Optimized strategies for nitrogen fertilizer application in Populus plantations in the context of climate change mitigation

Nitrogen (N) fertilizer application increases biomass volume and enhances the carbon sequestration of forest stands. However, overused N fertilizers induce nitrous oxide (N2O), a greenhouse gas with a higher global warming potential than CO2. This study estimates the growth function of Populus stands based on field data, based on which the revised Faustmann model is used to evaluate the optimal rotation and the N fertilizer application rate under different scenarios. Results show that the stand volume is an increasing logarithmic-reciprocal function of the age and N fertilizer rate, and the increment by age is more significant and lasting. When the cost of N2O emissions is considered, the fertilization rate is substantially reduced; a higher carbon price decreases the fertilization rate but prolongs the optimal rotation. Overall, participation in forest carbon projects is economically beneficial even when the costs of greenhouse gas emissions are considered. The research outcomes provide insights into the interplays between the benefits and costs of N fertilizer applications and forest owners' behavior. The conclusions support the accounting of N2O emissions in protocols of forest carbon projects and a more ambitious mitigation goal to push the carbon price on a national scale market.