Growth Response of Hakonechloa macra (Makino) `Aureola' to Fertilizer Formulation and Concentration, and to Dolomitic Lime in the Potting Mix

Abstract

The shade-tolerant, variegated grass Hakonechloa macra `Aureola' is a valuable ornamental. In an experiment replicated in two growing seasons, Hakonechloa plants were fertilized at each irrigation (fertigation) with factorial combinations of three fertilizer formulations (N:P molar ratios 5:1, 10:1, and 20:1) at five N concentrations (2, 4, 8, 16, and 32 mmol·L-1), along with an unfertilized control, to determine the effect of N:P ratio and N concentration on vegetative growth and to establish fertility guidelines for production. Root dry weight and tiller bud growth increased slightly as N:P ratio increased. Fertilizer N concentration of 16 mmol·L-1 promoted the most shoot growth, whereas the number of tiller buds and root growth were greatest at 2 and 4 mmol·L-1 N. No interaction occurred between N:P ratio and fertilizer concentration. Results indicate that an N concentration of 8 mmol·L-1, with an N:P ratio of 10:1 or 20:1 is optimal for production of Hakonechloa. At this fertilizer concentration, the mean electrical conductivity of extracts obtained by a solution displacement extraction (pour-through) procedure was 2.3 ± 0.45 dS·m-1 (mean ± standard deviation). Tissue nutrient concentrations of N, P, K, Ca, and Mg were (in mg·g-1): 24.0, 2.8, 14.3, 2.1, and 2.1, respectively. In a concurrent study, Hakonechloa plants were grown in pine bark: peat: sand mix with dolomitic lime added at 0, 1.2, 3.6, and 9.5 kg·m-3 producing pH ranging from ≈4.5 to 7.2. Growth of Hakonechloa was greatest with no lime (pH 4.5) and declined markedly as the rate of lime increased. Concentrations of N, P, and K in shoot tissue were greatest at a pH between 4.5 and 5.6 (0 and 1.2 kg·m-3 dolomitic lime). These findings clearly support recommending production of Hakonechloa in soilless potting mix with pH ≈4.5 and constant fertigation with N at 8 mmol·L-1.