Consequences of root development on the evolution of hydraulic properties of peat growing media under a constant and optimal water regime
Résumé
The impact of root growth on the hydraulic properties of a fine (0~10 mm) and a coarse (20~40 mm) peat substrate was investigated under optimal water retention, i.e., at a constant water potential of -1 kPa. ‘Knock Out’ Rosae was grown in 1.1-L cylindrical containers for 110 days in a greenhouse under controlled climate and fertilization conditions. Water retention, unsaturated hydraulic conductivity, air diffusivity, root biomass and volume, and shoot weight were measured. Results indicated a final root volumetric content of 0.054 and 0.064 m3 m-3 in the fine and the coarse peats that were closed to the peat content in the pots (0.069 m3 m-3). As a consequence, from day 0 to day 110, the total porosity, the easy available water and especially the air filled porosity decreased. However, the unsaturated hydraulic conductivity K(?) did not significantly change whereas fine and coarse peats respectively showed a decrease and an increase in the gas diffusivity. The decrease in gas diffusivity for fine peat is due to the decrease in air filled porosity without significant change in pore tortuosity, whereas the large decrease in tortuosity for coarse peat (as compared to fine peat) lead to an increase in gas diffusivity, even if the air filled porosity weakly decreased in the other hand. More generally, results confirmed that hydraulic conductivity and air diffusivity have to be considered as the most relevant parameters for irrigation management.