Search

The effects of fulvic acid as a supplement to potassium (K) applications on mango fruit quality, flower synchronisation and yield were investigated in an 8-year-old 'Kensington Pride' (KP) orchard over two seasons, at Southedge Research Station in Far North Queensland, Australia. The aim of the trial was to determine whether fulvic acid (FA) improved the efficiency of potassium uptake. Experimental treatments included i) nil K + nil FA, ii) 800 g K tree-1, and iii) 800 g K + 300 mL FA tree-1. Treatments were applied approximately every 3 weeks, after fruit set and during the fruit filling stage through to harvest. Treatment effects were assessed by measuring tree yield, fruit weight, length, depth and width, the incidence of post-harvest disease, ground skin colour at eating-ripe stage, as well as the proportion of canopy flowering in different stages in the following season. Results indicated that neither K fertiliser nor FA increased average fruit number or yield. In the first year, K combined with FA significantly increased the proportion of fruit with no lenticel spotting and the lightness of the ground skin colour of eating-ripe mangoes. By the second season, K with or without FA significantly increased the average fruit length and foliar dry-matter K concentration, while fruit weight was only marginally increased when compared to the nil K treatment. In summary, the addition of K applied during fruit development led to improved fruit size and maintenance of foliar K concentrations 2 years after application. However, although the addition of FA with K fertiliser reduced the proportion of fruit with lenticel spotting, this result was only observed in the first season of the trial and hence would require further research to confirm.

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.

Productivity in temperate tree crops such as apple has been lifted several-fold by research focusing on optimising a combination of canopy components including light relations, vigour control, tree architecture and crop load. This paper outlines the research behind the Small Tree-High Productivity Initiative (STHPI), which is focused on improving productivity of mango, avocado and macadamia. Preliminary results from work we are undertaking for each of the above canopy components in mango will be outlined. A rootstock screening trial to identify vigour-managing, high-productivity rootstocks is being undertaken, and we present a comparison of the best-performing low-medium vigour rootstock varieties compared with control 'Kensington Pride' (KP) rootstock at 6 months old. Comparisons between 'Keitt', 'NMBP 1243' and 'Calypso' scion cultivars with regard to tree diameter, height and canopy growth at different orchard densities and training systems will also be presented. Preliminary results from an orchard light-relations study indicate that mango yields continued to increase with light interception up to 50%, and reached a maximum of 20-30 t ha-1 at 68% light interception in KP trees approximately 25 years old. In a crop load trial, inflorescence thinning in a 'Calypso' orchard did not significantly reduce yields when up to 90% of inflorescences were removed, but did when 95% of inflorescences were removed, as trees were unable to compensate by adjusting fruit set, size and yield. Inflorescence thinning beyond 80% increased the number of fruit set per panicle, and thinning up to and including 90% of inflorescences increased fruit weight from 340 g to ›400 g per fruit. This project is still in its initial stages; however, early indications suggest there may be opportunities to improve early orchard yields through optimising light interception in an orchard's life, potentially through the use of higher densities, and that rootstocks and tree training methods, once identified, may help in the management of vigour. It is also hoped to obtain a better understanding of how crop load influences the balance between vegetative growth, flowering, fruiting, alternate bearing and fruit quality.