Effect of Organic Fertilizers on Avocado Trees (Cvs. Fuerte, Hass, Lamb Hass) in Western Crete, a Cool Subtropical Region

The market for avocado is one of the fastest expanding worldwide, inclduing the Mediterranean basin. Organic farming systems cannot make use of synthetic fertilizers and therefore rely on several cultural techniques to maintain vigorous young trees and for quick shoot development, satisfactory yield, and fruit quality. We studied the effect of three different organic products (Terra Insecta (R) (Aeiphoria-Sustainable products of Crete, Chania, Greece), Fruit-Fix (R), and AMINO-16 (R) (both products manufactured by EVYP, Sindos, Thessaloniki, Greece) on avocado plants in the cool subtropical area of southern Greece. Three experiments were carried out, two of them on young avocado trees, and the third one on mature, fully productive trees. The establishment success (ES) (%), plants with shoot induction (SI) (%), plants with shoot growth >= 3 cm (SG) (%), number of sprouted buds >= 3 cm per plant (SB), mean shoot length (cm) per plant (SL), total shoot length (cm) per plant (TSL), mean leaf number per plant (LN), and total leaf number per plant (TLN) were measured in the first and second experiments, while in the third experiment, fruit growth parameters (length, width, fruit weight, fruit weight increase (FWI)) and fruit quality parameters (dry matter, oil concentration, dry matter, and oil concentration increase) were measured. The application of 0.2 K of Terra Insecta (R) to the planting hole did not have any statistically significant effect on plant growth, but when added around the trunk, statistically higher values were observed for SB, SL, LN, TSL, and TLN in the Terra Insecta (R) treatment compared to the control. Fruit-Fix (R) application to Lamb Hass avocado trees resulted in significant differences in ES, SI, SG, SL, TSL, LN, and TLN, and in the Hass variety, in SB. In the AMINO-16 (R) experiment, the fruit dimensions, quality parameters, and yield of the Hass variety were not recorded as significantly different. However, in the Fuerte variety, FW increased by 119.3% in the AMINO-16 (R) treatment. The effect of the organic fertilizers used in this research showed noticeable results requiring studies to be carried out over more seasons, different tree ages, cultivation methods, and stress conditions.