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Factors Contributing to Changes in Plant Available Nitrogen across a Variable Landscape

^a Dep. of Soils and Plant Nutrition, Rubber Research Institute of Sri Lanka, Dartonfield, Agalawatta, Sri Lanka
^b Dep. of Land Resource Science, Univ. of Guelph, Guelph, ON, Canada, N1G 2W1

View larger version (33K): [in a new window]   Fig. 1. Digital elevation map indicating the experimental sites in the 1999 and 2001 seasons (site A) and the 2000 season (site B). The five rows of dots across the slope in a given site indicate the landscape positions (from top to bottom: summit, shoulder, backslope, footslope, and toeslope).

View larger version (28K): [in a new window]   Fig. 2. Distribution of rainfall during the growing period in the 1999, 2000, and 2001 seasons. The rainfall data exceeded the y-axis maximum on 6 Sept. 1999 (70.0 mm) and on 19 Aug. 2001 (63.8 mm).

View larger version (30K): [in a new window]   Fig. 3. Variation in average daily soil temperatures (°C) at 5- and 20-cm depths in three contrasting landscape positions during first week of July, August, September, and October 2000.

View larger version (31K): [in a new window]   Fig. 4. Pattern of plant available N accumulation throughout the 1999, 2000, and 2001 growing seasons in three contrasting landscape positions. The vertical bars indicate the standard error.

View larger version (25K): [in a new window]   Fig. 5. Relationship between the seasonal average water-filled pore space (SAWFPS) and organic carbon content () with their regression equations in the 1999, 2000, and 2001 seasons. This also illustrates the distribution of SAWFPS with respect to the lower () and upper () limits of the nonlimiting water range (NLWR) (Drury et al., 2003) in the 1999 and 2000 seasons. Because the textural data for the 2001 season were not available, the NLWR could not be calculated.