Interaction of nitrogen and shading on tomato yield and quality

Although the use of shade cloths is an economic and common practice to mitigate the effect of high temperatures in greenhouse crops in warm areas, the decrease of solar radiation may alter some physiological processes of the plant, modifying their nutritional needs and ultimately affecting production and quality. In this paper we study the effect of nitrogen dose and its interaction with the use of shade cloths on the quality of tomatoes, with particular attention paid to their bioactive compound content. The treatments consisted of three levels of N (14, 7 and 3 mM), combined with two levels of light intensity, control (100% light), and shading (60% light) provided by shade cloth. Shading adversely affected the production of tomatoes cultivated with 14 mM N, although a lower dose of N offset the negative effect of shade on performance. Shading did not affect the concentration of sugars in the fruit, but decreased the phenolic compound and vitamin C contents. By contrast, a decrease in the dose of N increased the concentration of phenolic compounds at 100% light and that of vitamin C with and without shading. Shading decreased the concentration of beta-carotene only in the case of plants grown with the highest concentration of N. The concentration of lycopene, contrary to that observed for all other metabolites of interest, increased with shading. Under these shading conditions, the decrease in the dose of N did not affect the beta-carotene and lycopene concentrations.