On the property of lupin pioneer Graeme Preston, the crop is proof that the narrow leaf white lupin is the legume vehicle for sustainable cropping on light land that will economically sustain a cereal-lupin rotation.

Mr Preston, with his sons Murray and David, say one 200ha paddock, known as 1A Block which has been continuously cropped to wheat and lupins for 42 years, shows no sign of disease or declining yields.

It is regarded as the longest wheat-lupin rotation ever recorded in any lupin-growing area in the world.

Most of the Prestons' farm follows a similar rotation with the long-term yield average for wheat nudging 3t/ha and more than 2t/ha for lupins.

The best crops recorded were 4t/ha for wheat and 3.4t/ha for lupins.

"We're not saying this type of rotation suits everybody," Graeme Preston said.

"This is what has happened on Muranda Plains which is a no stock operation.

"But I believe lupins, where they can be grown economically, form an integral part of a sustainable farming system."