THE world needs to start planning now if it is to avoid global food shortages.

Scientist and author Prof Julian Cribb predicts the world will run out of food if wastage and population growth continue.

He will tell farmers at the annual conference of the Grasslands Society of Southern Australia next month they will have to double their food output by 2050 using less land, water, energy and nutrients.

The good news is grazing industries and the world's grasslands will play a vital role in meeting the global food challenge, Prof Cribb said.

But it would mean re-thinking the way food is produced.

"We need to start spending a lot more now on research and development so the world's 1.8 billion farmers will have a chance to meet these challenges," Prof Cribb said.

"We need new energy systems for agriculture as fossil fuels run out or simply become too expensive.

"We need to convince everyone living in cities to recycle water and nutrients."

If that happened there would be plenty of both for agriculture.

Prof Cribb said the world would also need to rethink its diet.

"In future, the 10 billion inhabitants of the earth will eat less energy-rich diets and more vegetables," he said. This means that naturally grown, healthy meat from the world's grasslands and rangelands will be much more expensive and give a better return to the grower than it does today."

Prof Cribb is one of more than 20 guest speakers at the GSSA's conference at the Wangaratta Performing Arts Centre on August 10-12.