Effect of zinc and boron interaction on growth and mineral composition of lemon seedlings in a calcareous soil

The impact of different concentration of zinc (Zn) and boron (B) on growth and mineral composition of lemon seedlings (Citrus Aurantifolia L.) was studied under greenhouse conditions. We used five concentration levels of B (0, 2.5, 5, 10 and 20 μg g-1 soil) and three of Zn (0, 5 and 10 μg g-1 soil). Fresh and dry plant weights of the control treatment were strongly decreased with B levels higher than 5 μg g-1 of soil. In above mentioned B levels, lemon seedlings displayed slight to severe B toxicity symptoms. Zn treatments reduced B accumulation and the associated inhibitory effect on plant growth. Increased B level in soils enhanced the concentration of B in plant shoots to a greater extent in the absence of applied Zn. The effectiveness of Zn for the reduction of B accumulation and toxicity decreased as the level of applied B was increased. In a comparison of Zndeficient and Zn-treated soils, plant root and shoot analysis for B indicated an increased transport of B in the absence of Zn. The best plant production was achieved when 2.5 and 10 μg g-1 soil of B and Zn were applied simultaneously. This combination was associated with the highest uptake of Zn, nitrogen (N), phosphorous (P), potassium (K), iron (Fe), manganese (Mn) and copper (Cu), suggesting that the combination resulted to a suitable condition in which plants had a well-balanced nutritional status. While B application increased nutrients accumulation in plant shoot, the role of Zn was a dilution effect or antagonistic relationship. The results of this study indicated that supplemental Zn has potential and practical importance in the control of B absorption and toxicity in soil where plants are grown under Zn deficiency and B toxicity.