Articles
SUPPLEMENTAL IRRADIANCE CONTROL OF PETUNIA SEEDLING GROWTH AT SPECIFIC STAGES OF DEVELOPMENT.
Emerged seedlings were treated with supplemental 24 h supplemental HPS irradiation.
The critical period for the irradiation of petunia seedlings in the greenhouse with high pressure sodium vapor lamps (HPS), in order to obtain an optimum increase in seedling weight and a decrease in the number of days to flower, was found to be the period 10 to 15 or 10 to 20 days after germination.
During this period, the first and second true leaves were expanding.
Providing supplemental irradiance prior to first leaf expansion or following the expansion of three leaves was often 30% less effective.
Treatment durations of 20 days further increased seedling size but to a lesser degree than the initial 5 or 10 day treatment.
Supplemental root zone heating combined with supplemental HPS irradiance of approximately 120 μmol m-2s-1 increased rates of seedling development.
As the ambient light conditions increased from January through April, the efficacy of the supplemental HPS treatments diminished.
The decrease in treatment efficacy was due to increased growth of the untreated controls.