Plug seedlings: Salinity tolerance, pre-plant nutritional requirements, and species effects of substrate pH

Nutritional management plays an important role in control of plug seedling quality. Special attention should be paid to fertilizer salinity and root substrate pH.; The pH of root substrate can be altered by the nutrient uptake process of plants. Seedling effect on unlimed paper substrate pH varied across 25 taxa from a maximum rise of 1.4 units with zinnia (Zinnia elegans Jacq.) to a decline of 1.1 units with tomato (Lycopersicum esculentum Mill.) in the interim from sowing to separation of cotyledons. In a peat moss:perlite substrate, 11 taxa altered substrate pH over a range of 0.6 units, much lower than on paper substrate. Taxa that tended to raise peat moss:perlite substrate pH regardless of fertilizer type or time included pansy (Viola × wittrockiana Gams.), petunia (Petunia × hybrida Vilm.-Andr.), and vinca (Catharanthus roseus G. Don) while those that lowered pH were celosia (Celosia cristata L.), tomato, and zinnia.; Experiments were conducted to determine the value of N, P, K, and S as pre-plant nutrients with the anticipation that some could be eliminated to alleviate the high salinity problem in many substrates. Impatiens ( Impatiens wallerana L. ‘Accent Rose’) and gomphrena ( Gomphrena globosa. L. ‘Buddy’) were tested. Omission of N yielded the most desirable compact seedling and bedding plant qualities and minimal delay in bedding plant flowering. Omission of P or all four nutrients yielded larger reductions in seedling size than omission of N and heavy delay in bedding plant flowering. Since N omission lowered the salt level of substrate more than P omission and had less negative impact on subsequent bedding plant flowering than the other two treatments, N omission would be the more desirable of the three.; Experiments were conducted to evaluate fertilizer salt effects on growth and quality of plug seedlings. Two systems of hydroponics and plug root substrates were used during the study. Reduced water uptake occurred at relatively low fertilizer salt levels followed by reduced height and shoot fresh weight at intermediate levels and decreased shoot dry weight at very high salt levels. Growth responses of seedlings to fertilizer salinity first appeared as growth stimulation at a relative low range of fertilizer concentrations. (Abstract shortened by UMI.)...