Liquid organic fertilizer production for growing vegetables under hydroponic condition

PURPOSE: Liquid organic fertilizers produced from agricultural residues and industrial wastes are becoming increasingly popular. This study aimed to examine the effect of liquid organic fertilizers produced from waste molasses, distillery slop and sugarcane leaves on the growth of Green Cos Lettuce (Lactuca sativa var. longifolia). METHODS: Six formulas of liquid organic fertilizers were produced with different ratios of substrates (molasses, distillery slop and sugarcane leaves). The measurements of chemical, microbiological and germination index of fertilizers were studied. Hydroponic using nutrient film technique system was used to grow vegetables with fertilizers. RESULTS: Fertilizers showed the ranges of chemical parameters as follows: pH 4.5–7.8, EC 25–33 dS/m, total N 0.14–0.33%, total P₂O₅ 0.002–0.017%, total K₂O 0.81–11.8%, OM 0.26–3.25%, OC 0.26–3.20% and C:N ratio 6.14–17.92. Microbiological analysis indicated total microorganism of 9.99–9.05 logCFU/ml. Nitrogen fixers, phosphate and potassium solubilizing agents were found in all formulas. IAA concentration was 1.13–59.53 mg/l. The fertilizers produced after 30 days of fermentation and used at a dilution of 1:100 gave more than 100% germination index showing non-phytotoxicity characteristics. The results for the hydroponic system showed that liquid fertilizer formula 3 (distillery slop: sugarcane leaves: filtrate water 1:0.1:0.25 v:w:v) and formula 5 (distillery slop: sugarcane leaves 1:0.25:0.25 v:w:v) demonstrated the best growth performance, which was similar to plants treated with liquid chemical fertilizer. CONCLUSION: This study showed that organic liquid fertilizers formulas 3 and 5 had similar growth promotion properties as chemical fertilizers with Green Cos Lettuce. Moreover, our products are organic and serve as a rich nutrient source for the plant.