A moisture retention system for grain crops was the subject of a trial that generated considerable interest among farmers and researchers at the Birchip Cropping Group's (BCG) main field day last week.

The system involves covering cereal crops in a thin, clear UV-degradable polyethylene film (with the edges buried in the soil between crop rows to seal it) similar to the plastic wraps commonly used in Australian households. The film, called Xtend, was developed by a company called Integrated Packing.

The main object of wrapping the crop is to retain moisture that would otherwise be unavailable to the plant because of transpiration and evaporation. It may be possible that the amount of water available to a cereal plant could be increased by a factor of three using the system.

The Birchip trial, which is a joint project of BCG and the Cooperative Research Centre (CRC) for Polymers, involved a wheat crop planted on June 18 and immediately covered with the film, and a control crop left uncovered. The film - about half the thickness of a household plastic wrap - was removed on September 18.

BCG chairman Ian McClelland watched the trial with interest as the wheat plants germinated and grew, stretching the film and leaving beaded moisture on the inside which trickled down back into the soil where it could used again and again. Although the covered crop developed later than the control, it grew a great deal more in three months after sowing.

Growers at the field day also heard that the system had other benefits such as possibly retaining heat around the crop in the winter, and acting as a barrier to airborne diseases or fungal spores.

A system has already been developed to sow a crop and cover it with film at the same time, but a key challenge will be to control the rate at which the film degrades under UV light so that time and expense is not required to remove it. Ideally, it would degrade sufficiently before rising spring temperatures made it too hot under the film for the crop to survive. Unlike the maize crops with which the Xtend system has been trialed overseas, cereal crops won't be able to break through the film on their own. The film must also degrade sufficiently in contact with the soil.

Another important challenge will be to make the system affordable, or to ensure that using the system increases yields to the point where it is profitable. At six microns thickness, the film costs $250 per hectare however Integrated Packing's Peter Johnstone says researchers are developing a thinner film that would reduce costs over time.