Availability of nitrogen and phosphorus in Norway spruce forest floors fertilized with nitrogen and other essential nutrients

Abstract

The influence of various fertilization treatments on the availability of N and P in the forest floor was studied in a Danish Norway spruce ( Picea abies (L.) Karst.) stand. The treatments included fertilization with N alone in two doses, N combined with lime and other essential nutrients, and lastly lime and nutrients other than N. We tested the hypotheses that fertilization with N alone would increase the availability of N and P in forest floors, and that fertilization with N in combination with lime and other nutrients would further increase N and P availability. Extractable and mineralizable NH 4–N, NO 3–N, and PO 4–P 2 and 3 years after application of fertilizers were the indicators of N and P availability. Microbial activity as reflected by basal respiration rates was not affected by any of the fertilization treatments. The extractable and mineralizable amounts of N both indicated that N fertilization did not increase the availability of N in forest floors. Combined fertilization with N and other essential nutrients including lime reduced N availability, and application of lime and other nutrients than N resulted in the lowest N availability of all treatments. Nitrification rates were, however, increased after application of the highest amount of N and after application of lime. The replication over 2 years showed a consistent pattern, and treatment responses mainly occurred in the LF layer of forest floors. Phosphorus availability increased following liming and fertilization with nutrients other than N; this occurred in the H layer of forest floors. The results did not support the hypothesis that N fertilization increases N availability in the forest floor. There was also no evidence of a sustained positive effect on N availability of combined fertilization with N, lime, and other nutrients. In fact, N availability was reduced by the application of other nutrients and lime, whereas the study suggests that this treatment may positively affect P availability in a longer-term perspective.