article id 123,
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                        Research article
                    
        
                                    
                                    
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                            In 1981–82 three field experiments were established with the aim of  elucidating (i) the growth response of middle-aged coniferous stands at  different fertilization intensities and, hence, the economic outcomes;  and (ii) the need to add nutrients other than nitrogen (N). Nutrient  additions were performed at intervals of two, four, six and eight years.  The experiments were established on typical podzolized and N-limited  mor-humus sites, two in Scots pine (Pinus sylvestris L.) stands and one  in a Norway spruce (Picea abies (L.) Karst.) stand, at three different  locations in Sweden. The ages of the stands were 65–70 years at the time  of establishment. Growth responses were calculated after a 22-year  study period. The growth responses were significant in all treatments.  The addition of nutrients other than N did not affect stem growth at any  of the sites. The growth response tended to increase with decreasing  application interval. The results also revealed that the efficiency of  fertilization is reduced as the interval between fertilizations is  shortened. Accordingly, the growth effect per kg of added N was  negatively correlated to fertilization intensity. The least intensive  fertilization regime (an eight-year interval) resulted in an average net  increase in C sequestration of 35 kg per kg N added. The profitability,  in terms of internal rate of return, the present net value at different  interest rates and the cost of production, i.e. the cost to produce one  extra m3 under the different N regimes, are presented and discussed.
                        
                
                                            - 
                            Jacobson,
                            Skogforsk, Uppsala Science Park, SE-75183 Uppsala, Sweden
                                                        E-mail:
                                                            staffan.jacobson@skogforsk.se
                                                                                        
                                                     
                                            - 
                            Pettersson,
                            Skogforsk, Uppsala Science Park, SE-75183 Uppsala, Sweden
                                                        E-mail:
                                                            fp@nn.se