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* Uncertainty about the prospect of a trade deal between the United States and China kept gains in check, traders said.
* The benchmark Chicago Board of Trade (CBOT) May soybean futures contract broke through technical resistance at the low end of its 20-day Bollinger range.
* Soymeal and soyoil futures also posted higher closes.
* The higher close in soyoil futures marked its first day of gains since Feb. 28.
* Private analytics firm IEG Vantage trimmed its forecast for 2019 US soybean plantings to 85.494 million acres from 86.044 million acres.