Modelling the carbon and nitrogen balances of direct land use changes from energy crops in Denmark: a consequential life cycle inventory

Abstract

This paper addresses the conversion of Danish agricultural land from food/feed crops to energy crops. To this end, a life cycle inventory, which relates the input and output flows from and to the environment of 528 different crop systems, is built and described. This includes seven crops (annuals and perennials), two soil types (sandy loam and sand), two climate types (wet and dry), three initial soil carbon level (high, average, low), two time horizons for soil carbon changes (20 and 100 years), two residues management practices (removal and incorporation into soil) as well as three soil carbon turnover rate reductions in response to the absence of tillage for some perennial crops (0%, 25%, 50%). For all crop systems, nutrient balances, balances between above-and below-ground residues, soil carbon changes, biogenic carbon dioxide flows, emissions of nitrogen compounds and losses of macro-and micronutrients are presented. The inventory results highlight Miscanthus as a promising energy crop, indicating it presents the lowest emissions of nitrogen compounds, the highest amount of carbon dioxide sequestrated from the atmosphere, a relatively high carbon turnover efficiency and allows to increase soil organic carbon. Results also show that the magnitude of these benefits depends on the harvest season, soil types and climatic conditions. Inventory results further highlight winter wheat as the only annual crop where straw removal for bioenergy may be sustainable, being the only annual crop not involving losses of soil organic carbon as a result of harvesting the straw. This, however, is conditional to manure application, and is only true on sandy soils.

Carbon Inputs from Miscanthus Displace Older Soil Organic Carbon Without Inducing Priming

“…This climate change is primarily driven by increasing concentrations of greenhouse gases (GHGs) in the atmosphere, and in particular carbon dioxide (CO 2 ) emissions resulting from burning fossil fuels for energy generation [3]. Bioenergy crops like Miscanthus have the potential to displace some of our dependency on non-renewable fossil fuels [4,5] but the relative advantage of bioenergy is largely influenced by realised yields and carbon (C) sequestration in pools that remain after the aboveground biomass has been harvested [6,7]. Even a relatively modest 1 t C ha −1 yr −1 [8] increase in soil C stocks can improve the GHG footprint of Miscanthus by 314 g CO 2 -eq kWh −1 , assuming electricity generation in a steam-turbine power station averaging 30 % Electronic supplementary material The online version of this article (doi:10.1007/s12155-016-9772-9) contains supplementary material, which is available to authorized users.…”

How to manage uncertainty in future Life Cycle Assessment (LCA) scenarios addressing the effect of climate change in crop production

“…Examples of application of this tool in crop production under current climate conditions are detailed, e.g. in Hamelin et al (2012) and Knudsen et al (2014). Soil C balance is influenced by local factors, e.g.…”

“…The effects of diseases, weeds and insects on crops are accounted for in current LCA considering the use of pesticide input as reported in the National statistics (Hamelin et al, 2012;Roer et al, 2012) or according to farm-specific practices (Fedele et al, 2014). Different approaches can be found in literature to describe the processes from pesticide spraying to emissions in soil, water and air, according to the definition of the boundaries between ecosphere and technosphere for agricultural field and its soil.…”

“…The definition of the baseline scenario for spring barley under Danish conditions (step 1) is quite univocal, since national databases (Knowledge Centre for Agriculture, 2013) and published data valid for Denmark (Hamelin et al, 2012) are available and can be used to describe the adopted field operations, as well as the amount and type of fertilizers and pesticides. The choice of LCIA method is more ambiguous; if a method that does not distinguish different value sets, e.g.…”

Global warming potential impact of bioenergy systems

“…minimizes the global warming dLUC impact thanks to the higher yield (and thus C uptake from the atmosphere) which also determines a beneficial increase of the soil organic carbon stock (SOC). Furthermore, requirement of fertilizers for these crops is low [10] leading to lower eutrophication impacts [11]. For these reasons, this study focuses only on perennials.…”