Port Saint Lucie, Florida-based brokerage.
Beijing bought its first round of cotton from the 2013 harvest, according to an industry association said.
The start of China's stockpiling program for the 2013 cotton crop underpinned the market, though the first reserve purchase did not jostle the market as it was widely expected.
China has said previously it would continue building its strategic reserves this year, though broad changes to the controversial program are expected next season.
The government program has driven voracious demand for lower-priced, foreign cotton since it was launched in 2011.
Uncertainty remains over Beijing's plans for cotton auctions later this year.
December cotton climbed to an intraday high near its 100-day moving average of 85.56 cents a lb.
Prices have been supported above 83 cents by small-scale buying in the physical market, but a lack of interest from both mills and speculators have kept the market capped, dealers said.
Noncommercial dealers have dropped their bullish bet in cotton futures and options to the lowest level since January, Friday's U.S. government data showed. (Reporting by Chris Prentice; Editing by Diane Craft)