Evaluating the feasibility of human excreta-derived material for the production of hydroponically grown tomato plants - Part II: Growth and yield

Disposal of human excreta derived materials (HEDM), particularly domestic wastewater, presents a challenge in areas served with on-site sanitation systems, most particular in informal settlements. The use of HEDM for agricultural food production represents a couple of opportunities such as improved sanitation, household food security as well as the generation of informal income. In this study, tomato seedlings ‘Monica’ cv were grown in a hydroponic system and irrigated with HEDM (effluents from decentralized wastewater treatment system and nitrified urine concentrate). A commercial hydroponic fertilizer mixture was used concurrently as a control treatment. All the treatments were applied to the plants through fertigation using a drip irrigation system. Plant growth (plant height, stem diameter, leaf area index, root:shoot ratio and plant dry matter), physiological (photosynthesis and chlorophyll), yield components (fruit number, fruit mass, harvest index and crop yield), leaf nutrient composition (N, P, K, Mg, Ca, Cu, Mn, Fe, Zn and Na) and microbiological (Aerobic count, coliforms and faecal coliforms) parameters were measured to assess the potential of these HEDMs as nutrient sources for hydroponically produced tomatoes. The results showed that irrigating the tomatoes with HEDM increased harvest index relative to crops irrigated with a commercial hydroponic fertilizer mix. Tomato plants irrigated with a commercial hydroponic fertilizer mix achieved the highest growth and yield, however, irrigation with human excreta based sources improved plant physiological performance and leaf nutrient composition compared to crops irrigated with commercial fertilizer mix. In terms of microbiological analysis, tomatoes harvested from plants treated with HEDM recorded the highest population of bacterial count as compared to the commercial hydroponic fertilizer mix.These results showed that nutrients derived from human excreta can be a good source of nutrients for hydroponically grown tomatoes. Moreover this practice can effectively address the challenges of human waste disposal while at the same time providing the much-needed resources for increased food production through urban agriculture. However, further research on the effect of heavy metals, pathogens on tomato fruit quality is still needed for the adaptation of wastewater as nutrients sources for hydroponically grown tomatoes.