Environmental Effects over the First 2\xbd Rotation Periods of a Fertilised Poplar Short Rotation Coppice

Jürgen Kern,Antje Balasus,Wolf-Anno Bischoff,Sonja Germer,Andreas Schwarz,Martin Kaupenjohann,Manfred Forstreuter,Christian Ammon

doi:10.1007/s12155-017-9885-9

Abstract

A short rotation coppice (SRC) with poplar was established in a randomised fertilisation experiment on sandy loam soil in Potsdam (Northeast Germany). The main objective of this study was to assess if negative environmental effects as nitrogen leaching and greenhouse gas emissions are enhanced by mineral nitrogen (N) fertiliser applied to poplar at rates of 0, 50 and 75 kg N ha−1 year−1 and how these effects are influenced by tree age with increasing number of rotation periods and cycles of organic matter decomposition and tree growth after each harvesting event. Between 2008 and 2012, the leaching of nitrate (NO3−) was monitored with self-integrating accumulators over 6-month periods and the emissions of the greenhouse gases (GHG) nitrous oxide (N2O) and carbon dioxide (CO2) were determined in closed gas chambers. During the first 4 years of the poplar SRC, most nitrogen was lost through NO3− leaching from the main root zone; however, there was no significant relationship to the rate of N fertilisation. On average, 5.8 kg N ha−1 year−1 (13.0 kg CO2equ) was leached from the root zone. Nitrogen leaching rates decreased in the course of the 4-year study parallel to an increase of the fine root biomass and the degree of mycorrhization. In contrast to N leaching, the loss of nitrogen by N2O emissions from the soil was very low with an average of 0.61 kg N ha−1 year−1 (182 kg CO2equ) and were also not affected by N fertilisation over the whole study period. Real CO2 emissions from the poplar soil were two orders of magnitude higher ranging between 15,122 and 19,091 kg CO2 ha−1 year−1 and followed the rotation period with enhanced emission rates in the years of harvest. As key-factors for NO3− leaching and N2O emissions, the time after planting and after harvest and the rotation period have been identified by a mixed effects model.

Highlights

The global climate is affected by an increase of CO2 concentration in the atmosphere [1]
The response variable BNO3− leaching^ was log10-transformed after adding a constant of 0.1 to achieve normality of model residuals
The treatment variable Bfertilisation^ (0, 50, 75 kg N ha−1 year−1) and the additional predicting variables Bseason^, Brotation period^, and the interactions between Bfertilisation and season^ were included as fixed effects

Summary

Introduction

The global climate is affected by an increase of CO2 concentration in the atmosphere [1]. 10587 Berlin, Germany summit in December 2015, international consensus exists on the need to limit the global increase in temperature to 1.5– 2.0 °C and to achieve climate neutrality in the second half of this century [2]. One suitable strategy for mitigating the accumulation of CO2 in the atmosphere may be the production and use of energy from biomass produced in silvicultural and agricultural sites [3, 4] in combination with the build-up of stable carbon pools in the soil [5, 6]. Most promising biomass yields are expected from wood production via short rotation coppices (SRC) on nutrient-enriched arable land [7].

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