NUTRITION AFFECTS PRETRANSPLANT AND POSTTRANSPLANT GROWTH OF IMPATIENS AND PETUNIA PLUGS

Pre- and posttransplant growth of plug seedlings is affected by the nu trition of the plants. The effects of weekly applications of nutrient solution with different N (8-32 mM) or P and K (0.25-1.0 mM) levels on the growth and nutrient composition of impatiens (Impatiens wallerana Hook. f.) and petunia (Petunia xhybrida hort.Vilm.-Andr.) plug seedli ngs were quantified. Impatiens and petunia pretransplant seedling grow th was most krapid with a NO3- concentration of 24 or 32 mM (N at 336 and 148 mg.L-1), while P and K had little effect. Increasing the N con centration in the fertilizer also increased shoot tissue N levels of b oth impatiens and petunia and decreased shoot P level of impatiens and K level of petunia. Posttransplant growth was most rapid in plants th at received N at 16 to 39 mM. Decreasing P and K from 1 to 0.25 mM in the pretransplant fertilizer reduced posttransplant growth. Shoot P le vel of impatiens 15 d after transplanting decreased from 6.9 to 4.8 mg .g(-1) as the pretransplant fertilizer N concentration increased from 8 to 32 mM, while N level increased from 18 to 28 mg.g(-1) as P and K fertilizer concentrations increased from 0.25 to 1 mm. Using posttrans plant growth as a quantitative norm for plug quality, the sufficiency ranges for tissue N level are 28 to 40 mg.g(-1) for impatiens and 30 t o 33 mg.g(-1) for petunia plugs. These results indicate that fertiliza tion programs for high-quality plug production should focus on N nutri tion, and that plugs can be grown with greatly reduced levels of P and K.