Iron sources for citrus rootstock development grown on pine bark/vermiculite mixed substrate

For high technology seedling production systems, nutrition plays an important role, mainly the fertigation with iron chelates to prevent its deficiency. This study had the goal of searching for alternative iron sources with the same nutrient efficiency but lower cost in relation to nutrient solution total cost. An experiment was carried out in 56 cm³-conic-containers tilled with a pine bark/ vermiculite mixed substrate using Fe-DTPA, Fe-EDDHA, Fe-EDDHMA, Fe-EDTA, Fe-HEDTA, FeCl3, FeSO4, FeSO4+citric acid plus a control, and the rootstocks Swingle, Rangpur, Trifoliata and Cleopatra, in a randomized complete block design, with four replicates. Seedlings were evaluated for height, relative chlorophyll index, total and soluble iron leaf concentrations. Cleopatra was the only rootstock observed without visual iron chlorosis symptoms. There was a low relative chlorophyll index for Rangpur, Swingle and Trifoliata rootstocks in the control plots, in agreement with the observed symptoms. High total iron concentrations were found in the control and Fe-EDTA plots, whereas soluble iron represented only a low percent of the total iron. The economical analysis showed the following cost values of iron sources in relation to the nutrient solution total costs: Fe-HEDTA (37.25%) > FeCl3 (4.61%) > Fe-EDDHMA (4.53%) > Fe-EDDHA (3.35%) > Fe-DTPA (2.91%) > Fe-EDTA (1.08%) > FeSO4+citric acid (0.78%) > FeSO4 (0.25%). However, only plants from Fe-EDDHA and Fe-EDDHMA treatments did not present any deficiency visual symptoms. The relative cost of Fe-EDDHA application is low, its efficiency in maintaining iron available in solution resulted in high plant heights, making it recommendable for citric rootstock production in nurseries