Identification of optimal irrigation and fertilizer rates to balance yield, water and fertilizer productivity, and fruit quality in greenhouse tomatoes using TOPSIS

The precise management of water and fertilizer is necessary to maximize greenhouse tomato production. Irrigation quantity and fertilizer application rate were experimentally varied to determine their effects on tomato yield, water and fertilizer productivity, and nutritional and flavor quality over four consecutive growing seasons in two cities, Yangling and Baoji. The experiment was designed as a quadratic orthogonal rotation combination with two factors at five levels and a total of 16 treatments. TOPSIS (technique for order preference by similarity to an ideal solution) models were created to predict the effects of drip irrigation water quantity and fertilizer application rate on indicators of tomato water and fertilizer productivity, yield and quality. The tomato indicators showed a downward opening quadratic relationship with irrigation quantity and a similar relationship with fertilizer application rate. The composite indicators exhibited a downward opening paraboloid relationship with irrigation and fertilizer rates. Tomato pan coefficient (Kcp) values in the range 0.74–0.78 and the fertilization coefficient (Kf) values in the range 1.13–1.27 produced optimal tomato growth in all experimental plots. To ensure the results of this study are of practical use, over 95% of the highest composite indicators were used to identify the optimal range of Kcp as 0.68–0.83 and the optimal range of Kf as 0.98–1.34 in spring, with corresponding ranges in fall being 0.68–0.82 and 1.06–1.41. This study proposes a method for analyzing tomato growth and provides guidance for precise irrigation and fertilizer management in greenhouse tomato production in Northwest China.