Photosynthetic efficiency of hydroponically-grown tomato plants to decentralized wastewater treatment systems (DEWATS) effluents and nitrified urine concentrate (NUC) as nutrient sources

Abstract

There is increasing interest and wide recognition of the potential use of human-excreta derived materials (HEDM) as fertiliser to supply essential nutrients needed for crop production. This has additional benefits as part of a reuse-oriented sustainable sanitation approach in efforts aimed at addressing sanitation challenges in many parts of the developing world. However, most work on HEDMs has focused on yield responses when compared to chemical commercial fertiliser sources using soils. Not much work has considered different systems such as hydroponic production. The physiological responses of plants to different HEDM when used in a hydroponic system is currently not well understood. This study evaluated the effect of decentralized wastewater treatment system (DEWATS) effluents and nitrified urine concentrate (NUC) as nutrient sources on hydroponically grown tomatoes. The study was conducted using 'Monica' determinate tomatoes planted in a polyethylene tunnel located at Newlands-Mashu Research Station, KwaZulu-Natal, South Africa. The experiment was laid out using a complete randomized block design and comprised of three treatments, namely, DEWATS effluent, NUC and commercial hydroponic fertilizer mix (CHFM). Each treatment was replicated three times giving nine experimental units of five plants each planted in a 5 L polyethylene pot. Data was collected on the following physiological variables: leaf area index (LAI), chlorophyll content index (CCI), stomatal conductance (gs), net CO(2) assimilation rate (A), intercellular CO(2) concentration (Ci) and the ratio of intercellular CO(2) and atmospheric CO(2) (Ci/Ca) were evaluated at vegetative stage, three weeks after transplanting. Results showed that tomato plants receiving CHFM had the highest LAI (3.00), followed by NUC (1.85) and DEWATS (1.48). CCI was significantly higher in the NUC treatments (42.58) compared to the CHFM (30.51) and DEWATS effluent (23.60). DEWATS effluent reported high values of A (22.75) followed by CHFM (22.40) and NUC by (14.56). The value of gs was higher in the DEWATS effluent (0.44) compared to the values of 0.110 and 0.021 observed for NUC and CHFM, respectively. Further, Ci was higher using DEWATS effluent compared to NUC and CHFM. The current study demonstrated that the use of HEDM such as NUC and DEWATS effluent as nutrient sources have comparable effects with commercial fertilizer mix with respect to the physiology of hydroponically grown tomatoes.