INTERCROPPING SUGARCANE WITH SUNFLOWER AND MIXTURES OF PLANT SPECIES: EFFECTS ON THE SOIL BIOLOGICAL COMMUNITY

SOME SUGARCANE GROWERS in Australia have attempted to improve the health of their soils by adopting best-practice farming systems. However, soil biological health remains relatively poor, largely because levels of soil organic matter are more than 50% lower than attainable levels and the soil biological community is dominated by pests and pathogens. Intercropping sugarcane with various plant species is one option being investigated to improve the situation and results from two trials are reported here. Nematodes were used as a biological indicator and, in a trial in which a mixture of four and eight plant species was sown immediately after harvest and grown for 10?12 weeks, intercropping generally reduced populations of plant-parasitic nematodes and increased populations of free-living nematodes. The 8-species mix grown for three successive years increased soil carbon levels by about 15% and, although this effect was not statistically significant (P = 0.086), the nematode and carbon results suggest that long-term benefits are likely to be obtained by incorporating intercropping into the sugarcane farming system. Sunflower was the intercrop species in the second trial and root colonisation and DNA tests for arbuscular mycorrhizal fungi showed that sugarcane roots associated with sunflower roots were more heavily colonised and supported a more a diverse range of these fungi than roots from an adjacent site that was not intercropped. Collectively, these results suggest that intercropping improves the biological health of sugarcane soils. However, long-term field trials are required to substantiate the benefits obtained; assess the impact of intercropping on sugarcane yield; confirm that intercropping improves soil carbon levels; and fully evaluate its effects on soil biodiversity.