BUENOS AIRES (Reuters) - Argentine farmers are likely to plant more soybeans in the current 2024/25 season, trimming the area dedicated to corn after that crop's last harvest was hit by a devastating insect plague and with rain forecasts looking rosier for soy.

The trend could see the largest expansion in soy planting in over a decade, analysts said, potentially boosting supplies globally with prices already subdued. Argentina is the world's top exporter of processed soymeal and oil.

The South American country's soy planting area has declined in recent years, competing with corn for space. But fears that a leafhopper plague like one that ravaged the last corn harvest could hit the fields again is likely to knock an estimated 2 million hectares (4.9 million acres) off corn planting - favoring soy.

"Of those 2 million hectares of corn not being planted, a large part will go to soybeans," said Cristian Russo, head of agricultural estimates at the Rosario grains exchange, which estimates 16.8 million hectares were planted with soy last year.

The Rosario exchange cut its 2024/25 corn planting area by 21% earlier this month but has not yet given an official soy planting area forecast. The rival Buenos Aires exchange cut the corn area by 17%. Corn planting begins next month.

Aníbal Córdoba, a farmer and member of a growers group present in northern provinces including Chaco and Santiago del Estero, said producers were building more soy into their plans.

"Our group usually plants 35% to 40% of our land with corn, but this time we're going to do an average 20-25%. Of what's not going to corn, almost all will be replaced with soy," he said.

TOUGH EQUATION FOR CORN; A BOOST FOR SOY

A jump for soy by anything near 2 million hectares could be the largest since a 1.2 million year-on-year increase in 2012, 1.4 million in 2008 or even 1.9 million hectares in 2003.

Fernando Flores, a farm technician and insect expert from farm town Marcos Juárez in Córdoba province, said the "shocking" corn losses last season due to the insect plague had put a lot of farmers off, though the very cold austral winter would have culled leafhopper numbers significantly.

"So perhaps the decline in corn planting may not be as dramatic as people think if it rains in September," he said.

Germán Heinzenknecht, meteorologist from the Applied Climatology Consulting Firm, however, said the outlook for early September remained dry, with more rain forecast for October, another incentive for soy whose planting starts that month.

"Soil moisture levels currently in a large part of the farming area, in the west and center, are not suitable for planting," Heinzenknecht said. "So the overall equation is tough for corn and a boost for soy."