Nitrogen and Sulfur Effects on Leaf Lettuce Quality1

Nitrogen* sulfur fertilizer combinations and growing season effects on sensory quality/acceptability and color of hydroponically grown greenhouse lettuce cultivar, “Grand Rapids”, were studied. Lettuce samples were evaluated using an attribute rating scale for appearance, color, texture, flavor, bitterness and overall acceptability; actual leaf color was measured with a chromameter. Initially, 20 N*S treatment combinations were tested. Then based on specific sensory responses, eight N*S treatment combinations were selected forjurther study in the Winter and in the Spring. Univariate ANOVA showed that in both studies significant (P<0.05) color and texture differences were found. Generally, plants receiving the highest treatment level (240 mg/L) of nitrogen were greener (sensory) and darker and duller (chromameter) than the other samples. Spring samples receiving 30 and 60 mg/L N were perceived as having firmer texture. Between seasons, it was found that lettuce grown in the Spring was perceived as being greener and having a softer texture than lettuce grown in the Winter. Principal component (factor) analysis revealed three factors accounting for between 79 to 81% of the variance in the data. Factor loadings varied depending on the season grown.