Isatis tinctoria L.: biomass production and indigo dye yield as influenced by mineral or organic nitrogen fertilization.

Isatis tinctoria L., commonly referred to as woad, is an indigo-bearing plant. Although an extensive body of knowledge about its cultivation in different European countries is available, no comparative data on the role played by different nitrogen sources have yet been gathered. This research study was aimed at evaluating the response of woad to mineral or organic nitrogen fertilization in terms of biomass production and indigo dye yield. Field trials were conducted at a cooperative farm in Central Italy, where woad is regularly cultivated. On the basis of the overall data collected, it was concluded that woad biomass production is positively influenced by nitrogen fertilization, although it does not seem to be affected by the nitrogen source (mineral or organic). Furthermore, a positive correlation was found between fresh biomass and woad powder yield whilst the indigo dye concentration in fully expanded leaves was not affected by nitrogen fertilization.