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Le Puy-Notre-Dame, France

Michel J.-C.,UPSP EPHOR | Qi G.,UPSP EPHOR | Charpentier S.,UPSP EPHOR
Acta Horticulturae | Year: 2013

The knowledge of physical properties over time in horticultural growing media is of vital importance for the effective management of irrigation and fertilization. Water retention, shrink/swell properties and water repellency of a Sphagnum peat growing medium were measured during several drying/wetting cycles with varying intensities (0↔-10 kPa, 0↔-32 kPa). Regardless of the intensity of drying, water retention and shrink/swell properties are mainly modified after the first drying process, resulting in an increase of density and a change in water retention (due to a consolidation in the range of potentials varying between 0 and -3 kPa), whereas these properties are not affected by the other cycles, even if hysteresis phenomena are always shown to take place. In parallel, water repellency (estimated by direct contact angles measurements between -15 and -32 kPa) also showed hysteresis phenomena and was also not affected by the number of cycles. Variations in drying intensity reveal a double porosity (inter and inner porosities), with an inflection point observed around -20 kPa. If hysteresis phenomena are due to the 'ink bottle' effect in the lowest suctions, water repellency can be considered as the most relevant parameters for explaining the hysteresis phenomena in the highest suctions (> -20 kPa).

Michel J.-C.,UPSP EPHOR | Cannavo P.,UPSP EPHOR
Acta Horticulturae | Year: 2014

The evolution of peat hydraulic properties in different parts of containers was studied during root growth. For that, a 4-month long experiment was carried out in a greenhouse in 1L-containers at constant water regime (-1 kPa water potential), with Rosa 'Knock Out'® and two different particle-size sphagnum peats, a fine one (0-10 mm) and a coarse one (20-40 mm). Every month, aerial biomass was quantified, whereas root biomass and distribution, water retention, relative gas diffusivity was studied in relation with the depth and the proximity of the container border. The study showed that root growth mainly influenced aeration properties (air filled porosity, relative gas diffusivity), with large differences regarding spatial distribution of roots. But the evolution of aeration properties depended on the peat particle size.

Qi G.F.,UPSP EPHOR | Michel J.-C.,UPSP EPHOR | Charpentier S.,UPSP EPHOR | Boivin P.,University of Applied Sciences and Arts Western Switzerland
Acta Horticulturae | Year: 2011

A new apparatus was developed for simultaneously and continuously measuring the water retention and shrink/swell properties of growing media during several drying/wetting cycles. Initial results obtained on peats show that water retention and shrink/swell properties are mainly affected by the first drying and rewetting cycle and remain quasi-constant thereafter, regardless of the intensity and the number of drying/wetting cycles. Hysteresis phenomena in water retention are always observed. The use of a wetting agent (as compared with water) in peat leads to the reinforcement of the physical stability of growing media and to the limitation of hysteresis phenomena in water retention for the highest suction values.

Michel J.-C.,UPSP EPHOR | Kerloch E.,UPSP EPHOR | Bozon E.,UPSP EPHOR | Cannavo P.,UPSP EPHOR
Acta Horticulturae | Year: 2013

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 m 3 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 Kθdid 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.

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