Sugarcane was first planted in Australia during the 1880s and within a few years, soil health problems were apparent. Technical papers published between 1900 and 1938 indicated that a ‘sick soil’ syndrome was widespread and seemed to be associated with continuous monoculture and depletion of soil organic matter. When mechanical harvesting was introduced in the 1960s, soil health problems worsened because the soil was compacted due to mismatched wheel and row spacings. Productivity ( ugar yield per harvested hectare) reached a plateau between 1970 and 1990 and this prompted the industry to establish a multi-disciplinary research team (the Sugar Yield Decline Joint Venture) to find solutions to the yield decline problem. Following 10 years of research, a new farming system was developed that incorporated the following practices: 1) permanent raised beds maintained through traffic control; 2) a direct-drilled legume grown in rotation after the sugarcane was terminated with herbicide; 3) ouble-disc openers used to replant sugarcane with minimal soil disturbance; and 4) sugarcane harvested green with a cover of plant residues (the trash blanket) permanently maintained on the soil surface. Recent research has focused on the benefits obtained from this farming system. Surveys have shown that root biomass is greatest in the upper part of the soil profile where soil carbon levels are highest (i.e. the soil immediately below the trash blanket). These surface roots are also quite healthy, harbour ng 55-70% fewer Pratylenchus zeae and Meloidogyne spp. than roots further down the profile. Pot experiments in which sugarcane was grown in soils collected from different depths confirmed the observations made in the field. Plants grew much better in surface soils, with aboveground biomass 35-100% higher than in soils from depths of 2.5-10 cm. The soil’s carbon status also had a huge impact on populations of P. zeae in roots. In sandy loam soils, for example, an increase in soil carbon levels from 1% to 1 5% resulted in numbers of lesion nematodes being reduced by about 80% (from more than 21,000 nematodes/g dry weight of root to about 4,000). Soil microarthropods appear to be contributing to this effect, as more than 30 predatory species have been found in well-managed sugarcane soils. Some mites fed voraciously on nematodes in the laboratory and an initial experiment in pots showed that a species of Protogamasellus reduced populations of Tylenchorhynchus annulatus, P. zeae and microbivorous nematodes by 9 , 70 and 70%, respectively. A third tier of research aims to determine whether Pasteuria, a bacterial parasite of nematodes, is having an impact on nematode populations. Pasteuria endospores have been seen on Meloidogyne javanica, Helicotylenchus dihystera, P. zeae and T. annulatus and a number of sites with relatively high infestation levels have been identified. The effects of natural and introduced infestations of Pasteuria are currently being studied.
Joint Meeting of the 2016 Society of Nematologists and the Organization of Nematologists of Tropical America (ONTA), Montreal, Canada 17-21 July 2016
Journal of Nematology / Vol. 48, No. 4, pp.372-373