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Spatial Variability of Substrate Water Content and Growth of White Spruce Seedlings

^a Direction de la recherche forestière, Ministère des Ressources naturelles et de la Faune, 2700, rue Einstein, Sainte-Foy, QC, G1P 3W8, Canada
^b Faculté de foresterie et de géomatique, Pavillon Abitibi-Price, Université Laval, Sainte-Foy, QC, GIK 7P4, Canada

View larger version (67K): [in a new window]   Fig. 1. Schematic of the experimental layout covering the area irrigated by two adjacent sprinklers and a total of 1820 air-slit containers (25–350A). *: Sprinklers : Air-slit containers that were not sampled : Air-slit containers (25–350A) that were sampled. Substrate moisture content was monitored by inserting double diode probes through the five central cavities of the container. The height and root collar diameter of the seedlings growing in these cavities were also measured on each of the sampling days. Ø and O: Containers that were sampled at the end of the growing season (27 Sept. 2001) for measurement of root and shoot dry mass and nutrient content analyses (3 plants/container). Ø: Containers that were sampled to quantify the amount of leachate.

View larger version (26K): [in a new window]   Fig. 2. Variation (a) of maximum and minimum daily air temperatures 2 m above the ground, (b) at the substrate surface and (c) in the rhizosphere, as well as the fluctuations in (d) relative humidity during the second growing season of air-slit containerized white spruce seedlings at Pampev Inc., a private forest nursery located in Saint-Louis-de-Blandford, QC, Canada (46° 25' N, 72° 00' W).

View larger version (24K): [in a new window]   Fig. 3. Daily and cumulative quantities of water received by the (2+0) white spruce seedlings in the form of precipitation (P) and irrigation (I). The arrows indicate the different sampling dates on which the substrate water content, seedling height and root collar diameter were measured. P* and I* indicate the total quantities of water received between two consecutive sampling dates, as precipitation and irrigation, respectively.

View larger version (23K): [in a new window]   Fig. 4. Omnidirectional semi-variograms of the substrate water content in the rhizosphere of the (2+0) white spruce seedlings. The table includes the estimated theoretical model parameters for each of the sampling days (a: range; C0: nugget effect; C0 + C1: total variance; R2: cross- validation; C1/(C0 + C1): spatial dependence; n: number of containers sampled). For each container sampled, the data represent the average substrate water content in the five central cavities through which the MP-917 probes were inserted.

View larger version (71K): [in a new window]   Fig. 5. Mapped representations of the substrate water contents. The interpolated values were determined for each of the sampling dates by kriging: (a) June 12, (b) June 27, (c) July 11, (d) August 11 and (e) 10 Sept. 2001.

View larger version (16K): [in a new window]   Fig. 6. Omnidirectional semi-variograms of the height of the (2+0) white spruce seedlings. The table indicates the estimated theoretical model parameters for each of the sampling days (a: range; C0: nugget effect; C0 + C1: total variance; R2: cross- validation; C1/(C0 + C1): spatial dependence; n: number of containers sampled). For each container sampled, the data represent the average height of the seedlings in the five central cavities through which the MP-917 probes were inserted.

View larger version (16K): [in a new window]   Fig. 7. Omnidirectional semi-variograms of the root collar diameter of the (2+0) white spruce seedlings. The table indicates the estimated theoretical model parameters for each of the sampling days (a: range; C0: nugget effect; C0 + C1: total variance; R2: cross- validation; C1/(C0 + C1): spatial dependence; n: number of containers sampled). For each container sampled, the data represent the average root collar diameter of the seedlings in the five central cavities through which the MP-917 probes were inserted.

View larger version (18K): [in a new window]   Fig. 8. Omnidirectional semi-variogram of (a) substrate water content integral fitted to the exponential model (C0 = 13.90, C0 + C1 = 46.30, a = 3.58, R2 = 0.80), as well as (b) its cross-validation between the observed and predicted values.

View larger version (54K): [in a new window]   Fig. 9. Kriged maps of (a) the height of the (2+0) white spruce seedlings on 10 Sept. 2001(spherical model) and (b) substrate water content integral (I) (omnidirectional model).