The price of corn jumped 1.7 percent to $8.3875 a bushel, while soybeans finished at $17.3025 a bushel, up 2.8 percent from Tuesday.

That left the corn price up 68 percent from June and soybeans 39 percent higher.

An all-time record hot July accompanied by nearly three months of extreme drought have baked the country's prime farmland in the midwestern and central states, where the world's largest corn and soybean crops are grown.

Prices jumped after reports from the annual Pro Farmer Midwest Tour gave analysts and traders more bad news on the state of the crops.

"Crops in western Ohio and eastern Indiana were far below the norm," said Pro Farmer analyst Brian Grete.

Yields in South Dakota meanwhile were called "stunningly low."

"The Pro Farmer tour sparked the rally" Tuesday, said Frank Cholly of RJO Futures.

"They have a pretty good peg at final yields," he said.

The Pro Farmer estimates were significantly lower than the US Department of Agriculture's sharply slashed forecasts from last week.

"We are getting less production from South America, so that forces buyers to go to the US," driving up prices, Cholly added.

On August 10, the USDA sharply reduced its production forecast for the globally crucial crops, saying output would likely be at the lowest level in six years.

Last week, they estimated that 50 percent of the corn crop was in poor or very poor condition, compared to 15 percent at the same time last year.

For soybeans, 39 percent of the crop was in poor condition or worse, compared to 13 percent a year ago.

The drought has also hit feeds for livestock like hay, forcing ranchers to trim their herds, which analysts expect could push up the price of meat in the coming year.

While drought and hot, dry weather has devastated agriculture this summer and led to the deaths of dozens of people, it has also decreased the outbreaks of tornadoes, scientists at the National Severe Storms Laboratory of the National Atmospheric and Oceanic Administration said.

Around 300 tornadoes have hit the U.S. since the middle of April, the fewest in that time period in nearly 60 years of record-keeping, they said.

That's about a third of the average major tornado incidents for the period.

"This is a really rare event," Harold Brooks, a research meteorologist at the storm laboratory, told The Wall Street Journal.

"The simple reason is: You aren't going to get a tornado if you don't have thunderstorms."

A high-pressure system has been parked over the middle of the United States, bringing oppressive heat but keeping severe storms with their precipitation -- conditions which can spawn tornadoes -- at bay.

July, the warmest month on record for the United States, saw the fewest tornadoes ever recorded for the month.

The simple fact, Dan Kottlowski, a senior meteorologist with Accuweather.com, told the Journal, is that rainfall brings tornadoes while drought keeps them away.

"Which side of the coin do you want?" he said.

Mayans made drought worse with crops
New York (UPI) Aug 21, 2012 - Mayans may have hastened the demise of their civilization by clearing forests, making an already naturally drying climate drier, U.S. scientists say.

Prolonged drought is thought to have contributed to the eventual collapse of Mayan civilization in Mexico and Central America, and forest razing for cities and agriculture may have made matters worse, the researchers said.

"We're not saying deforestation explains the entire drought, but it does explain a substantial portion of the overall drying that is thought to have occurred," lead study author Benjamin Cook, a climate modeler at Columbia University, said.

More than 19 million people were scattered across the Mayan empire at its height, between A.D. 250 and 900.

Using population records and other data, the researchers reconstructed the progressive loss of rainforest across their territory as the civilization grew.

Computer simulations of how lands newly dominated by crops would have affected climate suggest that in the heavily logged Yucatan Peninsula, rainfall would have declined by as much as 15 percent, while in other Mayan lands such as southern Mexico, it would have fallen by 5 percent.

As agricultural crops replace a forest's dark canopy, more sunlight bounces back into space, Cook said.

With the ground absorbing less energy from the sun, less water evaporates from the surface, releasing less moisture into the air to form rain-making clouds.

"You basically slow things down -- the ability to form clouds and precipitation," he said.

Overall, the researchers attributed 60 percent of the drying estimated at the time of the Mayans' peak to deforestation, a Columbia release said Tuesday.