Survey of nematodes in the Herbert region to develop a nematode-hazard index and evaluate soil health

Soil nematodes are microscopic worm-like organisms and are important members of the soil ecosystem. Some nematodes are either plant or animal parasites, and some are ‘free-living’ feeding on bacteria, fungi or on other nematodes. Plant-parasitic nematodes can cause significant yield loss in sugarcane. Free-living nematodes are vital contributors to soil health through their involvement in mobilisation of nitrogen and carbon and are important indicators of soil health. The objectives of this study were to determine the extent of plant-parasitic nematodes and their potential impact on sugarcane production in the Herbert region, and the use of nematode community analysis to determine the soil health of the surveyed sugarcane farms. Soil samples were collected from 56 locations from six sugarcane productivity zones, Central Herbert, Lower Herbert, Ingham Line, Stone River, Abergowrie and Wet Belt from one-year plant crops. Most of the sugarcane fields surveyed had medium (484 nematodes/200g soil) to high (1137 nematodes/200 g soil) numbers of root-lesion nematodes. Other nematodes, including root-knot nematodes, were relatively low in number. A nematode-hazard index (HI) was developed by adding the weighted number of parasitic nematodes determined from a hazard factor derived from the damage caused relative to damage caused by root-knot nematodes. Approximately 73% of surveyed farms had medium to high HI values, an indication of moderate to high potential impact on yield. As an indicator of soil health, soil food-web maturity indices (MI) were determined on the basis of nematode community. Analysis of nematode community showed low maturity indices (MI and MI2-5) (<3.5) in all farms, an indication of low soil food-web maturity and persistent use of chemical fertilisers. Soil food-web indices and metabolic footprints indices also indicated perturbation of sugarcane soil and a farming system dominated by herbivorous nematodes. Our study demonstrated that nematodes community analysis can be used as indicators of soil health for the sugar industry as well as a monitoring tool to determine the effects of management practices. Key words Sugarcane nematodes, nematode community analysis, soil health, soil food web, soil health indicator