Response of Tomato Crops (Solanum lycopersicum 'Montecarlo') to Sewage Sludge-Based Compost Fertilization

The agricultural use of anaerobically digested sewage sludge (ADSS) as an organic amendment to improve soil fertility is gaining importance. However, the management of this raw organic waste is not exempt of several problems. To overcome this, ADSS is usually co-composted with different bulking agents, thus obtaining a humus-like material, easy to store, with improved nutrient content but also with some amounts of heavy metals and salts, which may be toxic at some concentrations. This study aims to determine the effectiveness of a sewage sludge-based compost as a soil organic amendment for growing tomato plants (Solanum lycopersicum 'Montecarlo'). Once obtained the mature compost and having verified its physico-chemical and biological characteristics, it was used in different substrates containing the compost and/or traditional fertilizer under greenhouse conditions. The effect of the different substrates was determined at three stages of plant development (flowering, fruiting, and ripening), as was their nutritional state, boron and heavy metal contents. Growing of tomato plants was similar in the treatment in which part of the synthetic fertilization had been substituted with composted sludge when compared with plants grown with traditional fertilization. The addition of the sludge-based compost produced no harmful effects in terms of the accumulation of boron or heavy metals in fruit. The obtained results suggest that the partial substitution of chemical fertilization by an organic amendment in the 'Montecarlo' tomato cultivar did not diminish the development of these plants and toxic elements did not accumulate. These results are particularly relevant in economic and environmental terms.