Change in soil mineral nitrogen and respiration following tree harvesting from an agrisilvicultural system in Sweden

The effect of tree harvesting on soil mineral nitrogen and microbiological activity were investigated in an agrisilvicultural system consisting of wheat cultivated along the sides of a poplar plantation in Sweden from 1993 to 1995. Sampling for mineral nitrogen was carried out in three layers down to 90 cm at two distances, near (0.5-1.5 m) and far (4.0-5.0 m) from rows of standing, ST, and harvested trees, HT. Sampling for basic respiration and substrate-induced respiration was carried out in the 0-10 cm layer in 1993 and in the 0-10 cm and 10-20 cm layers in 1994 at the same distances from trees. There was a higher concentration of ammonium and lower concentration of nitrate closer to trees, indicating an efficient uptake of nitrate by trees and enhanced N mineralization close to trees. Shortly after tree harvesting, there were higher concentrations of nitrate and ammonium in the 0-30 cm soil layer near the harvested trees than near standing trees, suggesting a decrease in nitrogen uptake by tree roots. The soil microbiological activity was lower in the harvested than the standing plots of trees, which is considered as an indication of the important role of root exudates in maintaining a larger microbial biomass close to trees.