Estimating Nitrogen Uptake Efficiency of Mango Varieties from Foliar KNO3 Application Using a 15N Tracer Technique

Commercial mango growers commonly spray potassium nitrate (KNO3) solution to enhance flowering and fruit quality, yet there is limited information on the uptake efficiency of nitrogen (N) by mango cultivars through leaf cuticles. The study aimed to assess N uptake efficiency (NUpE) from foliar application of KNO3 solution and compare NUpE among mango varieties. Mango cultivars were ‘Kensington Pride’ (‘KP’), ‘B74’ (‘Calypso®’), and ‘NMBP 1201’ (‘AhHa!®’), ‘NMBP 1243’ (‘Yess!®’), and ‘NMBP 4069’ (‘Now®’) grafted onto ‘KP’ seedlings. Leaves of six-month-old seedlings were dipped in 15N-enriched KNO3 solution and analyzed for total N and 15N contents. A significant correlation was observed between the leaf area and the amount of solution retained after dipping the leaves in the KNO3 solution. Moreover, leaves treated with the KNO3 solution had higher 15N levels than the natural 15N abundance, indicating successful N uptake from the KNO3 solution. The NUpE ranged from 27% to 44% and varied with variety. Cultivar ‘NMBP 4069’ had the highest NUE (44%) which was comparable with that of ‘B74’ (40%). ‘NMBP 1201’ showed the lowest (27%) NUpE which was comparable with that of ‘NMBP 1243’ (30%) and ‘KP’ (33%). These data on 15N uptake through the mango leaf cuticle demonstrates the effectiveness of foliar application as a method of supplying N to mango trees, highlighting important varietal differences in foliar 15N uptake efficiency. Considering these differences in NUpE among mango varieties will help in making informed decisions about cultivar selection and N management strategies for sustainable mango production.