The question that drove a three-year Action on the Ground project: Can organic N sources be used to reduce fertiliser N rates whilst reducing GHG emissions from landfill, while also enhancing soil carbon and long-term productivity?

Three demonstration trials in sugarcane and macadamia and a replicated scientific trial in sugarcane were undertaken on the Sunshine Coast to assess the potential of partially replacing mineral N fertilizer with compost and a biological nitrogen fixing product, and to determine the degree to which such practices can reduce GHG.

In cane, both replicated and demonstration trials showed that application of compost above or below the trash blanket can partially substitute the use of mineral fertilizer. There was no consistency of significant impact of compost in reducing nitrous oxide emissions. Avoiding application of N in excess of recommended rates (165 kg/ha) was more effective than partially substituting mineral N fertilizer with compost in minimizing nitrous oxide emissions.

On macadamias, both trials showed that application of compost and the biological N fixing agent can partially substitute the use of mineral fertilizer. Over the trial period, N fertilizer application rates were reduced by 80 kg N ha^-1 with compost alone, and by 170 g N ha^-1 where compost was used in combination with N-fixing microbes.

Though not a specific aim of the project, a finding of the project was that compost application in macadamias re-established the Ap-layer being a surface feeder, and this significantly reduced erosion in  high rainfall events, thereby building resilience in the orchard.