This project was investigating the reasons for diminished root and soil health in tomato and melon cropping systems. The project consisted of two main research themes, including (1) the effects of organic amendments on the physical, chemical, and biological properties of the soil and the interaction with root disease organisms, and (2) assessment of a broad range of commercially available bio-additive products claimed to increase yield and improve soil health.

Field trials conducted at Bundaberg and Bowen showed that a yearly input of up to 34 tonnes of carbon per ha per year (in the form of sugar cane trash, a green manure crop, and/ or molasses), greatly augmented the soil microbial populations. However, the marketable yield of the tomato and melon crops was not increased, and in some seasons, decreased slightly. Molasses was shown to have a variable benefit in stimulating soil microbes. It was suspected that the yield depression from addition of the organic amendment treatments for some crops grown in the trials was due to a nitrogen (N) draw-down effect. The N draw-down in crops grown in soil to which organic matter is applied could be overcome by applying soluble N fertiliser through the trickle irrigation tubing in the first 2 weeks after transplanting or allowing a period of at least 13 weeks from incorporation to field planting. Studies of the effects of the organic matter treatments on tomato stem pathogens Fusarium spp. and Verticillium spp. (fungi capable of vascular invasion via the roots and in some cases may be pathogenic and cause wilt diseases depending on the species and strains involved) revealed inconclusive results.

Comprehensive testing of a broad range of commercially available bio-additive products (including E2001/ Multibacter, Trichogrow/ Trichoflow, various Nutri-Tech Solutions products, Humega/ SupaHumus, and Kelpak) showed that Kelpak was ranked in the top 2 treatments for weight of marketable fruit in 5 of the 6 trials. However, differences were only significant for the 2001 tomato trial at Bowen, and then only between Kelpak and Supa Humus. This lack of difference between treatments for the yield and quality parameters that were measured indicated that growers using these products would be unlikely to see any visible effects to the crop. Despite anecdotal evidence aplenty, the absence of comprehensive field studies on bio-additive products of the kind undertaken in this project can be explained by the quantity and meticulous nature of the work required to conduct such experiments. The fact that our team conducted the work at 2 geographically diverse sites makes the work even more extraordinary.

This project has been funded by Hort Innovation, using the research and development levies listed below and contributions from the Australian Government. Hort Innovation is the grower-owned, not-for-profit research and development corporation for Australian horticulture.

• Vegetable Fund