Effect of Application of Sulfuric and Humic Acid in the Mitigation of Root Asphyxiation Stress in Potted Avocado Plants

Avocado crop is very sensitive to root asphyxiation. Among the agricultural management techniques, soil applications of humic and sulfuric acids became increasingly popular. In a trial with potted 'Hass' avocado trees grown on a silty-clay soil, different soil treatments were applied to determine their effects on tree physiology and soil characteristics: Control, deionized water; SA, H2SO4 application; HA, humic acid application; SA+HA, combination of both treatments. Treatments were applied during a 9-month period. SA reduced soil pH, rised electrical conductivity and reduced saturated soil hydraulic conductivity (Ks) in the upper layers of the potted soil. On the other hand, HA increased electrical conductivity and Ks compared with Control. None of the treatments improved CO2 assimilation, stomatal conductance, stem water potential, chlorophyll fluorescence, growth or nutrient content. Our findings suggest that a rapid and positive response to the application of acids is unlikely to be observed under conditions of restricted oxygen in the root zone.