The effects of nitrification inhibition and phosphonate on 'Hass' avocado yield and Botryosphaeria susceptibility

L. Winer
Phosphonate is globally used in avocado production for the control of root rot caused by Phytophthora cinnamomi. The phosphonate mechanism of action is to increase the plant’s resistance to different groups of fungi. Recently it was reported to be effective in avocado against Botryosphaeria as well. The present research was performed in Israel on a ‘Hass’ avocado orchard planted in clay soil of high pH, that displayed no symptoms of Botryosphaeria. Use of a nitrification inhibitor, phosphonate or a combined treatment with the two components were compared with a control treatment. All four treatments were administered together with fertilizers through the irrigation system at constant concentrations during the entire irrigation season. The fertilizer components were uniform in all four treatments, using ammonium as the main source of nitrogen. Inhibition of the nitrification process increased the soil concentrations of nitrogen approximately 3-fold, mostly by increasing the ammonium component. The water soluble phosphorous in soil solution was increased by 3.7- to 5.5-folds in treatments that included K-phosphonate. The availability of potassium as represented by its concentration in the saturated paste of the soil increased from 14.0 to 22.6 mg kg‑1. Phosphonate or nitrification inhibitor caused an increase in the mean yield of three consecutive seasons from 11.3 to 14.9 and 14.7 t ha‑1, respectively. Combined treatment of the nitrification inhibitor with phosphonate when the trees were fertilized with ammonium resulted in a significant mean yield increase to 16.4 t ha‑1 (about 45% above the control). Trees started developing branch dieback symptoms related to Botryosphaeria only during the third season of the trial. The combined treatment of phosphonate and nitrification inhibitor dramatically decreased the susceptibility of the trees to those symptoms. The administration of phosphonate alone was only slightly effective.
Winer, L. (2022). The effects of nitrification inhibition and phosphonate on 'Hass' avocado yield and Botryosphaeria susceptibility. Acta Hortic. 1333, 133-140
DOI: 10.17660/ActaHortic.2022.1333.18
ammonium-N, nitrate-N, Persea americana

Acta Horticulturae