NITROGEN SOURCE AFFECTS CRUNCHINESS, BUT NOT LETTUCE YIELD

Abstract

While nitrogen (N) form affects growth and yield of many vegetables crops, previous studies suggested that N-form may affect lettuce (Lactuca sativa L.) quality more than growth and yield. The objectives of this research were to evaluate the effect of the N-source used as injection material on the field performance and sensory attributes of three lettuce types. Three lettuce types (Romaine, butterhead and looseleaf) where grown with plasticulture and sidedressed with weekly injections of calcium nitrate, potassium nitrate, or ammonium nitrate, each at a rate of 7 kg N ha⁻¹ week⁻¹. All lettuce type reached marketable size 49 days after transplanting. N-source effect on marketable yield and head number was not significant (P>0.05). After harvest, lettuce samples were prepared for sensory evaluation. In a quiet session, panelists (n=36) were instructed to rate each sample for bitterness, sweetness, crunchiness, and overall preference on a 9-cm Hedonic scale. Sensory ratings were similar for all three lettuce types. Panelist found that crunchiness of calcium nitrate-fed plants (4.8 cm) was significantly (P=0.05) higher than that of plants receiving potassium nitrate (4.4 cm) or ammonium nitrate (4.2 cm). These results suggest that while growers may use ammonium nitrate because of its cost, they should consider using calcium nitrate to enhance lettuce crunchiness.

Keywords:

• Calcium nitrate
• Potassium nitrate
• Ammonium nitrate
• Romaine
• Cos
• Looseleaf
• Butterhead
• Lactuca sativa.

ACKNOWLEDGMENTS

We thank Stokes Seeds and Vilmorin for supplying lettuce seeds, and Lewis Taylor Farm, Inc., Tifton, GA. for producing lettuce transplants. Appreciation is extended to Karen Dane, Research Assistant, for her help during the taste test.