NEW YORK (AP) — Standard & Poor's Ratings Service lowered its outlook on Archer Daniels Midland Co. to negative Friday, saying that severe droughts in the U.S. could hurt the agribusiness conglomerate's income and credit ratings over the next year to 18 months.

Standard & Poor's said the company's net income may weaken in the second half of 2012 because of smaller soybean and corn harvests, and it said Archer Daniels Midland may continue to buy back stock in spite of the risk of lower profits and higher grain prices. It still has an investment-grade 'A' rating on Archer Daniels Midland's credit, which covers about $10.3 billion in company debt.

The firm previously had a stable outlook on the Decatur, Ill., company's credit. Its current 'A' rating is five notches above "junk" status.

Much of the U.S farm belt is suffering through the worst drought in a quarter-century. According to the U.S. Department of Agriculture, about half of the nation's corn crop was rated poor to very poor this week, and 37 percent of the soybean crop was in the same category.

Shares of Archer Daniels Midland rose 35 cents to $25.48 in midday trading.