Department of Plant Sciences

N fertiliser management is increasingly important in sugarcane crop as imperatives to reduce environmental impacts of N escalate. In this paper we report testing of a new concept for N management in sugarcane, the N Replacement system. This system aligns N applications with actual cane production, rather than potential production, by relying on soil N reserves to buffer differences in crop N needs and N fertiliser supply in individual crops. In 11 experiments that were conducted over an average of three crops, yields in the N Replacement treatment were similar to those achieved with the farmers’ conventional N management that had average N applications 18 to 157 kg/ha/crop greater than in the N Replacement treatments. The crop N surplus, an estimate of N potentially lost to the environment, was ~40% lower in the N replacement treatments compared with conventional N management. N concentrations and N uptake in cane for most crops were lower than those previously reported. These low N concentrations may be a response to the lower N application, and explain why yields were maintained in the N Replacement system at the lower N rates. The results show that the ecologically-based N Replacement system may deliver superior environmental outcomes without significantly reducing production. The results also show that predicting yield of the coming crop, a common basis for N management, is not necessary in sugarcane N management, provided N applications and production are matched in the longer term.