Crop prices soared on Tuesday, helped by a rash of buying across financial markets, sending Chicago soybeans back above $9 a bushel and London wheat on course for its first close for a month above £100 a tonne.

Growing expectations of a frost this weekend to end the growing season for much of the US corn crop were a major reason for the rise.

Temperatures west of the Mississippi River are on course to drop to -2 to -3 degrees centigrade (high 20s to mid-30s Fahrenheit), according to Meteorlogix.

While not unnaturally early, a frost has proved especially concerning this year because of the tardy state of US crops, with official data late on Monday showing 57% of corn mature compared with an average of 84% by now.

"This slow rate of maturity means these crops, especially corn, are vulnerable to damage should a freeze hit the northern half of the Midwest late this week, as currently forecast," Vic Lespinasse, the GrainAnalyst.com analyst, said.

Record for gold 

However, the rally was also helped a weakening dollar, making US-denominated assets, such as crops, more competitive on export markets.

The dollar's slide was blamed in part on a report that Gulf investors were considering abandoning the currency for oil trading.

It also reflected a growing appetite for risk. Investors have viewed the greenback as a safe haven during the economic crisis.

Equities soared, with major European indices closing more than 2% higher and US stocks showing 1%-plus gains at 19:15 GMT. Oil was 0.8% higher, at $71.00 a barrel, while gold topped $1,040 an ounce earlier to hit a record high.

"Crude oil has risen along with the stock markets helping to move all commodity markets higher," Hugh Schryver, at Glencore, said.

Crops leap 

In Chicago, traders noted widespread buying by speculators including major funds, with triggers for so-called buy stops - automated purchase trades – being hit to send prices higher still.

Corn for December jumped 8.3% to $3.70 a bushel at one point before retreating to close at $3.58 ¼ a bushel, up more than 4% on the day.

Soybeans ended 2.9% higher at $9.10 a bushel, having touched $9.21 a bushel earlier.

Wheat was also helped to a strong performance, ending up nearly 4% at $4.60 ¼ a bushel. That jump more than made up for weakness in the dollar to spur buying across the Atlantic too.

Paris milling wheat for November closed E1.75 higher at E125.25 a tonne. London feed wheat ended up £1.90 at £100.50 a tonne, having not closed above a ton a tonne since August 27.

November rapeseed finished E4.00 higher at E258.75 a tonne.