Paper
Interactive Effects of Photoperiod and Nitrogen Form on the Growth of Leaf Lettuce and Fluctuation of Nutrient Solution pH in Plant Factory Condition
2020 Volume 32 Issue 3 Pages 143-152
Details
2020 Volume 32 Issue 3 Pages 143-152
Beneficial effects of 24-h photoperiod and ammonium (NH4-N) fertilization on plant performance show potential for application in the production of high value-added vegetables that can only be produced in plant factories. In addition, lettuce is known to be relatively resistant to both 24-h photoperiod and NH4-N compared to other vegetables. Therefore, in this study, we focused on the interactive effects of photoperiod (12 h or 24 h) and nitrogen form on growth and rhizosphere pH of leaf lettuce cultivated in a plant factory condition. Nitrogen treatments consisted of five nutrient solutions containing the same nitrogen concentration (8 mM) but differing in the NH4-N to nitrate (NO3-N) ratio (0:100, 25:75, 50:50, 75:25, and 100:0). Under the 12-h and 24-h photoperiods, the pH of the nutrient solution declined to 3.0-3.8 when plants were supplied NH4-N, regardless of the NH4-N: NO3-N ratio. The onset of pH decrease was earlier under the 24-h photoperiod than the 12-h photoperiod, which reflected the differential timing of acceleration in plant growth. Shoot fresh weight at harvest was not significantly different among nitrogen sources containing 0 % to 75 % NH4-N under the 12-h photoperiod. On the other hand, early growth under the 24-h photoperiod was superior with nitrogen sources containing 25 % or 50 % NH4-N, but growth gradually stagnated probably because of low-pH stress; consequently, shoot weight at harvest was highest in plants supplied with 0 % NH4-N and tended to decline with increase in proportion of NH4-N. Therefore, little or no positive effect on yield with extension of the photoperiod was observed under NH4-N percentages ranging from 25 % to 100 %. However, the 24-h photoperiod and NH4-N interacted cooperatively to promote leaf greenness.
