SAO PAULO, Jan 30 (Reuters) - Brazil and Bolivia will carry out studies on building fertilizer factories in both countries, which could help reduce their dependence on imported fertilizers, Brazil's agriculture ministry said on Tuesday.

The South American nations signed agreements which commit to studying possible new plants to manufacture nitrogen, phosphate and potassium fertilizers, the Brazilian ministry said in a statement.

Brazil, an agricultural powerhouse and the world's biggest soybean producer, imports the vast majority of its fertilizers while Bolivia is one of Brazil's key suppliers of natural gas, an ingredient for nitrogen fertilizers.

The deal should help decrease Brazil's dependence on imported fertilizers, the country's Agriculture Minister Carlos Favaro said in the statement.

"Alternatives need to be created, one of which is the supply of natural gas at more competitive prices," he said.

Favaro added that Brazil intends to complete its current fertilizer projects, including a plant in Tres Lagoas, a city in Mato Grosso do Sul, a key farming state which borders Bolivia.

Construction on the Petrobras-led project was halted in 2014, when works were about 80% complete, and the firm has for years tried to sell it off. Executives from the state-run oil firm said last year they intend to finish construction.

The agreements, which commit both Brazil and Bolivia to undertaking studies for the new plants, will expire in five years but can be renewed, the statement said. (Reporting by Andre Romani; Editing by Sonali Paul)