When is the best time to apply postharvest nitrogen fertiliser?

Abstract

The effect of application timing of nitrogen to mango trees was investigated over 3 years to determine if 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 per tree was applied as 340 grams of urea at different application times and proportions. The treatments were applied as 1) 100% post-harvest (control), 2) 50% 2 weeks preharvest plus 50% 2 weeks post-harvest, 3) 35% 2 weeks pre-harvest plus 65% 2 weeks post-harvest, 4) 65% 2 weeks pre-harvest plus 35% 2 weeks post-harvest, 5) 35% 4 weeks pre-harvest plus 65% 4 weeks post-harvest, and 6) 65% 4 weeks pre-harvest plus 35% 4 weeks post-harvest. 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 it negatively influence background skin colour or disease incidence at eating ripe in either variety, when compared to the control (100% N added post-harvest). 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 to the control trees, at the early stages of flowering. These results indicate applications of N fertiliser prior to harvest can positively influence seasonal vegetative growth and early inflorescence development but responses are variety 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 variety.