Vermicomposting of Camel (Camelus dromedarius) Manure with Fly Ash and Microbial Inoculants: Effects on Nutrients and Heavy Metals

Abstract

This study evaluated the effects of fly ash (F) and effective microorganisms (EM) on nutrient dynamics and heavy metal transformations during vermicomposting of camel manure (CM). Four treatments (CM, CM + F, CM + EM, and CM + F + EM) were arranged in a completely randomized design and monitored over 12 weeks. Significant (p < 0.05) treatment and time interactions were observed for pH, NH4-N, Mn, Pb, and Mo. The addition of EM resulted in a greater decline in pH compared to other treatments. After 12 weeks, Olsen P increased from 300.62 to 398.71 mg/kg in CM + EM, while NH4-N increased markedly from 22.74 to 86.62 mg/kg. In contrast, NO3/NO2-N declined in EM-amended treatments but increased in the control and CM + F. Trace metal concentrations generally increased due to mass reduction during vermicomposting yet remained within internationally acceptable limits. Germination index (GI) values varied significantly among crops and treatments, ranging from phytotoxic to non-phytotoxic responses. Although CM + EM produced superior nutrient enrichment, several vegetables exhibited GI values below 50%, indicating potential phytotoxicity for sensitive crops. In case of established crops for which nutrient supply outweighs early phytotoxic concerns, CM + EM represents the most agronomically beneficial option. Future studies should explore blending CM + EM and CM + F with stabilizing amendments such as biochar to optimize nutrient availability while minimizing salinity and phytotoxic risks.