July 31 (Reuters) - Commodity funds bought a net 4,000 Chicago Board of Trade wheat contracts on Wednesday, trade sources said. They bought 2,000 corn and were net even in soybeans. Corn Soybeans Wheat Soymeal Soyoil July 31 + 2,000 even + 4,000 +1,000 -1.000 July 30 + 5,000 - 7,000 + 2,000 -3,000 -1,000