Reduced N Fertilizer Application with Optimal Blend of Controlled-Release Urea and Urea Improves Tomato Yield and Quality in Greenhouse Production System

At present, excessive nitrogen (N) fertilizer application for tomato has attracted much research attention because of reducing fruit yield and quality and increasing fertilizer input cost and environmental pollution risks. A better management strategy of controlled-release urea (CRU) combined with normal urea for reducing the N application rate and maximizing tomato yield has led to the feasibility of their adoption in many cropping systems. The interactive effects of three blending ratios of urea to controlled-release urea (CRU) (6:4, 3:7, 0:10) and three levels of N fertilizer application rate (reduction by 15%, 30%, and 45% compared with conventional fertilization rate) on tomato yield and quality, economic return, nitrogen use efficiency (NUE), and soil inorganic N contents were investigated in greenhouse production system. The results indicated that application of CRU significantly increased tomato yield and NUE by 1.7–20.1% and 7.7–26.5%, respectively, compared with that of conventional fertilization (CF) treatment. Meanwhile, proper proportion of CRU and urea significantly improved tomato fruit Vitamin C concentration and sugar-acid ratio, which were 12.6–22.4% and 12.4–22.6% higher than that in the other N fertilizer treatments, respectively. The highest tomato yield and quality were achieved with the 15% reduction in N fertilization rate with urea to CRU blending ratio of 3:7, suggesting that the conventional N application rate exceeded what tomato requires. The study identified that a 15% reduction in N fertilization rate with urea to CRU blending ratio of 3:7 rendered a sustained supply of inorganic N in topsoil and optimal NUE during the growing season. This finding had practical implications for developing a sustainable N fertilization strategy, which reduced N fertilizer application with optimal blending of CRU with urea while maintaining high yield and quality for large-scale application in tomato production under greenhouse system.