Corn also edged down, capped like soybeans by expectations that drier weather would let harvesting in the Midwest pick up after a rain-hit start.
Wheat was similarly weak, with the cereal still facing pressure from large stocks and keen export competition from Russia.
The most active soybean futures on the Chicago Board Of Trade were down 0.1 percent at $9.83-3/4 a bushel by 1207 GMT.
"The market was concerned about the impact of adverse weather in the US and Brazil but those concerns have abated in recent days," said Phin Ziebell, agribusiness economist, National Australia Bank.
Soybean futures rallied to above the psychological $10 threshold at the end of last week after the US Department of Agriculture (USDA) surprised the market by trimming its monthly forecast of the US soybean yield.
"The soybean market confirmed its incapacity to stay above $10/bushel. The return of dry weather in the US will allow farmers to speed up harvest works," consultancy Agritel said in a note.
Oilseed markets also lacked impetus from Asia where Malaysian palm oil futures did not trade due to a public holiday.
Weather forecasts also eased worries about the South American planting season.
Weather models also forecast rains across Brazil in the week ahead while parts of Argentina have turned drier after excess rain in recent months.
Brazilian soy producers had planted 12 percent of their 2017/2018 crop through last Thursday, in line with a five-year average but behind the pace of the prior cycle, amid a lack of rain in key producing regions, consultancy AgRural said on Monday.
The most active CBOT corn futures were down 0.1 percent to $3.49-1/2 a bushel, while CBOT wheat eased 0.6 percent to $4.32-1/4 a bushel.
Beneficial moisture for dry wheat belts in the United States, Australia and the Black Sea region have also reduced price support for the cereal and underlined a backdrop of record global inventories.