The prime minister of Belgium set a goal yesterday of increasing the number of organic farms in his country by 60 percent a year for the next four years, with the aim of having at least 4 percent of the country’s agricultural land farmed organically. The target is part of a comprehensive sustainable development plan unveiled yesterday by the government that also would cut energy consumption in the country by 10 percent below 1990 levels by 2010 and greenhouse gas emissions by 7.5 percent. Renewable energy would provide 2 percent of the country’s power by 2010 and nuclear power would gradually be phased out. State Energy Secretary Olivier Deleuze said the plan was based on goals set at the 1992 U.N. Earth Summit in Rio de Janiero. “Belgium is the first country to have put forward such a global strategy to match the agreements first struck at the Rio conference,” he said.