Dryness in Iowa means the top US soybean producing state could see only a small improvement in yields from last year's drought-hit result, farm officials warned, cautioning over setbacks from inundations in the South East too.
Below-average rainfall rates for July - which for much of the Midwest was the driest since 1985, excluding 2012 – "may curtail yields" in parts of the western Corn Belt, US Department of Agriculture officials said.
"Without some improvement in moisture conditions, Iowa soybeans may yield only modestly better than they did during last year's drought," they warned.
Last year, Iowa's soybean yield tumbled 13.6% to 44.5 bushels per acre, a decline more than twice the national average.
Indeed, the Iowa yield was only 12.4% above the US average, well below an average of 20% for the previous five years.
The dryness means that August weather "will again be a critical factor for Midwestern soybean yields", the USDA said, noting that so far "stress on crops has been tempered by seasonally mild temperatures".
The delayed maturity of plants too is significant, meaning that soybeans "may require regular rains and warm-frost-free days well into September this year to sustain normal crop development".
The comments come amid concern at a dry and warmer trend in the Midwest weather outlook, with WxRisk.com noting that the six-to-10 day forecast from the European weather model "is much warmer over the upper Plains and Midwest than normal".
"Some" rain was due in parts of North Dakota, South Dakota, Minnesota and Wisconsin, but not until around August 23, the weather service added.
'Scouts would be shocked'
Meanwhile, some commentators have cautioned over upbeat findings for Iowa from crop tours, of which the next one, the ProFarmer event, is due next week.
"I am sure they will find 250-300 bushels-per-acre corn," Mike Mawdsley, an Iowa-based farmer and broker, said
"But I am also sure some that have not been out this way will be shocked by the size of the soybeans, the stage of maturity of the corn, and the bare ground," where spring rains prevented plantings.
'Seal the fate'
And noted crop scout Michael Cordonnier warned earlier this week, after an Iowa crop visit, that "the worst thing for the soybeans would be if the temperatures warmed up to above normal and it stayed dry.
"That would seal the fate of many of the soybeans."
"There is a lot of moisture stress appearing on the soybeans, but the cooler temperatures have kept the stress from being even worse.
"The soybean crop in Iowa is going to be below trend line, it's just a matter of how much below trend line."
'Serious damage to crops'
The USDA officials also cautioned that soybean yields in the US South East looked set to fall short of last year's bumper levels, which saw Alabama, for instance, beating Iowa with a 45.0 bushels-per-acre result, up 36% year on year.
"The South East's record-high soybean yields last year are unlikely to be duplicated due to harm from excessive moisture."
And rainfall levels in the region look set to remain high, with WxRisk.com saying that for the next five days the European weather model shows that "all the [US] rain remains over the central Gulf coast and over the south eastern states".
"The strong tropical feature in the western Gulf of Mexico will likely become a tropical storm and hit the eastern Gulf of Mexico on early next week," the weather service said.
"Given how wet the south eastern states have been all summer, a tropical storm… will only add to the rainfall amounts in this area and could cause widespread flooding for Alabama, Georgia, South Carolina and North Carolina, and could do serious damage to crops."
Besides soybeans, the South East rains are also of particular concern to cotton prospects, and have helped lift New York's December cotton contract above 90 cents a pound this week for the first time since March last year.