PARIS/CANBERRA: Chicago corn and soybean futures fell for a fourth straight session on Tuesday to multi-week lows as the prospect of bumper US harvests and timely rain for planting in Brazil kept the focus on ample global supply.

Wheat futures also slipped as forecast for rain in parched Russian wheat belts eased supply concerns and took attention away from uncertainty over Russian export policy.

A slide in crude oil, as global demand worries persisted, also hung over grain markets.

The most-active corn contract on the Chicago Board of Trade (CBOT) was down 0.4% at $4.06-3/4 a bushel at 1153 GMT, with CBOT soybeans falling 0.7% to $9.89-1/2 a bushel and wheat slipping 0.2% to $5.84 a bushel.

Soybeans earlier touched their lowest since late August, while corn struck a three-week low and wheat a two-week low. Forecast rain in Brazil is set to break a dry period that hampered planting, with only 8.2% of the total expected soybean area sown by last Thursday compared to 17% at the same time last season, consultancy AgRural said.