Effect of breaks from sugarcane monoculture and biocides on the growth and yield of a subsequent sugarcane crop.

Plots of continual sugarcane (plough-out/re-plant or PO/RP), and 54 month pasture, crop and bare fallow (BF) breaks were split to six biocide treatments prior to re-planting to sugarcane. The biocide treatments were control, fumigated, nematicide applied twice or four times, fungicide, and fungicide plus nematicide. There was no significant difference in yield between the different breaks but they out-yielded PO/RP by around 20%. Similar yields were achieved with fumigation, fungicide and fungicide plus nematicide but all three significantly out-yielded the control and both nematicide treatments. Nematicides alone produced a similar yield to the control. However, nematicides had a synergistic effect in combination with fungicide. The unfumigated crop and pasture breaks produced yields similar to fumigated PO/RP. However, there was a further response to fumigating crop, pasture and BF breaks, possibly due to either detrimental biota remaining in the soil following the breaks, nutritional differences created by the breaks or a combination of both. The results indicate that the percent increase in yield from fumigation can be re-produced by the combination of fungicide and nematicide following PO/RP and BF but not following crop or pasture breaks.