Effect of Alternate Bearing Phenomenon and Boron Foliar Application on Nitrogen-15 Uptake, Translocation and Distribution in Mango Tree (cv. Zebda)

The objectives of this investigation are to study nitrogen uptake, translocation, accumulation and distribution in mango tree organs using labeled nitrogen (15N) and to understand the mechanism of boron action in increasing fruit yield in the off-year. A field experiment was conducted using fifteen-year-old mango trees (cv. Zebda) grown at Al Malak Valley Farm, El-Sharkeya Governorate-Egypt. Treatments included the application of (15NH4)2SO4, “in the on-year”, at a rate of 50 g nitrogen/tree through the stem injection technique. While boron was sprayed on the same trees “in the off-year” at the following rates: 0.0 (control), 250 and 500 mg·L–1. The authors hypothesize that boron and nitrogen act synergistically to increase mango fruit yield in the off-year. Results indicated that the highest 15N uptake and accumulation in the on and off-years was observed in the upper (young leaves). When boron was applied at 250 mg·L–1, in the off-year, the upper (young leaves) recorded the highest 15N uptake and accumulation (%15Ndff = 13.93) relative to the other two leaf categories and those of the on-year. In the on-year fruit accumulated higher 15N than leaf or bud. In the off-year, bud exhibited the highest 15N accumulation without boron application, while leaves exhibited the highest 15N with boron application. The highest %15Ndff in all tree organs was observed at 250 mg·L–1 boron rate. Boron increased nitrogen uptake, translocation and accumulation in mango tree organs. A synergistic relationship was observed between boron and nitrogen which led to an increase in fruit yield in the off-year.