Comparison of Spurway and saturated media extracts of soilless media

Abstract

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 increasing concentrations of Ca and Mg were detected in SME, but not SPUR. SME and SPUR indicated generally similar trends for NH4 + and NO3 ‐. Both media extracts were correlated with plant tissue for P, but not other elements. Media EC increased with time and with increasing fertilizer concentration. EC in all media fertilized with 250 ppm N exceeded 4.5 dS/m at the final harvest. Plant growth responded positively to increasing fertilizer concentration to 150 ppm N in two media, probably due to increased accumulation of both N and P. Decreased growth at 250 ppm was related to high EC.