Effect of L-Tryptophan and L-Glutamic Acid on Carrot Yield and Its Quality

Abstract

Positively affecting crop quality and yields, amino acids used as plant stimulants play a special role in ensuring global food security. L-tryptophan (L-Try) and L-glutamic acid (L-Glu) are important biostimulants that increase the yield of field crops and vegetables. Carrot is one of the most important vegetables due to its production volume in the world (sixth most consumed vegetable) and its nutritional value. The response of different plant species to amino acid application varies. The literature mainly deals with the effects of ready-made products containing a mixture of several amino acids, with no exhaustive studies on the effects of individual amino acids on carrot quality and yield. This paper is based on a two-year field experiment (2019–2020), in which the effect of two amino acids, L-Trp (7.5 g·ha−1) and L-Glu (60.0 g·ha−1), on carrot (Daucus carota L.) was investigated. They were applied to the leaves (FA) or both to the soil and to the leaves (S + FA), separately, (L-Trp or L-Glu) or as a mixture (L-Trp + L-Glu). The control plot was treated with mineral fertilizers only. The research was conducted as a field experiment in a split-block design. The yield of carrot storage roots and their content of dry matter, protein, sugars, total soluble solids (TSS), and ascorbic acid were determined. The amino acids positively affected the yield of carrots compared to the control, but only the synergistic action of L-tryptophan and L-glutamic acid increased it significantly. On average, for both amino acids the S + FA application increased the protein content and the marketable yield of storage roots significantly more than in response to FA treatment. A significant increase in marketable yield compared to the control was found after the combined soil and foliar application (S + FA) of all amino acid combinations, but the L-Trp + L-Glu mixture worked best. The storage roots of carrots grown on the plot with L-Trp + L-Glu contained significantly more protein and TSS than those on the control plot. The content of TSS was also positively affected by L-Trp used on its own, while L-Glu increased the content of ascorbic acid. Amino acids applied to the leaves (FA) increased the content of total sugars in the carrot roots more than when applied both to the soil and to the leaves (S + FA). Of all treatment combinations, the synergistic action of L-Trp and L-Glu made it possible to obtain the highest yields of carrot storage roots, containing the most protein and total soluble solids.