THE IMPACT OF DIFFERENT AMMONIUM:NITRATE RATIOS AND SALICYLIC ACID ON GROWTH AND BOLTING TIME OF LETTUCE GROWN UNDER HYDROPONIC CONDITIONS

Abstract

A good ammonium:nitrate ratio may help lettuce grow faster, produce more, and be of higher quality by making it easier for the plant to absorb, use, and make food from nitrogen. Delayed bolting is a desired characteristic for lettuce cultivation, and exploiting different options to achieve delayed bolting could help to harvest a better yield and extend crop duration. Salicylic acid (SA) could help to improve lettuce growth and regulate bolting. Although some individual studies have been conducted to infer the role of varying ratios of ammonium:nitrate and SA doses on the growth and development of lettuce, the influence of their interactive effect on lettuce growth and bolting remains elusive. The purpose of this study was to find out how different amounts of ammonium:nitrate and SA affected the growth and bolting time of lettuce grown under hydroponic conditions. Three different ammonium:nitrate ratios (100% NO3 :0% NH4 , 80% NO3 :20% NH4 , and 40% NO3 :60% NH4 ) and four SA doses (0, 0.75, 1.5, and 3.0 mM) were included in the study. Lettuce seedlings were transplanted into the soilless system on March 13, 2024. The SA was applied to plant leaves when they had 5–6 leaves (14 days after transplanting, i.e., 27 March). Half of the plants in the study were harvested at harvest time, while the remaining were allowed to bolt until bolting. Data relating to head weight, diameter, biomass, stem length, diameter and biomass, root length and biomass, total soluble solid matter, chlorophyll index, vitamin C, and time to bolting were collected. All measured traits (except total soluble solid matter) were significantly altered by the individual and interactions between SA doses and ammonium:nitrate ratios. The interactive effect of ammonium:nitrate ratios and SA doses caused a little delay in bolting. The highest nitrate ratio (100% NO3 :0% NH4 ) delayed bolting by 5-6 days. The onset of the heatwave during the late season probably induced bolting. Therefore, the experiment should be conducted in a controlled greenhouse to better understand the impact of SA. Furthermore, biochemical changes in lettuce should be investigated in future studies.