When is the best time to apply postharvest nitrogen fertiliser?

The effect of application timing of nitrogen to mango trees was investigated over 3 years to determine whether pre-harvest applications of N affected fruit quality, canopy growth, flowering and tree yield in 8-year-old 'Kensington Pride' (KP) and 'R2E2' mango trees growing in Far North Queensland. The experiment consisted of six treatments, where a total of 156 g N tree-1 was applied as 340 g urea at different application times and proportions. The treatments were applied as: 1) 100% postharvest at 2 weeks postharvest (control), 2) 50% 2 weeks pre-harvest plus 50% 2 weeks postharvest, 3) 35% 2 weeks pre-harvest plus 65% 2 weeks postharvest, 4) 65% 2 weeks pre-harvest plus 35% 2 weeks postharvest, 5) 35% 4 weeks pre-harvest plus 65% 2 weeks postharvest, and 6) 65% 4 weeks pre-harvest plus 35% 2 weeks postharvest. The results indicated that the pre-harvest applications of N did not significantly affect tree or orchard yield, fruit weight, size or number, nor did they negatively influence background skin colour or disease incidence at eating ripe in either cultivar, when compared with the control (100% N added postharvest). In the 'R2E2' trees, treatments 4 and 6 had an increased total panicle count. For the KP trees, pre-harvest applications of N in treatments 5, 6, 4 and 2 had increased stages of floral development when compared with the control trees, at the early stages of flowering. These results indicate that applications of N fertiliser prior to harvest can positively influence seasonal vegetative growth and early inflorescence development, but responses are cultivar specific. Therefore, N fertiliser applications can be added prior to harvest to encourage rapid floral and vegetative development after pruning without negative effects on fruit quality, particularly if N is applied as split applications at the recommended rate for tree size and cultivar.