An assessment of soil and plant silicon levels in north Queensland

Sub-optimal levels of soil silicon (Si) can result in decreased cane and sugar yields. In general, soils of the wet tropics that have undergone significant weathering invariably have inherently low Si levels. To date, quantification of the Si status of soils in the northern sugar growing areas has not been undertaken. Using archival soil samples, an assessment of the Si status of soils of the Tully-Innisfail region of north Queensland was undertaken. In addition, the Si status of several old and new cane varieties was determined and estimates of net export of Si determined. The majority of the soil series found within this region were classified as having sub-optimal to marginal levels of Si for sugarcane production. Further, evidence is presented indicating declines in exchangeable cations and extractable Si with the establishment of a long-term sugarcane monoculture and a reversal in the Si trends when the monoculture is broken by rotation cropping. Significant genotypic differences between old and new varieties were observed suggesting that this may have been a result of breeding for lower fibre. It is suggested that targeted prophylactic applications of silicate-based materials on soils with sub-optimallevels of Si may significantly increase cane yields.