GOOD-quality compost can boost soil and plant health, reduce water demand and combat plant diseases in horticulture and viticulture.

Other benefits include weed suppression and increased yields, says consultant Bill Grant.

Mr Grant, who is based at Castlemaine, is managing a project that has established eight field demonstration sites at vineyards, fruit orchards, an olive grove, a tomato farm and a cut-flower farm in central Victoria in the past six months.

"Composts work best where soils are poor and water is limited, so central Victoria is a perfect place to use them," Mr Grant said.

"Composted mulches and soil conditioners can improve farm productivity, but it is important to use the right product in the right way.

"Not all composts are the same."

Mr Grant said composts could be made on-farm or bought from commercial composters, but it was important to know what they were made from.

Commercial compost should only be bought from a business with certification in a quality management system and must have undergone heat treatment to sterilise weed seeds and kill plant diseases.

Compost should be a dark colour, moist and sweet smelling, with no unpleasant "off" or charred odours.

"The main thing is that it's not too young for what you're using it for," he said.

"If a compost is too young, it can have nutrient drawdown effects or even short-term toxic effects on plants, the same as manure might burn the roots of a plant."

Although commonly used by organic growers, Mr Grant said compost and compost teas were also useful for conventional producers.

Most of the growers taking part in the trials were not organic, although some farms were very intensive.

The Compost Users Group, an informal network allowing farmers, composters and researchers to exchange information, was launched at workshops held earlier this month at Harcourt, Murchison, Heathcote and Bendigo.

Data from the field trials will be available on a website and a series of field days is also proposed.