* Dollar index recovers from five-week low * U.S. stock indexes surrender gains; agricultural shares down * Aussie dollar skids after RBA chief hints at rate cut * Chinese central bank injects cash for first time since February NEW YORK, July 30 (Reuters) - Stocks gained slightly in volatile trade on Tuesday as investors positioned ahead of this week's meetings of the U.S., British and euro zone central banks, while the dollar climbed from its recent five-week low. A pick-up in euro zone consumer and business confidence gave stock markets an initial boost ahead of policy clues from the Federal Reserve, European Central Bank and Bank of England, and Friday's U.S. jobs report for July. As the New York session wore on, stocks struggled to maintain gains and indexes turned flat or negative. Verizon and Mosaic led a selloff in the telecoms and materials sectors. But heading into the close of the global trading day, investors again bought U.S. stocks, pushing two of the three benchmark indexes higher. "We're up against 1,700 on the S&P so it would take a lot to make it move substantially higher," said Jack de Gan, chief investment officer at Harbor Advisory Corp in Portsmouth, New Hampshire. "The nearest things on the horizon are the Fed meeting and the jobs number, so I think we're going to tread water here until that." The Dow Jones industrial average unofficially ended down 1.38 points, or 0.01 percent, at 15,520.59. The Standard & Poor's 500 Index was up 0.63 point, or 0.04 percent, at 1,685.96. The Nasdaq Composite Index was up 17.33 points, or 0.48 percent, at 3,616.47. MSCI's world index rose 0.1 percent, though it remained off the global day's session high, while the FTSEurofirst 300 index of top European shares closed little changed. Shares of potash producers and related agriculture companies were volatile after Russia's Uralkali dismantled one of the world's largest potash partnerships by pulling out of a venture with Belarus Potash Co. Uralkali said the decision might lead to a fall in the global potash price to below $300 per ton in the second half of 2013, from $400 per ton now. In New York trade, Mosaic Co fell 17.4 percent, Potash Corp slid 16.2 percent and Agrium Inc fell 5 percent. DOLLAR GAINS The U.S. dollar continued to edge away from Monday's five-week low as investors viewed its sharp drop over the last two weeks as a chance to get back in ahead of the conclusion of the Fed meeting and this week's growth and jobs data. The dollar index was last up 0.2 percent. "I think the Fed is not going to want to rock the boat, but what could change market expectations is the U.S. data that is coming out," said Alvin Tan, FX strategist at Societe Generale. "It is not only the Fed that is coming up tomorrow, we also have U.S. second-quarter GDP, ISM data and on Friday we have nonfarm payrolls ... if these come in strong, the market is going to start pricing in a faster tapering cycle again." Currency traders were also watching the Australian dollar , which reached a two-week low after hints from the central bank's governor of another rate cut at next week's Reserve Bank of Australia meeting. "(RBA) Governor Stevens' comments that the inflation environment remains soft came in on the dovish side at a critical juncture for sentiment," said Christopher Vecchio, Currency Analyst at DailyFX in New York. In Asia, Japan's Nikkei bounced up 1.5 percent as the yen eased, though stocks elsewhere in the region finished flat. China's central bank's first injection of funds into money markets since February was balanced by some mixed data. COMMODITIES PRESSURED Commodities stayed under pressure on concerns about China's outlook. Analysts polled by Reuters forecast data on Thursday will show its manufacturing sector may have shrunk in July for the first time in 10 months. Copper hit a three-week low, gold fell 0.1 percent and U.S. crude lost 1.4 percent to change hands at $103.11 a barrel. German bund futures were little changed at 142.41 before this week's ECB meeting, where the central bank is expected to give some details on its plans to provide "forward guidance" on rates for the first time. U.S. Treasuries prices were choppy as traders positioned for the release of second-quarter U.S. economic growth data, the Fed statement and the Treasury's next refunding announcement, all due on Wednesday. Benchmark 10-year Treasury notes slipped 1/32 in price, the yield at 2.6007 percent from 2.61 percent late on Monday.