Performance of neem (Azedarachta inidica) seedlings with the addition of biostimulant treatments under wastewater irrigation conditions

A field experiment was conducted in the forested area affiliated with the wastewater irrigation plant located in Balana, Nasr El-Nuba District, Aswan Governorate, Egypt. This study was conducted from 15th September 2023 to 15th June 2025 to evaluate the impact of seaweed extract and humic acid as natural biostimulants on the growth performance of neem (Azadirachta indica) seedlings irrigated with treated wastewater. Homogenous seedlings of approximately 20-25 cm in height were planted in rows 5 m apart and 5 m within the row, with approximately 400 trees/ha. The experiment was followed the Completely Randomized Design (CRD), with three replicates. The experiment included five main treatments, control (without adding any soil amendments), humic acid at 1ml/l and 2ml/l and seaweed extract at 1g/l and 2g/l. The obtained results showed that applying seaweed extract or humic acid as biostimulants cleared significant differences in various growth characteristics of A. indica saplings. The highest average values of stem length, average branches number, stem diameter were recorded with the SWE at a rate of 2g/l, followed by HA at a rate of 2ml/l. Applying the SWE 2g/l treatment, followed by SWE 1g/l recorded the highest values of leaf area, leaf fresh weight, leaf volume, saturated leaf weight and leaf dry weight as well as the lowest values of leaf water content. Chlorophyll content was improved by biostimulant treatments, with the highest values were recorded with SWE 2g/l, followed by HA 2ml/l.