Soybeans gave up some of their initial gains, however, as the market set relief at the 90-day negotiating period agreed by the world's two largest economies against the task ahead in resolving their dispute.
In a meeting on Saturday at a gathering of G20 countries in Argentina, US President Donald Trump agreed to hold off on new tariffs during the truce period while Chinese counterpart Xi Jinping pledged to purchase more agricultural products from US farmers immediately, the White House said in a statement.
"The initial agreement did include a specific promise for China to buy significant amounts of US agricultural products which, if realised, will be very supportive for prices," said Ole Houe, director of advisory services at brokerage IKON Commodities in Sydney.
"However, there is a long way to go to for both US and China before any real progress is made on the agreement and I think that all we have done for now is added more volatility to the market."
The Chicago Board of Trade most-active soybean contract was up 1.9 percent at $9.12 a bushel by 1155 GMT, after hitting its highest since mid-June at $9.23-3/4.
Corn and wheat drew strength from the soybean rally.
CBOT corn was up 1.1 percent at $3.81-3/4 a bushel, after earlier reaching a near four-month high at $3.85-1/4. Wheat added 0.9 percent to $5.20-1/2 a bushel following an earlier two-month top at $5.29-1/2.
The trade war between the two countries has drastically curbed US soybean exports to China, by far the world's biggest bean importer, and pushed down US prices.
After imposing retaliatory tariffs on US soybean imports, China has been taking mainly Brazilian beans, threatening to leave a bumper US harvest piled up in storage or rotting in fields.
Saturday's agreement could allow US soybean shipments to China to resume but it was unclear whether there would be a return to previous levels, analysts said.
"Given the temporary nature of the truce, I don't expect a bonanza purchase of 20 million tonnes of soybeans," said Michael Magdovitz, commodity analyst at Rabobank.
"I think it's more likely we'll see normal healthy monthly purchases of several million tonnes per month during the freeze period by the Chinese state to build up reserves."
The demand boost for US soybeans and other feed grains from the trade detente could be limited by an outbreak of African swine fever, which is reducing China's huge pig herd.