Soy futures jump as US crop deteriorates in hot, dry weather

* USDA rates soy, corn crops worst since 2012

* Traders expect USDA may cut soy yield estimate

* Next USDA supply/demand forecasts due Sept. 12

CHICAGO, Sept 6 (Reuters) - Chicago Board of Trade soybean futures jumped on Wednesday after a weekly U.S. government report showed crop conditions deteriorated more than expected during a hot, dry spell.

The reduced crop rating fueled expectations among traders that the U.S. Department of Agriculture may cut its yield forecast in a monthly report due out next week.

The USDA is already projecting domestic soy ending stocks will fall to an eight-year low in the 2023/24 marketing year, leaving little supply cushion.

The government, after grain markets closed on Tuesday, rated 53% of the soybean crop as good to excellent, down 5 percentage points from a week earlier and below the 55% expected by analysts. The corn crop's rating also fell below analysts' expectations.

Good-to-excellent ratings for both crops are the lowest for this time of year since 2012, a historic drought year, and renewed concerns about crop stress.

"There are key states that are now not looking great," said Ted Seifried, chief market strategist for Zaner Ag Hedge.

In Iowa, the second biggest U.S. soybean-producing state, 49% of the soy crop is in good to excellent condition, down 17 percentage points from a year ago, according to USDA data. Wisconsin's good-excellent rating is down 23 percentage points from last year at 55%.

The USDA's latest soy yield forecast, issued in August, was for 50.9 bushels per acre, up from 49.5 bushels last year. Traders said the government may need to lower its estimate in a Sept. 12 report.

A farmer survey published Wednesday by brokerage Allendale forecast yields at 49.58 bushels.

"There is more and more talk of a soybean yield that is under 50 bushels per acre," said Tomm Pfitzenmaier, analyst for Summit Commodity Brokerage.

Most-active soybean futures were up 10-1/4 cents $13.75-1/4 a bushel by 11:45 a.m. CDT (1645 GMT). Corn was flat at $4.86 a bushel and wheat was up 11-1/2 cents at $6.10-3/4 a bushel.

(Reporting by Tom Polansek in Chicago. Additional reporting by Gus Trompiz in Paris and Naveen Thukral in Singapore; Editing by Subhranshu Sahu, Alison Williams and Sharon Singleton)