Avocado fertilization: Matching the periodic demand for nutrients

The main objective of this study was to assess the seasonal nutrients requirement of 'Hass' avocado trees grown in lysimeters, especially during flowering and the early period of fruit development that may affect later on the fruitlet abscission and determine crop yield. The experimental design included three fertigation treatments applying a fixed nutrient solution at three different starting dates of fertigation: (a) T1 - continuous fertigation, including macro nutrients (N-P-K) and micronutrients application, all over the year; (b) T2 - no fertilization (only irrigation) until 15 March, and fertigation as T1 since then; (c) T3 - no fertilization (only irrigation) until 15 May, and fertigation as T1 since then. Absence of fertilization during the winter period induced leaf-chlorosis while healthy, dense and plenteously green leaves characterized the fertilized trees (T1). The beneficial effect of early fertigation on fruit yield was statistically significant, mostly because of higher fruit number. Leaf analyses are commonly used in the avocado industry as a guide for fertilization yet; fruits rather than leaves are the main products of avocado orchards. Consequently, fruit rather than leaf analyses should determine fertilization management. Based on fruit growth data and nutrient concentration in the fruit, the N, P and K quantities removed by 'Hass' avocado fruit yield of 30 t ha(-1) were 120, 25 and 240 kg ha(-1). Taking into account common efficiency consideration (nutrient quantities removed by fruit yield divided by quantities added), the annual quantities of N, P and K required for attaining high quality avocado yield are 250-300, 80-120 and 500-600 kg ha(-1), respectively. Thus, fertilization rate together with nutrient combination should be modified in order to insure optimal fruit development.