Effects of Boron and Silicon Application on Concentration and Distribution of Macronutrients in Different Tissues of Mango Seedlings

Due to recent drought periods in Hormozgan province, boron toxicity has been increased significantly. One of the applicable practices to rectify toxicity of boron is application of some nutrients such as silicon to the plant growth medium. To investigate this phenomenon, an experiment with the following treatments was designed and conducted. Six levels of boron, i.e. 0, 5, 10, 20, 40 and 80 mg B per kg of soil from the H3BO3 source and four levels of silicon,  i.e. 0, 70, 140 and 280 mg Si per kg of soil from the Na2Si3O7 source,  in four replications on potted mango seedlings. Seven-month old seedlings were harvested and B, Si, N, P, K, Na, Ca and Mg were measured in the plants tissue. The results indicated that application of the highest level of B resulted in high concentration of boron with different ratios in different tissues. The average concentration of B measured for the leaves was 2.4 X and root 1.2 X compared to the stem tissue. With increasing levels of boron, nitrogen concentration in leaves and roots decreased by 11.8% and 4.2%, respectively, and in opposite direction, nitrogen increased in the stems by 6.9%. However, at high levels of boron, with increased application of silicon, phosphorus concentration of the leaves exhibited an upward trend. Concentration of potassium in mango leaves increased by increasing levels of boron and silicon, but it was the opposite in the stem and root where the trend was decreasing. Interaction effects between boron and silicon in lower levels of boron was found a decreasing effect in absorption of calcium, which changed the direction to increasing effect in higher levels of boron. The interaction was always a decreased effect on concentration of magnesium. In overall, excessive boron caused a negative effect on concentration of nitrogen, phosphorus, and magnesium, and a positive effect on concentration of potassium and calcium. However, silicon application failed to exhibit a generally impressive correction role to suggest for field    conditions.