Plant water relations and mineral nutrition of containerized nursery plants in relation to irrigation method

Cotoneaster dammeri C. K. Schneid. 'Coral Beauty' and (Forsythia ovata × Forsythia europaea Deg. and Bald.) Forsythia 'Northern Gold' were grown in 3.8-L containers in a softwood bark–peat–sand medium, using overhead, pulse, drip or subirrigation methods. N, P and K were supplied from Nutricote 16N-4.4P-8.1K (type 140) controlled-release fertilizer. Overhead sprinklers irrigated containers during two 45-min periods each day. Daily pulse irrigation was from sprinklers for four 7-min periods, and drip irrigation to individual containers occurred during two 5-min periods. For subirrigation, plants were placed on permanently saturated sand beds. Subirrigation resulted m significantly higher plant dry weights at the end of the growing season than all other treatments. Measured daily leaching volumes were greatest from overhead-irrigated containers, followed by drip- and then pulse-irrigated containers. Leaching from the subirrigated treatment was small and sporadic, occurring only after moderate rainfall. Shoot water potential (ψ T ) was measured at weekly intervals through the middle of the growing season. There were no differences in predawn or dusk ψ T values between treatments, but midday ψ T was generally lower in subirrigated plants. At the end of the growing season, electric conductivity of the medium was highest for subirrigation, intermediate for drip and pulse irrigation, and lowest for overhead irrigation. This pattern was repeated for foliar K levels. It appears that superior growth of subirrigated plants is due more to better nutrient retention in the medium than to any effect on plant water status. Key words: Capillary irrigation, nutrient leaching