Biosolids From Wastewater Treatment Pond ss A Potting Substrate for Greenhouse Tomato (Solanum Lycopersicum L.) Production

Abstract

Farmers in developing countries are rapidly adopting greenhouse tomato (Solanum lycopersicum L.) production for high productivity and fruit quality. However, soil borne pests and pathogens, and nutrient depletion limit the productivity of soil grown tomato. Containerized tomato production using biosolids from treated sewage may alleviate the aforementioned problems. Four experiments were conducted at Egerton University to evaluate the potential of biosolids (BS) from the university sewage sludge as a potting substrate for greenhouse tomato production. The first experiment compared BS from Egerton University Wastewater Treatment Plant (WWTP) with forest soil (FS), coco peat (CP) and tea compost (TC) in a completely randomized design to determine its suitability for crop production in terms of physico-chemical and biological properties. The second experiment determined the effect of biosolids-forest soil mixing rates of 0%, 10% (1:10), 20% (1:5), 30% (3:10), 40% (2:5), 50% (1:2) and 60% (3:5) (v/v), on tomato seedling emergence and growth in a randomized complete block design (RCBD) with four replications. The third experiment determined the effect of biosolids-blended forest soil and NPK fertilizer on growth and fruit yield of greenhouse tomato in a split plot embedded in RCBD replicated four times. The rates of NPK fertilizer (0, 100 and 200 kg ha-1) and BS (0%, 10%, 20%, 30%, 40% (v/v)) were the main plot and subplot factors respectively. The fourth experiment evaluated the impact of BS treatment combinations used in experiment three on postharvest quality and safety of tomato. Harvested tomato fruits were subjected to laboratory analyses for postharvest quality and safety (heavy metal accumulation and biological contaminants). The results revealed that BS was comparable or superior to commercial substrates (CP and TC) in a number of physico-chemical and biological properties. Addition of BS to FS at the rate of 30% was not significantly different from TC in enhancing tomato seedling emergence and growth. Enhanced tomato growth and yield as well as superior postharvest quality and safety of fruits were consistently achieved by combining BS-blended FS at 10% with NPK at100 kg ha-1. However, this treatment combination was not different from BS-blended FS at 30% without NPK fertilizer for some growth and postharvest parameters. Biosolids-blended FS at 10% with application of NPK fertilizer at 100 kg ha-1 is recommended for potted greenhouse tomato. Where fertilizer is unavailable, BS-blended FS at 30% can be used as a potting substrate for transplants and greenhouse tomato production.