By STEVE ROTHWELLNEW YORK (AP) â¿¿ Wheat prices are rising to end the week with their biggest gain since last year's drought amid concern that dry weather will harm this year's crop. Futures prices for the grain have risen 5 percent this week, the biggest weekly advance since July. A lack of rain in the plains region may harm this year's crop in the U.S. and dry weather in Australia may also damage the crop there. Wheat for March delivery rose 10 cents to $7.9125 a bushel Friday. In other trading, corn also ended higher. The price of the grain has advanced nine days out the last 10. Soybeans ended the day slightly lower. Trading of metals was mixed. Gold, platinum and palladium fell, while silver and copper rose.