Evaluation of acidifying nitrogen fertilizers in avocado trees with iron deficiency symptoms

The control of iron chlorosis by synthetic Fe chelates is costly, and their application can have adverse environmental impacts. We investigated the effectiveness of alternative strategies to prevent Fe chlorosis in avocado based on different acidifying nitrogen fertilizers. The experiment was conducted on a commercial orchard of avocado cv. Hass cultivated in a calcareous soil. The application of (NH4)(2)SO4 was highly effective at reducing the soil pH and, when applied with a nitrification inhibitor, at increasing the leaf chlorophyll concentration in trees. Fertilization with urea was also effective at increasing leaf chlorophyll, but only when applied without a nitrification inhibitor. However, the acidifying effect of urea on the soil was significantly lower than (NH4)(2)SO4. The different N sources also modified the concentration of N-NO3-, N-NH4+ and total N within the leaves, but did not influence the length of the shoots or the leaf gaseous exchange. These results suggest that the fertilization strategy based on (NH4)(2)SO4 + DMPP or urea can be an effective and sustainable alternative to counteract Fe chlorosis symptoms in avocado trees. Our results provide evidence of the effectiveness of agronomic strategies, alternative to synthetic Fe chelates, for preventing Fe deficiency in avocado.Comision Nacional de Investigacion Cientifica y Tecnologica (CONICYT) of Chile 1113032