In 1999 the Natural Heritage Trust approved funding for a three year collaborative project between Tuckombil Landcare Inc and NSW Agriculture to investigate the impacts of horticultural chemicals and practices on soil health in the Northern Rivers of NSW and develop technologies to maintain economic and environmental sustainability in areas with degraded soil health.

A survey of 15 farms covering the macadamia, avocado, banana, coffee and sugarcane industries was conducted throughout 1999 and 2000 over 3 north coast catchments. This study measured soil health parameters such as microbial activity and biomass in soils, and chemical and physical attributes of the soils.

Results
It was demonstrated that a number of factors have led to the decline in soil microbial activity. These included increased bulk density, the lack of ground covers found under some crop management strategies (induced by herbicide use), and loss of organic material from soil. In addition, there were measurable declines in soil health when copper contamination was present. Copper contamination is a result of fungicide- derived copper application for pathogen control. Furthermore, it was shown that earthworms are strongly avoiding soils with copper contamination, even to quite low levels.

A soil earthworm survey was conducted in March, 2001. Analysis of results supports findings of previous research. Low worm numbers are found in orchard soils, whilst nearby control soils have greater numbers. In general, orchard soils were shown to have lower microbial biomass, greater bulk density and reduced water holding capacity, compared to nearby sites. Each of these factors may reduce the population of earthworms, and the lack of earthworms further reduces the breakdown of organic material and leads to a reduced soil structure and reduced soil quality.

Implications
The loss of soil health has implications for the economic and environmental sustainability of agricultural industries. For example, where soil health has been damaged through increased bulk density and decreased microbial activity, there is a greater likelihood that this soil will be prone to erosion. Once erosion occurs, an even greater decline in microbial activity is realised, as organic material and topsoil is lost from the site. Soils with reduced health are less likely to produce healthy crops, will require greater chemical and fertiliser inputs, and will be more prone to pathogenic invasion. Environmental implications of soil erosion include reduced dissolved oxygen in waterways and increased run-off of pesticides and nutrients.

Rehabilitation and remediation
Once soil erosion has occurred, rehabilitation technologies are required to stabilise the soil from further erosion, and to increase the microbial populations, which further improve the soil structure, fertility and crop health.

Already, results from the application of scientifically composted farm waste product from macadamia orchards to eroded areas has resulted in measurable increases in soil microbial activity and water holding capacity. Evidence also existed that the use of the compost on soil protected the soil layer from 2 major rainfall events. An increase in worm numbers was observed in the rehabilitated areas.

Healthy Soils in Macadamia Orchards

Fungicides and Soil Health

The Northern Rivers Soil Health Card

download Acrobat Reader for pdf files