Nitrogen Level Impacting Fruit Yield and Quality of Mango in Northern Tropical Australia

Nitrogen (N) is vital for mango yield and fruit quality, but finding the optimal amount is crucial to avoid the 'stay green' problem, which diminishes both fruit quality and profitability. This study aimed to assess the impact of N levels on the fruit quality and yield of 'Kensington Pride' ('KP') mangoes and determine the amount of N that triggers the 'stay green' effect in fruit. A field trial was conducted in a commercial orchard with N treatments (0, 12.5, 25, and 50 kg ha-1) and four replications during the 2018 and 2019 cropping seasons. Fruit yield was quantified, and post-harvest quality (skin color during ripening, sugar content [degrees Brix], and texture) as well as ethylene effects were assessed. Fruit yields did not vary among N levels over the two cropping seasons but were significantly lower in 2018 (20.0 t ha-1) compared to 2019 (38.5 t ha-1), illustrating the alternate year-bearing habit of 'KP' mangoes. In the 2018 harvest, fruit from trees receiving 25 kg N ha-1 appeared yellow-green compared to those with less N, while fruit from trees with 50 kg N ha-1 exhibited 'stay green' skin, indicating that applications of 25 and 50 kg N ha-1 were excessive. There was no 'stay green' skin observed in the 2019 harvest, indicating that the environment may also be a contributing factor. The texture of ripe fruit from untreated control trees had the highest flesh resistance. Moreover, ethylene-treated fruit ripened in nine days post-harvest and had significantly lower sugar content than untreated fruit, which ripened in 14 days. This study provides valuable insights into the complex interactions among N application, fruit quality, and yield of 'KP' mangoes, highlighting the importance of appropriate N management for a sustainable and environmentally friendly commercial mango production system.