KAMPALA (Reuters) - Uganda's coffee exports rose 28 percent year-on-year in July, while earnings rose slightly, industry regulator Uganda Coffee Development Authority (UCDA) said on Tuesday. UCDA said in its monthly report the east African country shipped a total of 403,381 60-kg bags last month, up from 314,304 bags in the same period last year. Earnings from the bean shipments rose to $40 million from $37.9 million in July 2014, it said. UCDA did not say in its monthly report what spurred the increase in export volumes. David Muwonge, head of marketing and production at the National Union of Coffee Agribusinesses and Farm Enterprises, said farmers probably released more stocks to get fees for the upcoming school term. "It's a cyclical thing, farmers will need a lot more money to pay fees so they were motivated to sell more," he said. Uganda's last school term for this year begins in September. Uganda is Africa's largest exporter of coffee, which is also one of the country's top foreign exchange earners. The regulator forecast exports in August would climb to 320,000 bags from 268,033 bags shipped in the same month last year but did not give a reason for the projected increase. Harvesting of the main crop is set to begin in the centre and east of Uganda.