Site-specific growth and nutrition of planted Piceamariana in the Ontario Clay Belt. IV. Nitrogen loading response

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Abstract
Black spruce (Piceamariana (Mill.) B.S.P.) containerized seedlings were raised at high fertilizer regimes, i.e., "nutrient loaded," during greenhouse culture to assess whether increased preplant nutrient reserves improved site-specific outplanting performance. Growing media electrical conductivity levels during the greenhouse phase ranged between 0.9–1.2 and 0.3–0.6 dS/m for loaded and nonloaded seedlings, respectively. Although similar in total biomass and P and K content at rotation end, the loaded seedlings contained 78% more N than the nonloaded seedlings, demonstrating induced luxury consumption of N from loading. After overwintering, the seedlings were planted on intact potted surface soils from three ecological site types (upland Feathermoss, lowland Alnus, and lowland Ledum) of contrasting fertility. In the first growing season, N loading significantly increased height growth and dry matter production on all substrates; relative response was higher on the more N-deficient lowland sites. Plant nutrients were markedly diluted after establishment, except for N of nonloaded seedlings. The loading response was closely associated with the buildup of preplant N, which served as a critical nutrient source for internal retranslocation to new growth. Loading stimulated not only N uptake after outplanting, but also uptake of other nutrients presumably because of the expanded root system with this treatment. Balanced nutrient loading offers a cost-efficient alternative to field fertilization by promoting outplanting performance of container stock, and by avoiding competition response and operational constraints often associated with on-site fertilization.
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