Seaweed extract and biological fertilizer to stimulate the growth of Khaya senegalensis irrigated with agricultural drainage water in greenhouse conditions for a sustainable forest plantation industry in Northern Egypt

Abstract

Due to the global deficiency in water, alternate water sources, such as agricultural drainage water (ADW), are now used to irrigate plants, particularly timber trees. A greenhouse experiment was carried out to assess the effects of irrigation schedules using ADW with or without Nile water (NW) on the growth of Khaya senegalensis seedlings. Additionally, the effects of mineral fertilizer (NPK) contains urea (46 % N), superphosphate (15.5 % P₂O₅), and potassium sulfate (50 % K₂O) at a dose of 1 g N, 0.5 g P₂O₅, 0.5 g K₂O/plant, seaweed extract (SE) at 7 mL/L from a commercial wild brown seaweed, Sargassum, and a biofertilizer Top Strains (TS)® at 30 mL/plant, as well as their combination on growth parameters of K. senegalensis seedlings were assessed. The plants that were irrigated with 100 % NW and fertilized with NPK + SE displayed the highest values in terms of shoot height (134.6 cm), leaf dry weight (123.28 g), stem dry weight (122.005 g), root dry weight (131.84 g), total dry weight (377.138 g), shoot/root ratio (1.858), shoot growth rate (4.53 cm/month), leaf area (447.176 cm²), leaf length (39.32 cm), number of leaves/plant (70.2), and number of leaflets/leaf (17). The plants irrigated with 100 % ADW and fertilized with NPK + SE had the highest chlorophyll content (57.159 SPAD units), followed by those irrigated with 50 % NW + 50 % ADW. The biomass production of K. senegalensis was moderately affected by the biofertilizer Top Strains (TS)®. The SE was subjected to chemical analysis using GC–MS, HPLC, and amino acid analyzers revealing the presence of several bioactive compounds. These included benzyl salicylate, oleic acid methyl ester, protocatechuic acid, pyrogallol, and benzoic acid, as well as the amino acids ammonia, alanine, glycine, and lysine, and the water-soluble vitamins thiamine and riboflavin. The biomass production from K. senegalensis was somewhat affected by adding SE, TS, or NPK fertilizers with irrigation regimes. Significantly, when K. senegalensis plants received irrigation with 100 % NW + 50 % ADW and treated with NPK + SE, most of their vegetative characteristics improved. The results have proved that fertilizer treatments and alternative water regimes are environmentally friendly and have economic applications to maximize the growth and yield of K. senegalensis.