Abstract

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Current anaerobic digestion technologies are geared towards maximizing biogas yield and the subsequent use of the anaerobic slurries as soil amendments. However, only few studies have established the agronomic risk associated with the utilisation of anaerobic slurries. Therefore, this study evaluates the effect of agronomic use of anaerobic slurry on lycopersicum esculentum seedlings. L. esculentum is one of the most important vegetables worldwide. In this study, Palm esculentum Oil Mill Effluent (POME) collected from the Nigeria Institute for Oil Palm Research (NIFOR) was anaerobically digested at 1:1 effluent (E) to inoculum (I) ratio using the mesophilic technique. The physicochemical of the POME such as pH, Chemical Oxygen Demand (COD), lead, chromium, zinc, calcium, magnesium, phosphate, etc., were determined before and after anaerobic digestion. The anaerobic slurry was evaluated for their bio-fertility potential by using them as soil amendments at different doses: 0, 200, 400 and 600 ml/3 kg soil in a completely randomized design in triplicate followed by screenhouse trial. The physicochemical properties of the soil were determined using standard methods before and after the screenhouse experiment. The results showed that anaerobic digestion of the effluent was a successful biological treatment system with high COD removal efficiency (over 60 % reductions), while water properties such as total solids, nitrate, phosphate etc., were not considerably affected by the treatments. Result from the pre-plant soils revealed that the soil organic carbon, nitrogen, phosphorus, magnesium and calcium increased with increasing anaerobic slurry applications while the soil pH remained in the acidic region and the soil exchangeable acidity reduced. The plant height, number of leaves, leaf length, stem girth and total biomass yield by the plant significantly (p<0.05) increased with increasing anaerobic slurry treatments. Soil amendments with the anaerobic slurry improved soil fertility, plant nutrient and heavy metals uptake increased. Therefore, this should be applied with caution to avoid bio-accumulation of heavy metals in plants. Among the selected heavy metals evaluated, zinc in the 200 ml treatment had the highest uptake (195.50 mg/kg) while cadmium in the control and 200 ml treatment had the lowest (0.00 mg/kg).

Keywords: Anaerobic slurry, soil properties, tomato growth, heavy metals