Now that the December USDA crop report is past, the corn and soybean trade will focus more closely on crop growth in South America, weather forecasters say.

"Right now there are some trouble spots to note," Freese-Notis Weather reported on Monday in its daily Agriculture.com report.  "Argentina had very good planting weather for their corn and soybeans crops for October and November...but the final days of November were dry and December so far has been quite dry as well." Dry weather remains in the forecast for the next week, the weather service said.

Besides the scant rainfall, heat has become a factor in Argentina, too. "Yesterday, marked the fifth straight day with a high of 90 degrees or higher for some spots and we saw extremes to 96-98 degrees there for this past Friday and Saturday," Freese-Notis reported.

Brazil has weather issues developing as well. "Dryness remains a concern across southern Mato Grosso and northern Mato Grosso do Sul in northwestern Brazil and continues to increase across Rio Grande do Sul in far southern Brazil," said Kyle Tapley, MDA EarthSat Weather.

"Only limited relief is expected in these areas over the next 10 days, so corn and soybean growth will remain stressed," Tapley said.