Former President Luiz Inacio Lula da Silva is luring allies from Brazil's powerhouse farm sector to his presidential campaign, looking to fracture his rival's base in a move that risks tensions with his own environmentalist supporters.

Agribusiness made big strides under Lula's 2003-2010 government, but right-wing President Jair Bolsonaro has made a powerful connection with rural interests, vowing to push Brazil's farming frontier deeper into the Amazon rainforest.

In contrast, Lula has promised "net zero deforestation" in Brazil within four years, bringing his rhetoric in line with greener thinking in Latin America's leftist circles.

Still, in the capital Brasilia last week, Lula raised eyebrows by shoring up relationships with traditional farming interests, endorsing a Senate run by lawmaker Neri Geller, vice-president of the congressional farm caucus, and meeting with Senator Carlos Favaro, who also has strong agribusiness ties.

Geller, who was farm minister under Lula's chosen successor Dilma Rousseff, told Reuters he saw more farm industry allies coming out for him, including Brazil's "Soy King" Blairo Maggi, another ex-farm minister criticised as an apologist for deforestation.

Despite Lula's double-digit lead over Bolsonaro ahead of the October election, many big names in agribusiness remain shy about talks with the leftist leader. Several farm industry leaders declined to answer Reuters' questions about their conversations with the Lula campaign.

After meeting with Lula, Geller and Favaro took heat from a farm lobby group in their home state Mato Grosso, highlighting the hazards of breaking with Bolsonaro in farm country.

Lula also got blowback from the left over the meetings. Green advocates distrust Geller for trying to loosen environmental licensing and Favaro for pushing a bill to buy time for farmers and ranchers accused of invading public lands.

Lula's former Environment Minister Marina Silva told newspaper Folha de S.Paulo that alliances with lawmakers such as Geller and Favaro would "maintain the country's status as environmental pariah."

Another former environment minister, Izabella Teixeira, who has helped to put together Lula's government program, took a more pragmatic view.

"First you have to win the election, and these are arrangements that make the election viable," she told Reuters. "Another thing will be politics after the election."