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

Abstract

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)