Effects of nitrogen application on growth, stomatal conductance, transpiration, and chlorophyll content were studied in Spathiphyllum Schott 'Sensation' grown in sphagnum peat (SP)- and coir dust (CD)-based media with top-irrigation or subirrigation. Maximum shoot dry weight occurred at 8 mM N in plants grown in SP-based medium under top-irrigation and subirrigation, and in CD-based medium under subirrigation. For plants in CD-based medium under top-irrigation, maximum shoot dry weight was obtained at 16 mm N. In SP- or CD-based medium, shoot dry weight was greater at 4 and 8 mm N under subirrigation than under top-irrigation. Stomatal conductance and transpiration were reduced by nitrogen deficiency (0 N), greatly enhanced by 4 mm N, and decreased gradually at higher N levels. Chlorophyll content increased with increasing N concentration up to 8 mm. The percentage of maximum total dry weight increased quadratically as leaf N content increased from 1.5% to 3.5%. Nitrogen at 16 and 32 mm increased the number of leaves with marginal necrosis. Reduced growth and more leaves with marginal necrosis occurred in SP- or CD-based media with EC > 1.25 dS·m-1 in the middle and bottom layers.
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