SAO PAULO, March 25 (Reuters) - Brazilian conglomerate Ultrapar has increased its stake in logistics firm Hidrovias do Brasil, it said late on Sunday, as part of a strategy to expand its footprint in businesses exposed to Brazil's agricultural sector.

Ultrapar agreed to buy a 16.88% stake in Hidrovias from Patria Investments and Temasek-controlled investment fund Sommerville, it said in a securities filing, raising its stake to 21.87%.

The deal was priced at 3.98 reais per share, an 11.8% premium over its Friday closing, valuing the transaction at 510.9 million reais ($102 million).

"Ultrapar plans to be a strategic and long-term reference shareholder of Hidrovias, supporting its growth, governance and management model," the conglomerate said.

"Hidrovias operates in a high-growth sector, considering the deficit of logistics infrastructure and the growing expansion of agribusiness, with complementary and synergistic operations to Ultrapar's portfolio."

($1 = 5.0021 reais) (Reporting by Gabriel Araujo; editing by Jason Neely)