Construction of comprehensive nutritional quality index for tomato and its response to water and fertilizer supply.

In recent years, the nutritional quality of vegetables has been increasingly concerned by people and investigated by researchers. However, the decline in vegetable internal quality is common due to excessive irrigation and irrational fertilization. Although tomatoes have been grown successfully for many years, there is no accurate formula or recipe on amount of irrigation or fertilizer levels to get tomato fruit with high quality. For tomato fruits, the nutritional quality largely depends on the content of soluble solids, soluble sugar, titratible acid, Vitamine C and lycopene, some of which are correlated with each other. Therefore, tomato nutritional quality could not be assessed according to any one of these attributes. But the comprehensive evaluation of vegetable nutritional quality has not been well studied yet. To construct a comprehensive nutritional quality index of tomato fruits and investigate its response to irrigation amount and fertilizer rates of nitrogen, phosphorus and potassium, a composite quadratic orthogonal regressive rotation design of four factors and five levels was used in a pot experiment. The contents of soluble solids, soluble sugar, titratable acid, lycopene, Vitamin C and sugar-acid ratio were determined for tomato fruits. By using entropy weighting method, the objective weights of six single quality attributes were calculated based on measurements of these attributes. The subjective weights of these six attributes were calculated based on the analytic hierarchy process (AHP) from survey data from both consumers and horticulture experts. Based on these, the comprehensive weighting method of game theory was used to determine the balanced weight of single tomato quality attributes. Results indicated that the attributes were ranked based on their importance by lycopene>sugar-acid ratio>Vitamin C>soluble sugar>soluble solid>titratable acid. The comprehensive nutritional quality index was constructed according to the technique for order preference by similarity to ideal solution (TOPSIS). Moreover, a regression model on the amount of irrigation water and fertilizers and tomato comprehensive nutritional quality index was established. Based on the regression equation, the single, interactive and coupling effects of these four experimental factors on the comprehensive nutritional quality index were analyzed. The results showed that the main effects of four experimental factors on the comprehensive nutritional quality were ordered by P rate>N rate>irrigation amount>K rate. If codes of other three factors were zero, the comprehensive nutritional quality showed a downward quadratic parabola in response to the increase of irrigation amount, as it did in the case of N rate. It is interesting that an upward quadratic parabola occurred with the increase of K rate. The comprehensive nutritional quality increased linearly with P rate. Interaction between amount of irrigation and N, P and K fertilizers significantly affected comprehensive quality of tomato fruits. It indicated that comprehensive tomato nutritional quality decreased with excess input of irrigation amount and N fertilizer, and could be improved by appropriate supply of P and K fertilizers. The findings from this study also allowed us to optimize comprehensive evaluation of vegetable quality that could be used to study the management of water and fertilizers in the future. [ABSTRACT FROM AUTHOR]