Nitrogen (N) and boron (B) are mobile elements in soil. Therefore, the application of these nutrients is typically performed annually, as a single dose, or even splitting it into several fractions in the case of N. In olive (Olea europaea L.), however, controversial literature has suggested that yearly application of N may not be required. In the case of B some authors indicated that one single application is sufficient for three or four years. Thus, the effect of these elements on olive yield, leaf N and B concentrations, as well as soil available N and B were investigated during a field trial performed in an olive orchard located in NE Portugal, in which N and B were not applied for four consecutive growing seasons. Fertilizer treatments consisted of the following: the control, which was a ‘complete’ fertilization plan where N and B were included (N+B treatment); –N treatment, with N excluded from the fertilization plan; and –B treatment, with B excluded. Available soil N and B were estimated from a pot experiment with Italian ryegrass (Lolium multiflorum L.) and from chemical laboratory extractions. Olive yield decreased significantly in the –N treatment in comparison to the control. A slight yield reduction in the –B treatment in comparison to the control was also observed. Leaf N and B concentrations decreased significantly in the –N and –B treatments, respectively, in comparison to the N+B treatment. Soil available N and B at the end of the experiment were significantly lower in the –N and –B treatments, respectively, in comparison to the N+B control. The results showed a continuous decrease in olive yield and leaf N and B concentrations, which reflected the reduction in soil available N and B in the treatments lacking the respective nutrient. Therefore, it seems prudent the recommendation of adjusted rates of N and B every year to prevent reduction in tree crop performance and improve nutrient use efficiency.
