Reducing nitrogen use under optimal irrigation and planting date can sustain sugarcane yield and gross margin under climate change

Sugarcane is a vital economic crop in Australia, supporting both agricultural and regional economies. However, its heavy reliance on high nitrogen (N) inputs raises costs and results in considerable losses to the environment. While climate warming is projected to enhance sugarcane yield in subtropical New South Wales (NSW), it remains unclear whether this benefit, combined with adaptive management, can sustain yields under reduced N use in future climates. To address this, the APSIM-Sugarcane model, validated with high accuracy (R²=0.82 for yield and 0.73 for gross margin), was driven by projections from 27 global climate models under two Shared Socio-economic Pathways (SSP2–4.5 and SSP5–8.5) to simulate yield responses to varying N rates, irrigation levels, and planting dates across the main production regions of Condong, Broadwater, and Harwood in northern coastal NSW. Results indicated that under future climates, yield and gross margin increased under current management practices, with further gains under optimal management (50 % PAWC irrigation and planting in September). The optimal strategy remained unchanged across N rates, but yield and gross margin declined with reduced inputs. The lowest feasible N rate under future climates sustaining current yield (101–127 t ha⁻¹) and gross margin (2147–3122 AU$ ha⁻¹) was 60 kg ha⁻¹ (a 40 % reduction from the current N rate of 100 kg ha⁻¹). At this level, irrigation was the primary driver of yield and gross margin, followed by temperature and CO₂. This study highlights practical nitrogen reduction strategies sustaining sugarcane productivity, profitability, and environmental sustainability under future climates in Australia.