Effects of foliar nitrogen fertilization on the phenolic, mineral, and amino acid composition of escarole (Cichorium endivia L. var. latifolium)

Nitrogen has a pivotal role in determining the quality of horticultural products, and foliar fertilization strategies could achieve higher nutrient use efficiencies while reducing environmental impacts and potentially enhancing consumer health benefits. Escarole (Cichorium endivia L. var. latifolium) plants were grown in nutrient solution, either complete or without N, and sprayed with different concentrations of foliar urea (0, 1, 5, and 10 g L−1). Total protein in the leaves was increased by the elevated concentrations of urea but the levels of total phenolics and total soluble sugars were lower. The contents of minerals in plants not receiving N in the nutrient solution were, in general, significantly increased by urea applications, but those of Cu and Zn were decreased. Additionally, the amino acids concentrations were boosted after urea application, whatever the composition of the irrigation solution, arginine, serine, and alanine being the most abundant amino acids. In conclusion, foliar N fertilization was an effective strategy to enhance the nutritional properties.