Exogenous Azotobacter vinelandii application as a component of integrated plant nutrient management in 'Hass' avocado crops

Key message

Application of Azotobacter vinelandii is a strategy for 'Hass' avocado at various phenological stages, showing a 25% decrease in chemical fertilizer use while improving growth and physiological performance.

Abstract

Azotobacter-based bio-stimulants increase soil nutrient availability, provide substances for plant growth, and reduce fertilizer needs. We examined drench Azotobacter vinelandii (Av) application with two chemical fertilization levels (CF: 100% and CF 75%: 75% chemical soil fertilization) on physiological, nutritional, and fruit yield parameters. Over 20 weeks, three experiments were conducted on different avocado development stages: seedlings, post-transplantation, and mature trees. In each trial, plants received soil treatments with three commercial Av doses [2.5 (Av1), 5 (Av2), and 7.5 (Av3) mL L⁻¹], with two fertilization levels. Soil Av and CF treatments were applied every 30 days from treatment start up to 16 weeks after treatment initiation (WAT). In the seedling trial, treatments with CF 75% combined with either Av2 or Av3 result in improved seedling quality, as indicated by the Dickson Quality Index (DQI), which measures 0.58 for CF 75% alone and approximately 0.79 for CF 75% with Av2 or Av3 at 20 WAT. In post-transplantation trees, CF 75% + Av2 or Av3 improved relative growth rate (0.021 and 0.024 cm cm⁻¹ week⁻¹ for CF 75% + Av2 and Av3, respectively) compared to CF 75% plants (0.013 cm cm⁻¹ week⁻¹) at 20 WAT. Mature trees showed CF 75% + Av2 or Av3 treatments had higher agronomic efficiency (44.7 and 38.2% CF 75% + Av2 and Av3, respectively) than CF 75% trees at 20 WAT. Av could serve as an alternative strategy for integrated plant nutrient management in sustainable 'Hass' avocado production as it reduces chemical fertilization needs by 25% without impacting crop physiology.