A LIBERAL National Party government would spend $4.6 million on research to gain greater productivity in Queensland's sugar industry.

The party has promised that if elected on March 24, it will double agricultural production by 2040.

LNP leader Campbell Newman was in Mackay, where he visited a sugar cane farm and helped plough a legume crop into the ground for soil improvement.

He said sugar was Queensland's second-largest agricultural commodity, generating $1.3 billion for the state's economy each year.

The $4.6 million would be spent over four years, Mr Newman said.

"This is a real commitment to support the growth of the sugar industry and the families and the communities that the industry supports," he said.