Growing Picea abies container seedlings in peat and composted forest-nursery waste mixtures for forest regeneration

The suitability of using composted forest-nursery waste as a component in growing medium was studied. Norway spruce [ Picea abies ( L.) Karst.] seedlings were grown in containers filled with sphagnum peat (100P), forest-nursery waste compost (100C) and in peat mixtures containing 25 or 50% compost by volume (75P25C and 50P50C, respectively). Morphological and chemical characteristics of the seedlings and the water and nutrient contents of the growing media were studied during 22 weeks of nursery cultivation. The seedlings were outplanted the following spring, and the survival and growth were followed for 3 years. Compost additions decreased seedling height, diameter and shoot dry mass, but root dry mass was the same in 100P and 75P25C after nursery cultivation. Foliar nutrient concentrations were optimal in all the seedlings, although foliar nitrogen content was lower the greater the proportion of compost in the medium. Compost additions did not affect the root-egress potential tested before outplanting. The 100P seedlings grew significantly more than the other seedlings during the first summer at the forest site. Thereafter, compost additions did not affect growth, but the final height and diameter were still the lowest in 100C. The results suggest that forest-nursery waste compost has potential to be used as a component of peat-based growing medium. However, specially adjusted nursery-cultivation practices need to be used for compost-containing media.