Environmental Effects over the First 2½ Rotation Periods of a Fertilised Poplar Short Rotation Coppice

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 (NO 3 − ) was monitored with self-integrating accumulators over 6-month periods and the emissions of the greenhouse gases (GHG) nitrous oxide (N 2 O) and carbon dioxide (CO 2 ) were determined in closed gas chambers. During the first 4 years of the poplar SRC, most nitrogen was lost through NO 3 − 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 CO 2equ ) 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 N 2 O emissions from the soil was very low with an average of 0.61 kg N ha −1 year −1 (182 kg CO 2equ ) and were also not affected by N fertilisation over the whole study period. Real CO 2 emissions from the poplar soil were two orders of magnitude higher ranging between 15,122 and 19,091 kg CO 2 ha −1 year −1 and followed the rotation period with enhanced emission rates in the years of harvest. As key-factors for NO 3 − leaching and N 2 O emissions, the time after planting and after harvest and the rotation period have been identified by a mixed effects model.

Abiotic and biotic factors controlling fine root biomass, carbon and nutrients in closed-canopy hybrid poplar stands on post-agricultural land

“…Estimates from the boreal forest showed that fine root biomass and N content of Populus stands respectively averaged 4800 kg/ha and 46.7 kg N/ha in the 0–20 cm soil layer 13 . This is well above the measured range for live fine root biomass (581.3–1642.6 kg/ha) and N content (4.91–13.23 kg N/ha), which corresponds to observations from other poplar plantations in the temperate zone 37,38 . Such high fine root biomass in boreal poplar stands vs. temperate old-field plantations likely reflects climate-related limitations in soil resource availability and in nutrient uptake rate by roots as latitude increases 46 .…”

“…Previous field studies with planted poplars have reported different conclusions related to the effect of abiotic and biotic factors on fine root biomass 35–38,40,41 . Our regional-scale study, conducted in 14 year-old closed-canopy poplar plantations, provides evidence supporting the negative relationship hypothesis between soil fertility and fine root biomass 13 (Fig.…”

“…deltoides fine root biomass, and concluded that stand developmental stage was the factor with overriding importance. Developmental stage also affected fine root biomass of a poplar short-rotation coppice, but a strong negative effect of N fertilization on fine root biomass appeared during the 4 th growing season 38 . A recent greenhouse study also showed that a low N supply changed gene expression, modified root architecture and led to an increase in fine root biomass, thus providing evidence of a unique nitrogen-adaptative mechanism regulating hybrid poplar root growth in response to soil N supply 39 .…”

The Impact of Poplar Short Rotation Coppice on Topsoil Physical Properties and Related Water Conditions

“…The impacts of SRC on water resources have been widely studied [3][4][5][6][7]. Soil-related investigations have mainly focused on the impacts of SRC on soil ecology [8][9][10][11][12][13], whereas changes on soil physical properties have been poorly studied. Evaluations of soil properties mainly occurred as part of an assessment of site characteristics affecting SRC size, quality and sustainability of yields [14,15].…”

Influence of Tree Species, Harvesting Method and Storage on Energy Demand and Wood Chip Quality When Chipping Poplar, Willow and Black Locust

“…Trees planted on agricultural land present an opportunity for producing biomass sustainably and at the same time improving farm income. Fast-growing tree species such as poplar, willow and black locust cultivated in short rotation coppices (SRC) or agroforestry systems (AFS) offer not only considerable potential for producing plant biomass, but can also at the same time withdraw carbon from the atmosphere and store it in their biomass [1][2][3][4][5][6]. To be successful in competition with wood products from the forestry sector, various obstacles need to be overcome when expanding the cultivation of fast-growing agricultural timber crops.…”