The relationships between organic matter inputs and changes in soil properties were investigated in irrigated cropping regions of Victoria and New South Wales.

The trials involved the use of irrigated grain growers' paired paddocks, with each pair consisting of one paddock with a relatively higher organic matter throughput scenario and a paddock with a lower organic matter throughput scenario.

The results showed that in most of the paired paddocks the system with higher organic matter throughput produced yields equal to or higher than its adjacent paddock with lower throughput.

"It's not scientific proof, but this data nevertheless constitutes convincing evidence for growers," DPI researcher Dr Peter Fisher said.

Dr Fisher said the project aimed to address growers' concerns about declining soil structure resulting from continuous cropping.

"Soil structural decline under cropping systems is something that many farmers are familiar with," he said.

"Soil structural degradation probably remains, after salinity, the major threat to the sustainability of agricultural production.

"It is commonly associated with soil hardness, poor germination, restricted root growth, poor water infiltration, reduced water holding capacity and inevitably, reduced yields."

Dr Fisher said soil organic carbon was important in building and maintaining good soil structure, but a lack of understanding about the processes involved and a lack of experimental evidence in Australian conditions about the benefits had left advisers and agronomists wary about making recommendations to growers to increase organic matter inputs.

"This project has developed a better understanding of how varying organic matter inputs influences soil organic carbon, and how soil organic carbon influences other soil properties and ultimately crop performance," he said.