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Using TDR to Estimate Hydraulic Conductivity and Air Entry in Growing Media and Sand

^a Département des sols et de génie agroalimentaire, Université Laval, Sainte-Foy, QC, Canada G1K 7P4
^b SAGAH-Institut national de la recherche agronomique, Centre d'Angers and Institut national d'horticulture, 42 Georges Morel, C.P.57, Beaucouzé 49071 France
^c Unité de science du sol. – Domaine St-Paul – Site Agroparc Avignon, 84914 France

View larger version (13K): [in a new window]   Fig. 1. Possible water content at different locations following wetting, (A) saturation and (B) drainage; t represents different times, x(t), the position of the wetting front at time t, L is the length of the column, and xa is the point of air entry.

View larger version (19K): [in a new window]   Fig. 2. Schematic representation of the sequential water content measurements ([t],s,i,c) performed to estimate Ks and a.

View larger version (38K): [in a new window]   Fig. 3. Experimental set-up used to perform the measurements.

View larger version (25K): [in a new window]   Fig. 4. Calibration curves obtained using (A) the CS-615 and (B) the Tektronix 1502-C instruments. Mineral refers to substrates with <0.20 kg kg-1 of organic matter content, and organic, with 0.20 kg kg-1 of organic matter content and more.

View larger version (16K): [in a new window]   Fig. 5. Examples of the relationships obtained between the position of the wetting front [L-x (t)] and time.

View larger version (25K): [in a new window]   Fig. 6. Relationship between the Ks estimates obtained under transient-state conditions with TDR (A.2), under steady-state conditions with an infiltrometer after a rapid resaturation with a pulse of water (A.4), under steady-state conditions with an infiltrometer after prolonged resaturation (B.1), and the Ks estimate obtained under steady-state conditions following wetting under tension (A.3).

View larger version (20K): [in a new window]   Fig. 7. Variations in air pressure recorded for different growing media during desorption in A.5.