Aussie farmers can now use a new, free, smartphone app developed by the CSIRO to help them make crop and paddock-management decisions.

In what's been hailed as an Australian first, Graincast uses information from satellites, climate forecasts and sensors to forecast grain yield.

CSIRO scientist Dr Roger Lawes said growers only need to enter the paddock they want to be analysed; the crop grown last season; and the crop they are planning to grow in the current season into the app.

"Having a yield forecast can help farmers with crop input management, setting yield targets, diagnosing yield constraints, risk management, marketing decisions, forward selling and more," Dr Lawes said in a statement on Thursday.

The new innovation is the only one of its kind that provides immediate soil, water and yield information at any time without the need for farmers to input substantial information about their paddock.

The free app was created by CSIRO scientists following feedback from grain growers about their experience and needs.