Chicago wheat edged lower on Thursday, heading for a fourth session of declines on improving condition of the U.S. winter crop, while corn gained more ground to reach a one-week top.

Soybeans were slightly lower.

The most-active wheat contract on the Chicago Board of Trade dropped 0.2 percent to $4.62 a bushel by 1111 GMT, after closing down 2.3 percent on Wednesday when prices hit a one-week low near $4.61 a bushel.

Soybeans fell 0.2 percent to $9.06 a bushel and corn added 0.2 percent to $3.58-3/4 a bushel, after hitting $3.61 earlier, the highest since March 31.

"Wheat crop condition is improving in the U.S. Plains, which dragged down prices, but there is some buy-side interest in U.S. wheat at these prices," said Kaname Gokon at brokerage Okato Shoji in Tokyo.

The U.S. Department of Agriculture on Tuesday rated 59 percent of U.S. winter wheat as being in good-to-excellent condition. That was above analysts' estimates for 57.6 percent of plants for summer 2016 harvesting, and the five-year average of 42 percent.

Corn has been buoyed by expectations U.S. farmers could plant less corn than forecast, turning instead to soybeans, because of rainy weather during sowing period, and expectations of a slowdown in Brazilian corn exports after a speedy pace of exports at the start of this season.

Possibly bearish for soybeans, China is aiming to reduce corn planting by about 8.2 million acres by 2020 and boost soybean output, in order to meet domestic food demand, the ministry of agriculture said on Thursday.

It will encourage farmers in arid areas to shift to silage corn and alfalfa, while northeastern corn producing provinces would resume the rotation of corn with soybeans. Informa Economics on Wednesday raised its estimates of 2015/16 corn and soybean production in Argentina, while lowering its estimate of Brazil's soybean crop, trade sources said.

The firm, in a monthly report, projected Argentina's 2015/16 corn harvest at 27.5 million tonnes, up from 27.0 million. Informa estimated Argentina's soybean crop at 59.5 million tonnes, up from 59.0 million last month.

However, soybean harvesting in the country's main production regions was halted by rain last weekend, and rain this week is expected to cause further delays.

Commodity funds sold an estimated net 6,000 CBOT wheat contracts on Wednesday, trade sources said. The funds were net buyers of 5,000 soybean contracts and 4,500 corn contracts, traders said.