Reduction in Nitrogen Prior to Harvest Increases Phenolic Content of Baby Red Lettuce Leaves

Abstract

This study investigated baby red lettuce leaves grown in an inert media and fertigated with 300 or 1000 mg · L -1 CaNO 3 -N (19% Ca; 15.5% N), and the effects of altering CaNO 3 -N concentrations in the last 7 days prior to harvest on yield, antioxidant capacity, TPP and vitamin C content. Plants receiving 1000 mg · L -1 CaNO 3 -N had a significantly higher leaf FW than those fertilized with 300 mg · L -1 CaNO 3 -N after both 21 and 28 days. Pulsing plants with 1000 mg · L -1 CaNO 3 -N for 7 days after 21 days at 300 mg · L -1 CaNO 3 -N resulted in a significant increase in FW of 14%, compared with plants receiving 300 mg · L -1 CaNO 3 -N. After 28 days plants fertilized with nitrogen at 300 mg · L -1 CaNO 3 -N were significantly higher in TPP than those fertilized with 1000 mg · L -1 CaNO 3 -N. While there was no significant effect on TPP of a 7-day 1000 mg · L -1 CaNO 3 -N pulse added to 300 mg · L -1 CaNO 3 -N, a 7-day pulse of 300 mg · L -1 CaNO 3 -N added to 1000 mg · L -1 CaNO 3 -N resulted in a significant increase in TPP. These results indicate that reducing the N availability for 7 days prior to harvest can result in a significant increase in plant phenolic content with no adverse effect on yield.