Nitrogen Transformations and Decomposition in Litter and Humus from beneath Closed-Canopy Sitka Spruce

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Abstract
Samples of litter and humus from beneath 10 m tall, closed-canopy Sitka spruce planted on a brown forest soil were incubated under both field and laboratory conditions to measure mineral nitrogen production and carbon dioxide evolution. Mineral nitrogen production in enclosed samples over 12 months was equivalent to 50 and 17 kg N ha −1 in litter and humus, respectively. Applications of fertilizer NPK (200 kg N ha −1 as ammonium nitrate, 100 kg P ha −1 as unground rock phosphate and 150 kg K ha −1 as potassium chloride), 18 months previously, decreased these values slightly, but stimulated the production of nitrate in both litter and humus. Compared with samples kept under laboratory conditions at 10°C, those incubated in the field at a similar mean temperature released less carbon dioxide and, in the case of fertilized humus produced smaller amounts of mineral nitrogen.