Three months out from planting, soybean growers in southern NSW have jumped at the spike in local feed grade prices.

Some have locked in early contracts, despite limited access to irrigation water.

A Griffith buyer has offered $600 a tonne for feed grade soybeans up $120 a tonne on the same time last year.

Coleambally grower Ken Brain says it was an offer too good to refuse.

"At the moment, I've been crunching numbers against rice and the price of beans is pretty good."

Yenda irrigator Paul moon grows corn, rice and soybeans in his summer cropping program.

He's debating whether to sign soybean contracts now, given the high price for temporary water.

"They price they've put out is a fantastic price and a lot of our scenario will base itself around the water market," he says.

"Since the inter-valley trade has closed, its driven the water price up.

"Unless it gets sub $50 a megalitre, it can be a lot of work for no reward."