2018 ASHS Annual Conference

Olive (Olea europaea L.) is considered one of the most important agricultural crops worldwide with an olive oil production of about 2.8 million tons in 2016. The influence of nitrogen (N) levels and sources on olive growth have been commonly researched in established orchards, but is limited in young olive plants, especially on the effects of root dynamic and physiological traits. The objective of this two-years field study was to evaluate the effects of N levels and sources on root growth dynamics, leaf-level gas exchange [photosynthesis (Pn), transpiration (E), and stomatal conductance (gs)] and leaf nutrient content of young ‘Arbequina’ olives. Nitrogen treatments were, control (no N), nitrate (NO₃^-) form applied as calcium nitrate (CN) at 20, 40 and 60 kg ha^-1, and ammonium (NH₄⁺) applied as urea at 20, 40 and 60 kg ha^-1. Root analysis derived from minirhizotron images revealed that the application of N significantly reduced root length intensity (L_a, mm cm^-2) compared to control olives in both years. In addition, no significant difference was noticed between N forms for L_a in 2015. In fact, leaf N% in control olives was above the N deficiency thresholds; i.e. 2.1% in 2015 and 2.57% in 2016. In both years, control-untreated seedlings had higher plant height, stem diameter and branch number than olives that received 40 or 60 kg ha^-1-N. We attributed the high performance of control (no N) seedlings to adequate N level in the soil (NO₃^-~ 25 mg kg^-1) from previous year application and the extra N supply from irrigation water and rainfall. However, leaf mineral concentrations were inconsistent (P, Ca⁺², Na, Zn, Fe, Cu) or not significant (Mn, S and B). In addition, no significant difference was noticed between treatments in gas exchange (Pn, gs and E). Overall, N applied to reach the sufficiency leaf N threshold level (2%) in olive reduced L_a. In addition, N application may not be required if pre-plant soil NO₃ levels are normal (~ 25 mg kg^-1).