UPDATE 2-Vale to rent potassium assets from Petrobras

* Lease may pave way for development of Carnalita play

* Iron-ore miner Vale aims to bolster fertilizer business

* Top grains producer Brazil hungry for cheaper fertilizer

SAO PAULO, Feb 9 (Reuters) - Brazilian miner Vale is moving closer to developing the Carnalita potassium project in northeastern Brazil after agreeing to rent mining assets from state-controlled oil giant Petrobras , according to a securities filing on Thursday.

The development of the Carnalita project and other assets in that area aims to satisfy growing demand for one of the three key soil nutrients in Brazil, the world's biggest exporter of coffee, orange juice and sugar and second largest exporter of soybeans.

Brazil must import about 90 percent of its potassium, or "potash" needs, much of it from places as far away as Canada, Belarus and Jordan. After arriving in local ports it must be hauled long distances to agricultural regions at great expense.

Brazil's government is reforming its mining code in part to make it easier to increase potash production and reduce the country's dependence on imports.

The new project needs approval from Vale's board of directors. Vale is the world's top iron-ore and nickel producer and is expanding into the fertilizer business with a potash project in Argentina and nitrates mine in Peru.

Petrobras rented the mining rights in that area in Brazil's northeastern state of Sergipe for 30 years.