Effect of Potassium Nitrate Spray on the Flowering and Fruiting of Mango Varieties Grown in Uganda

Aims: To evaluate the effect of potassium nitrate (KNO3) on flowering and fruiting of mangoes in Uganda.

Study Design: Randomized complete block design in a split plot arrangement.

Place and Duration of Study: National Crops Resources Research Institute Namulonge, National Semi–Arid Resources Research Institute in Serere and Bulindi Zonal Agricultural Research and Development Institute in Hoima in 2015 and 2016.

Methodology: The study was superimposed on eight-year-old mango orchards which were simultaneously planted at the three sites. Main plot treatments comprised three mango varieties (Bire, Tommy Atkins, Zillate), while sub-plot treatments comprised four concentrations of KNO3 (zero as control, 1, 2 and 4%). Data was collected on number of terminal buds induced after applying KNO3, percentage flowering, number of fruits set per 20 panicles and fruit yield per tree.

Results: Trees sprayed with KNO3 produced higher (P < .05) numbers of terminal buds than the control. Across sites, Bire produced higher numbers of buds (64.8) than Tommy Atkins (46.3) and Zillate (17.8). Flowering response was higher in Bire (28.6%) than in Tommy Atkins (20.8%) and Zillate (17.8%). Flowering response of trees sprayed with 2% KNO3 (31.4%) was higher than that of trees sprayed with 1% KNO3 (24.7%). Mean number of fruits induced per 20 panicles in trees sprayed with 4% KNO3 (8.24) was higher than that of trees sprayed with 1% KNO3 (4.8). Fruit yield of Tommy Atkins (23.01 kg/tree) was higher than that of Bire (10.97 kg/tree). Mean fruit yield of trees sprayed with 2% KNO3 (27.36 kg/tree) was higher than that of trees sprayed with 1% KNO3 (15.93 kg/tree).

Conclusion: For better fruit yields, farmers at Bulindi should grow Tommy Atkins and apply 2% KNO3. Farmers at Namulonge can grow any of the three mango varieties and apply 2 or 4% KNO3, while those at Serere can grow Tommy Atkins and Zillate, and should apply 4% KNO3.