Impact on crop performance of application timing of nitrogen fertiliser and interaction with harvest time

In the Wet Tropics, fertilisation of early-harvested crops is often delayed as ratoons are slower growing and growers focus on land preparation, sugarcane planting operations and early crop establishment. However, as the harvest season progresses and the risk of experiencing high rainfall increases, fertilisation often occurs immediately behind the harvester. A trial was established on a clay loam soil at Tully to explore the impact of nitrogen (N) fertiliser application timing on a range of crop traits including N uptake, yield, and nitrogen-use efficiency (NUE). Treatments included three different application times (3-, 6- and 8-weeks post-harvest) and four N application rates (0, 80, 130 and 180 kg N/ha). An additional treatment (harvest time) was established in the second-ratoon crop. This allowed the effect of fertiliser application time to be assessed for ratoon crops established at different times of the harvest season (e.g, early versus late). There were statistically significant differences in crop traits associated with N rate and the timing of fertiliser application. For the early-harvested crop, there were no adverse effects on yields or NUE from delaying N fertiliser application up to 8 weeks after harvest. There was no statistically significant difference in yield or crop N uptake for fertiliser application timing in the late-harvested crop. The outcome of this research supports existing grower practices in the Wet Tropics region whereby fertiliser application is often delayed to crops harvested early in the season but applied immediately after harvesting crops ratooned late in the season.