19 Bulgarian Journal of Agricultural Science, 26 (Suppl. 1) 2020, 19-29 Influence of different doses of mineral fertilizer and the controlled water deficit on the antioxidants parameters in tomatoes (Solanum lycopersicum L.) irrigated with a drip irrigation system Antoniya Stoyanova 1* , Petya Veleva 2 , Elica Valkova 3 and Mitko Georgiev 1 1 Trakia University, Faculty of Agriculture, Department of Plant Breeding, Stara Zagora 6000, Bulgaria 2 Trakia University, Faculty of Agriculture, Department of Agricultural Engineering, Stara Zagora 6000, Bulgaria 3 Trakia University, Faculty of Agriculture, Department of Microbiology, Biochemistry and Physics, Stara Zagora 6000, Bulgaria *Corresponding author email: toni_1219@abv.bg Abstract Stoyanova, A., Veleva, P., Valkova, E. & Georgiev, M. (2020) Influence of different doses of mineral fertilizer and the controlled water deficit on the antioxidants parameters in tomatoes (Solanum lycopersicum L.) irrigated with a drip irrigation system. Bulg. J. Agric. Sci., 26 (Suppl. 1), 19-29 The main objective of this study is to analyze the mutual influence of different irrigation schemes and fertilization rates on the greenhouse tomato yield, and the irrigation water usage efficiency for a period of three years (2016-2018). Different irrigation schemes have been examined, achieved by reducing the irrigation depth at different levels. Fertilization plays an important role in the technological process with different rates. This experiment was focused on the effect of both factors (the fertilization rate and the irrigation regim) on the main quality parameters of the greenhouse tomatoes. Multivariate data analysis was applied to process the data, including Scheffe and Dunnett’s tests (depending on the Levene's test of equality of variances) were used to find the significant differences (P < 0.05) between the control variant and all other irrigation and fertilization schemes based on the investigated quality parameters (Dry matter, %; Ascorbic acid, mg%; Titrable organic acids, %; General dyes, mg%; Lycopene, mg% and β - carotene, mg%) in greenhouse-grown tomatoes. The analysis showed a medium to a high correlation (R 2 = 0.988, 0.990, and 0.062 for the three investigated years) between Dry matter content and the two investigated factors (the fertilization rate and the irrigation depth) and a very strong correlation (R 2 = 0.999, and 1.000) between Ascorbic acids and both factors of influ- ence for the first two years and a weak correlation (R 2 = 0.287) for the third experimental year. A weak to moderate cor- relation between Titrable organic acids (R 2 = 0.414, 0.669, and 0.079), β – carotene (R 2 = 0.252, 0.673, and 0.471), and both influencing factors were found, and a moderate correlation between General dyes (R 2 = 0.532, 0.815, and 0.590), Lycopene (R 2 = 0.685, 0.796 and 0.643), and the variants of irrigation and fertilization for the three experimental years. Keywords: antioxidants; fertilization; greenhouse tomato; irrigation regime Abbreviations: FAO – Food and Agriculture Organisation in the United Nations, FC - Field capacity, GLM - General Linear Model, LFMC - Limited field moisture capacity, PRD - Partial root zone drying, RID - Regulated irrigation capacity, SD - Standard Deviation, TSS - Total soluble solid Introduction The cultivated tomato (Solanum lycopersicum L.) is the world’s most highly consumed vegetable due to its status as a basic ingredient in a large variety of raw, cooked, or processed foods. This culture has gained immense popularity, especially in recent years with the discovery of the antioxidant activities and anti-cancer functions of Lycopene (Wu et al., 2011; Raiola et al., 2014). Tomatoes are rich in protein, amino acids, mineral salts, but their antioxidant properties are especially important. Within their nutritional composition, tomatoes stand out as an important source of antioxidants, such as vitamin C and Lycopene, compounds that provide benefits to human health, protect against oxidative damage, reduce the risks associated with cancer and prevent cardiovascular disease (Story et al., 2010).