By-Product from Livestock Waste Recovery System Used as Fertilizer: Bioactive Compounds and Antioxidant Activity of Tomato Fruit as Affected by Fertilization under Field and Greenhouse Conditions

Abstract

Conversion of livestock manure into organic fertilizer is a sustainable strategy in crop production. In contrast to composted manure, the agronomic characteristics of an anaerobic digestion by-product, digestate, have not been well characterized. This study aimed to investigate the effects of digestate and compost, derived from a pilot-scale livestock waste recycling system, on bioactive compounds in tomato fruits. Both field and greenhouse experiments were conducted to compare the effects of these two organic fertilizers with the application of chemical fertilizer. These comparisons were made by evaluating their influence on tomato yield and bioactive compound contents and antioxidant activity of fruits. The experiment included a control (no fertilizer) and three fertilization treatments with the same nitrogen dose: chemical fertilizer, digestate, and compost. The results revealed that the application of digestate and compost yielded similar results in terms of tomato production, surpassing both the chemical fertilizer application and the control group under both field and greenhouse conditions. Fertilization exhibited a significant influence on the bioactive compound contents and antioxidant capacity of the fruits. Furthermore, the application of digestate and compost led to an increase in the concentration of sugars, phenolic compounds, and several organic acids in the fruits while simultaneously reducing the citric acid levels in comparison to the chemical fertilizer treatment. Moreover, the application of both organic fertilizers improved the total phenol and total flavonoid contents in tomato fruits, and the antioxidant capacity in fruits was significantly higher than that of the chemical fertilizer treatment. In conclusion, the application of digestate or compost derived from the livestock waste recycling system reduced use of chemical fertilizers and resulted in higher tomato yields and fruit with considerably superior bioactive compounds. The results suggested that using digestate or compost as an alternative to inorganic fertilizers for tomato cultivation could assist farmers in increasing productivity, improving the content of bioactive compounds in tomato fruit, and promoting agricultural waste management.