Optimising foliar nitrogen uptake of mango: effect of adjuvant, leaf position and time of potassium nitrate spray

Foliar application of potassium nitrate (KNO₃) is widely used in promoting flowering of mango trees, but the spray formulation varies greatly. We determined the effect of adjuvant, position of leaves and time of KNO₃ spray application on the leaf nitrogen (N) content of mango 'Kensington Pride' to identify optimum conditions for N uptake from foliar KNO₃. The treatments were spraying to run off 3% KNO₃ with 0, 100, 250 and 500 mL Li-700 100 L^‑1 solution on tagged mango leaves from the east (sunny side) and west (shaded portion) of trees in the morning (8:00 am) or night (8:00 pm) time. Each treatment combination was replicated five times and treated leaves were collected at 4, 12, 24, and 48 h after spraying (HAS), rinsed and analyzed for total N content. Results showed that total N contents were comparable in mango leaves across rates of adjuvant, time of application and location of the leaves at 4 and 12 HAS but varied significantly at 24, and 48 HAS. Leaf N content was higher in leaves that were sprayed with adjuvant than those without adjuvant and when the spray was applied in the evening. Total N content was also higher in leaves from the shaded part of the tree than those exposed to sunlight. The results indicate that addition of adjuvant and spray application in the evening assist N uptake of mango leaves following foliar application of KNO₃.