Abstract

An experiment with four volumes of irrigation and five controlled-release fertilizers (CRFs) was conducted to evaluate effects on plant growth and mineral nutrient content. Rooted cuttings of Cotoneaster dammeri ‘Skogholm’ and seedlings of Rudbeckia fulgida ‘Goldsturm’ were grown in 3.8 liter (4 qt) containers in a pine bark:sand substrate (8:1, by vol) incorporated with 3.5 g (0.12 oz) N per container with one of the following five CRFs: Meister 21N–3.5P–11.1K (21–7–14), Osmocote 24N–2.0P–5.6K (24–4–7), Scotts 23N–2.0P–6.4K (23–4–8), Sustane 5N–0.9P–3.3K (5–2–4) or Woodace 21N–3.0P–9.5K (21–6–12). Irrigation volumes of 200 ml (0.3 in), 400 ml (0.6 in), 800 ml (1.1 in), or 1200 ml (1.7 in) were applied once daily (single) or in two equal applications with a two hr interval between irrigation allotments (cyclic). All measured variables were unaffected by irrigation application (cyclic or single). Top dry weight of cotoneaster increased quadratically with increasing irrigation volume for all CRFs. Maximum top dry weight was obtained with 612 ml (0.8 in), 921 ml (1.3 in), 928 ml (1.3 in), 300 ml (0.6 in), or 909 ml (1.3 in) for plants fertilized with Meister, Osmocote, Scotts, Sustane, and Woodace, respectively. Osmocote, Scotts, and Woodace produced 90% of maximum top weight over a wide range of irrigation volumes [≈ 550 ml (0.8 in) to 1200 ml (1.5 in)]. Stomatal conductance of cotoneaster fertilized with Osmocote 24–4–7 increased linearly with increasing volume of irrigation, whereas net photosynthetic rate increased quadratically and was highest at 800 ml (1.1 in). All CRFs, excluding Sustane, had similar dry weights when irrigated with 200 ml (0.3 in). At 800 ml (1.1 in) and 1200 ml (1.7 in), cotoneaster fertilized with Osmocote 24–4–7 and Scotts 23–4–8 produced greater top dry weight compared to Meister, Sustane, and Woodace. Top dry weight of rudbeckia increased quadratically with increasing irrigation volume regardless of CRFs. Maximum dry weight was produced with 1160 ml, 931 ml, 959 ml, 1091 ml, or 1009 ml for plants grown with Meister, Osmocote, Scotts, Sustane, or Woodace, respectively. Ninety percent of the maximum top dry weight of both species within each CRF could be obtained with a 40% reduction in irrigation volume. Nitrogen content of cotoneaster and rudbeckia were unaffected by irrigation volume, whereas P and K content, depending upon CRF and plant, was reduced at low irrigation volumes.