BIOCHAR AND WASTEWATER USE IN URBAN AGRICULTURE: SOIL HEALTH AND PATHOGENIC PROPERTIES

Abstract

The ability of biochar and its potentials as a powerful soil enhancer that holds carbon and makes soils more fertile is well known. Likewise, the use of wastewater in agriculture has received the world‟s greatest attention due to the global water crisis. Wastewater is nutrientrich and its organic matter content serves as a soil conditioner and humus replenisher. This study therefore investigated the effect of biochar and wastewater in improving soil health and fertility. Not compromising on health risk of farmers and consumers, the pathogenic properties of the soil and vegetables under cultivation were assessed. The study was conducted in 2 ˟ 4 factorial experimental laid outs in Randomized Complete Block Design with four (4) blocks and 4 replications. The treatment included application of biochar at 20 tha-1, NPK at 212.5 kgha-1, Biochar at 20 Tha-1 + NPK at 212.5 kgha-1 and a control. Each irrigated with either wastewater or domestic piped water. Amaranthus spp. was used as a test vegetable crop in two cropping seasons (dry and wet). Standard laboratory analyses procedures were adopted for the microbial, chemical and enzymatic analysis. The study revealed significantly higher concentration of Fe and Al amongst the other elements analysed and these ranged 70044 – 86100 mg/l and 22064-26519 mg/l respectively. However, all other heavy metals analysed were lower than the WHO recommended standards. Wastewater application increased the absolute values of the macro-nutrients concentration with only phosphorus, carbon and nitrogen being significantly (P < 0.01) different. Amongst all the substrates used to induce the soil, citric acid had higher microbial respiration rate followed by glucose, alanine and basal respectively. All enzymes assayed in the soil were significantly different (P < 0.01) with wastewater plots recording the highest values. Feacal coliform and E. coli counts on soil and vegetables in both seasons exceeded the WHO limits. Salmonella spp. was negative on all vegetables in the two seasons except NPK and Biochar+NPK plots irrigated with wastewater in the dry season. Helminths eggs population was to be detected high in wastewater irrigated plots than piped water. However, no helminths egg was detected on the vegetables in the wet seasons regardless of the type of irrigation water. Identified helminth eggs were Ascaris lumbricoides, Strongyloides spp., Trichuris trichura, Schistosoma mansoni of which the major population was Ascaris lumbricoides. The study concluded that wastewater and biochar improves the physical, chemical and biological qualities of soil and should be encouraged. Yet, there is the need to reduce the potential health risks from the wastewater through further research.