Nitrogen Mineralization and Organic Matter Decomposition in Scots Pine Humus

Nitrogen deficiency in many northern coniferous forests is associatedwith increasing age of the crop and is thought to be due toa slow rate of release of available nitrogen from the organiclayers of the forest floor. Practical ways of stimulating nitrogenrelease from this material by applications of nitrogen, phosphorus,and lime are being studied in a 40-year-old crop of nitrogen-deficientScots pine (Pinus sylveitris L.) at Culbin Forest, Moray. Threeyears after lime and phosphorus treatments, and two years afterthe second fertilizer nitrogen application, significant treatmenteffects included both markedly higher pH values and increasedrates of organic matter decomposition on incubation (at 30 °Cfor 62 days) for humus from plots given lime and higher ratesof net production of mineral nitrogen on incubation for humusfrom plots given fertilizer forms of ammonium sulphate, urea,and ammonium nitrate. Only urea-treated humus still showed asignificantly higher total nitrogen content at this time, I.54per cent of organic matter compared with 141 per cent in untreatedmaterial.