Management practices to improve soil health and reduce the effects of detrimental soil biota associated with yield decline of sugarcane in Queensland, Australia

Yield decline (YD) of sugarcane is a widespread problem throughout the Australian sugar industry. It is defined as “the loss of productive capacity of sugarcane-growing soil under long-term monoculture”. Factors contributing to YD are the monoculture itself, excessive tillage of the soil at planting and severe soil compaction resulting from the use of heavy machinery during the harvesting operation. Collectively, these crop management practices have led to the development of sugarcane-growing soils that are low in organic C and cation exchange capacity, have a high bulk density and have a low microbial biomass. This in turn is associated with a build up of populations of detrimental soil organisms, which affect the growth and health of the sugarcane root system. Significant yield increases have been demonstrated following pasteurization or fumigation of the soil or treatment of the soil with fungicides or nematicides. Several detrimental soil organisms associated with YD have been identified, including a fungal root pathogen (Pachymetra chaunorhiza) and the lesion nematode (Pratylenchus zeae). Experimental evidence, however, suggests there are many other unidentified detrimental soil organisms associated with YD.

In order to circumvent YD, major changes to the cane cropping system need to be considered. Different rotation breaks (sown pasture, alternate crops, bare fallow) were evaluated for their impact on soil health and the composition of the community of organisms in soil previously under cane monoculture. Despite the breaks having different effects on populations of beneficial soil biota, all breaks reduced populations of known detrimental soil biota and significantly increased the yield of the following cane crop. A single legume-based break crop appeared to be sufficient to capture the majority of these benefits. Other possible management options including the use of organic amendments and minimum tillage techniques are discussed.