One-year-old seedlings of Helleborus x hybridus Hort. Ex Vilmorin (Lenten rose) were potted into 3.8 liter (#1) containers filled with a pine bark substrate amended with one of five rates of dolomitic limestone [0, 1.4, 2.7, 4.1, or 5.4 kg/m3 (0, 3, 6, 9, or 12 lb/yd3)]. Substrate pH responded quadratically with increasing rate of dolomitic limestone (DL) producing a range of substrate pH from 4.5 to 6.9. Nitrogen application rates (NARs) ranging from 10, 20, 40, 80, and 160 mg/liter were applied with every irrigation. Top dry weight was affected by NAR, DL, and NAR × DL rate interaction. When no DL was added to the substrate, top dry weight increased quadratically with increasing NARs with maximum dry weight occurring with N at 124 mg/liter. However, when the substrate was amended with DL at 1.4, 2.7, 4.1, or 5.4 kg/m3 (3, 6, 9, and 12 lb/yd3) top dry weight increased linearly with increasing NARs with maximum top dry weight of 15 g to 16 g (0.53 oz and 0.56 oz) occurring with N at 160 mg/liter. Contrast analysis comparing DL rates within each NAR revealed DL rates of 1.4, 2.7, 4.1, and 5.4 kg/m3 (3, 6, 9, and 12 lb/yd3) produced greater top growth compared to growth at the DL rate of 0 kg/m3 (0 lb/yd3) at NARs of 40, 80, and 160 mg/liter. Furthermore, when fertilized with N at 40, 80 or 160 mg/liter, top dry weight produced with DL rates of 1.4, 2.7, 4.1, and 5.4 kg/m3 (3, 6, 9, and 12 lb/yd3) did not differ within each NAR. Root dry weight was unaffected by NARs and NAR × DL rate interaction. Rate of DL affected root dry weight with the largest increase in root growth occurring with DL between 0 kg/m3 and 1.4 kg/m3 (0 lb/yd3 and 3 lb/yd3). Root-to-top ratio (RTR) responded quadratically with increasing NAR with the lowest RTR occurring with N at 140 mg/liter. Foliar N, P, K, Ca, Mg, S, and Fe concentrations were unaffected by rate of DL and NAR × DL rate, whereas foliar N, P, K, Ca, Mg, and S were affected by NARs. Foliar N, P, K, and S concentrations responded quadratically to increasing NARs; foliar Ca and Mg concentrations were linear; and foliar Fe concentration was unaffected by NARs.
This research was funded, in part, by the North Carolina Agricultural Research Service, Raleigh, NC 27695-7643, and by a grant from the Perennial Plant Association, 3383 Schirtzinger Rd., Hilliard, OH 43026. Appreciation is extended to William M. Reece for technical assistance and to Pine Knot Farm Perennials, Clarksville, VA, for providing plants.
2Lecturer and Professor, respectively.