Spatial and temporal dynamics of water in the root environment of potted plants on a flooded bench fertigation system

The relationship between evapotranspiration of potted plants on a flooded bench fertigation system and the realised distribution of water in the root zone was studied in detail for a range of fertigation schedules. The physical characteristics of the peat-based potting medium are described by models commonly used in soil physics. The functioning of the substrate in practical situations was highly affected by hysteresis in the water retention characteristic. Daily evapotranspiration of Ficus benjamina plants varied from 0.4 to 4.1 kg m-2 day-1, of which 19-41% was lost by evaporation. Water uptake by plant roots resulted in near hydrostatic equilibrium conditions as long as the volumetric water content was above 0.22. Lower average water contents resulted in locally drier conditions in the root environment. The absorption of water during irrigation depended on the soil physical conditions and increased with decreasing volumetric water content before flooding. The majority of the water absorption occurred within the first minutes, making frequent fertigation more effective than increasing the duration. Actual buffer capacity of the potting medium is defined and by combining measured absorption during flooding with data on evapotranspiration, we indicate how minimum requirements of the fertigation schedule can be derived.