Nitrogen and energy balance of a short-rotation poplar forest system.

The mean annual dry matter production of a short-rotation poplar forest in the Netherlands was 14.4 tonnes ha-1 during a 5-year growing period. During the growing period trees took up 542 kg N ha-1 of which 64 % was in the bole and branches. In the 5th year denitrification was measured in undisturbed columns in the field by the acetylene-inhibition technique. An annual denitrification rate of 18 kg N ha-1 was estimated on the basis of the observed N2O profile. The system needed an annual input of 122 kg N ha-1 to balance the nitrogen budget. The energy balance showed that at the present dry matter production the system had a net output of 54 GJ ha-1 year-1. An increase in dry matter production to a maximum of 25 tonnes ha-1 year-1, possible by planting the trees at a higher density, would raise the net energy output to 97 GJ ha-1 year-1, in spite of higher energy inputs associated with fertilizer applications. (Abstract retrieved from CAB Abstracts by CABI’s permission