Dynamics of water and nutrients for potted plants induced by flooded bench fertigation : experiments and simulation

Dynamics of water and nutrients as affected by physical and chemical characteristics of a substrate, fertigation method and schedule, and plant uptake were studied for a flooded bench fertigation system for potted plants, through a detailed experimental study of the root environment and a simulation model.

Based on analogy with soils, a summary is given of the theory which describes the dynamics of water and nutrients in horticultural substrates. Existing simulation models based on this theory, so far mainly tested for field soils, were adapted to the flooded bench fertigation system. The model comprises three submodels: 1) one-dimensional vertical water transport, accounting for hysteresis, allocation of water uptake over depth, and conical shape of the pot, 2) solute transport, and 3) chemical equilibration accounting for cation adsorption and precipitation. The model requires evapotranspiration as a forcing function.

For a potting medium consisting of peat and perlite, physical characterization is discussed. Characterization dealt with the water retention characteristic, including hysteresis and the effect of repeated wetting and drying, and the hydraulic conductivity characteristic. Mathematical equations, frequently applied for description of physical characteristics of soils, were used to describe the physical characteristics of the potting medium. Cation adsorption of the potting medium was found to be affected by pH. A cation adsorption model is presented to calculate the composition of the adsorption complex in relation to the composition of the liquid phase.

Transpiration of Ficusbenjamina and evaporation from the potting medium are discussed with respect to fertigation schedule. Using tensiometers, dynamics of water induced by fertigation of given frequencies and durations and by evapotranspiration were measured. Nutrient balances and vertical distributions were studied for different fertigation schedules. These data were mainly used for validation of the simulation model.

The simulation model gave a fair description of the measured data. The volumetric water content in relation to fertigation schedule and measured matric head profiles between fertigations could be understood by studying the dynamic behaviour of the model. Hysteresis in the water retention characteristic significantly influenced the dynamics of water. Vertical distribution of cations was strongly affected by cation adsorption. The combined use of the experiments and the model deepened the understanding of the complicated interactions between evapotranspiration, fertigation schedule, physical and chemical characteristics of the potting medium, and geometry of the pot, in particular the height. It was concluded that considering one of these factors separate from the others is not advisable, since they are all important.