Substrate water status and evapotranspiration irrigation scheduling in heterogenous container nursery crops

A study was conducted to determine the effects of implementing different irrigation scheduling methods on heterogeneous container hardy ornamental nursery stocks. Four ornamental shrub species were grown in the same irrigation sector during the summer of four consecutive years (2007–2010): Forsythia × intermedia, Photinia × fraseri, Prunus laurocerasus L. and Viburnum tinus L. Automated drip irrigation based on either substrate water status (SW) or calculated crop evapotranspiration (ET; MODEL) was compared with “typical” timer-controlled irrigation (TIMER). In TIMER treatment, containers were irrigated based on grower management. In SW treatment, irrigation was controlled either by a water-filled tensiometer (2007) or by a dielectric soil moisture sensor (2008–2010) placed in one pot with a Prunus plant, the species with intermediate water need as found in preliminary work. In MODEL treatment, irrigation was controlled on the basis of the species with the greatest ET. Crop ET was calculated multiplying reference ET (ET0) by a species-specific crop coefficient (KC), which in turn was estimated from plant height. In all treatments, pre-irrigation substrate water deficit was lower than the plant available water in the container. Compared with TIMER treatment, SW and MODEL irrigation scheduling reduced considerably both water use (−21% to −40%) and nutrient emission (−39% to −74%) with no significant effect on plant growth and quality. Water saving resulted from a reduction of irrigation frequency and leaching fraction (water leached/water applied). Wireless sensor network technology and near/remote monitoring techniques can facilitate the application of plant-driven irrigation scheduling in commercial nurseries, where generally hundreds of plant taxa are cultivated in many independent irrigation sectors.