Effect of breaks and nitrogen fertiliser on shoot development, maintenance, and cane yield in an irrigated plant crop of Q117

A rotation experiment established at the BSES Sugar Experiment Station in the Burdekin in 1994 was returned to sugarcane in late August 1998, The experiment comprised six pre-history treatments, three of which were continual sugarcane with either trash retained, trash removed, and trash removed plus fumigation immediately prior to returning to sugarcane, The other three treatments were 42 month breaks of other crops, pasture, or bare fallow. All pre-history treatments were split to four rates of nitrogen fertiliser - 0, 50 kglha basal, 50 basal plus 130 kglha at 90 days after planting, and 0 basal plus 180 kglha at 90 days. Shoot and stalk development and maintenance, and crop yield were measured. There was no yield difference between any of the breaks and fumigated continual sugarcane, but these treatments outyielded continual sugarcane by around 30 tlha or 26%. There was no response to nitrogen fertiliser following crop, bare fallow or fumigated sugarcane pre-histories, but a significant response following continual sugarcane and pasture pre-histories. The basis of the yield response was established during early shoot development. Initial primary shoot development was independent of available nitrogen (soil + fertiliser) but secondary tiIIering was strongly influenced by available nitrogen. In addition, shoot retention was improved with enhanced nitrogen status. The yield differential between break pre-histories and continual sugarcane ranged from 48% when no nitrogen was applied to 13% at the maximum nitrogen rate of 180 kglha. It is suggested that, in a system with high inputs of radiation, water and nitrogen, there is likely to be a relatively limited expression of the yield decline phenomena.