Effect of ammonium/nitrate ratio on growth and development of avocado plants under hydroponic conditions

Abstract

An experiment was carried out to study the effects of the proportion of ammonium (NH4+) and nitrate (NO3-) in the nutrient solution on avocado plants in a hydroponic system. Five treatments were applied, consisting of the following proportions of ammonium to nitrate ions in the solution: T0 = 0:4, T1 = 1:3, T2 = 2:2, T3 = 3:1 and T4 = 4:0 at a constant nitrogen concentration of 4 mM. After 4 months, the plants were harvested and fresh and dry matter accumulation, leaf area, and leaf nitrogen and carbon content were measured. An architectural description of the shoot (length, number of nodes and branching) was made. Dry matter of shoots and leaves all decreased with increasing NH4+ concentrations. In contrast, water content in aerial organs increased with NH4+ concentration. Nitrogen and carbon content and the relationship between dry matter production and leaf nitrogen were not significantly affected by the treatments. The architectural analysis showed that the shoots developed over time in one or two distinct growth units. While nitrogen form affected bom growth units, the second one was more severely affected, showing decreased length, number of nodes, and branching when NH4+ concentration increased.