George C. Elliott

pH management in container media

Abstract Addition of lime to increase pH is generally required for soilless media based on acidic organic materials. Media pH may decrease over time as the result of addition of acidic fertilizers. The objectives of this research were to characterize reactions of conventional or finely ground limestone in soilless media and to compare resistance to acidification in soilless media amended with conventional or finely ground limestone. Various soilless media were amended with each type of lime at rates from 1 to 16 kg/m3 and incubated eight weeks at 20°C. Subsamples were removed and pH was measured in saturated slurries. About half as much finely ground limestone as conventional lime was required to adjust pH to 6.0 within one week after mixing and wetting. Neither initial nor final pH of unlimed peat‐rockwool mixes could be predicted from pH of components. In successive experiments with poinsettias (Euphorbia pulcherrima) and New Guinea Impatiens (Impatiens xhybrida), three media were amended with each type...

Growth response of Alstroemeria ‘Parigro Pink’ to phosphate supply in vitro

Rhizome tip explants of Alstroemeria ‘Parigo Pink’ were established on modified Murashige & Skoog medium with P added as KH2PO4 at 0, 0.01, 0.05, 0.25, 1.25 or 2.5 mM. Cultures were transferred to fresh media every 4 weeks. Five explants were harvested from each P treatment after 3, 5, 7, 9 and 11 weeks in culture. Explants were separated into rhizome and shoot, weighed, dried and wet-ashed. Phosphorus content of the ash was determined colorimetrically. Explants supplied 1.25 or 2.5 mM P produced significantly more shoots and growing points, and greater fresh weight of rhizomes and shoots, than those provided with lower P concentrations. Phosphorus accumulation rates in shoots in the two highest P treatments were significantly greater than in the lower P treatments. Shoot tissue P concentrations greater than 7 mmol kg-1 fwt evidently are required for maximum in vitro growth of Alstroemeria ‘Parigro Pink’. Explants provided the two highest P treatments partitioned a greater proportion of fresh weight and total P to shoots vs rhizomes than lower P treatments.

Comparison of Spurway and saturated media extracts of soilless media

Abstract Seedlings of Catharanthus roseus ’Grape Cooler’ transplanted into 120‐cm3 cell packs of three commercial potting media were fertilized at each irrigation in flood and drain trays with commercial 20N‐4.4P‐17K fertilizer at concentrations of 50, 150, or 250 ppm nitrogen (N). Media samples were obtained 2, 3, 4 and 5 weeks post transplant. The contents of four cells from each of two replications were airdried, mixed, and sifted to pass a 2 mm sieve. Concentrations of calcium (Ca), magnesium (Mg), potassium (K), phosphorus (P), ammonium (NH4 +), and nitrate (NO3 ‐) were measured in Spurway (SPUR) and Saturated Media (SME) extracts. Electrical conductivity (EC) was measured in SME extracts. Leaf samples obtained four weeks post transplant were analyzed for all essential elements. Highly significant correlations were obtained for nutrient concentrations in SME and SPUR, but the coefficient of determination (r2) for linear regressions ranged from 0.34 for Ca to 0.77 for NH4 +. Trends over time for incre...