Medium-term effect of perennial energy crops on soil organic carbon storage

Abstract

The scope of this study was to evaluate the effect of perennial energy crops on soil organic carbon (SOC) storage. A field experiment was undertaken in 2002 at Anzola dell'Emilia (Bologna), in the lower Po Valley, Northern Italy. Five perennial energy crops were established on a land area which had been previously cultivated with arable crops for at least 20 years. The compared crops are: the herbaceous perennials giant reed and miscanthus, and the woody species poplar, willow and black locust, managed as short rotation coppice (SRC). SOC was measured in 2009, seven years after the start of the experiment, on an upper soil layer of 0.0-0.2 m and a lower soil layer of 0.2-0.4 m. The study aimed to compare the SOC storage of energy crops with alternative land use. Therefore, two adjacent areas were sampled in the same soil layers: i) arable land in steady state, cultivated with rainfed annual crops; ii) natural meadow established at the start of the experiment. The conversion of arable land into perennial energy crops resulted in SOC storage in the upper soil layer (0.0-0.2 m) ranging from 1150 to 1950 kg C ha -1 year -1 during the 7-year period. No significant differences were detected in SOC among crop species. We found no relationship between the harvested dry matter and the SOC storage. The conversion of arable land into perennial energy crops provides a substantial SOC sequestration benefit even when the hidden C cost of N industrial fertilizers is taken into account. While the SOC increased, the total N content in the soil remained fairly constant. This is probably due to the low rate of nitrogen applied to the perennial crops. However, our data are preliminary and the number of years in which the SOC continues to increase needs to be quantified, especially for the herbaceous species giant reed and miscanthus, with a supposedly long duration of the useful cropping cycle of 20 years or longer. IntroductionMany nations have formulated policies promoting the production and use of biomass to generate heat, power and liquid transport fuels (FAO, 2008). These policies were boosted by the perspective of the depletion of oil reserves and the concerns about energy security and global climate change (Koh and Ghazoul, 2008). Nonetheless, there is an intense debate in the scientific literature over the advantages and disadvantages of using cropland for producing biomass for energy. Some scientists, but certainly not all, believe that energy crops have a positive effect on the mitigation of CO2 emissions (Payne, 2010). Other authors have advised against the undesired effects of a widespread diffusion of energy crops on the global carbon cycle (Crutzen et al., 2008;Fargione et al., 2008;Searchinger et al., 2008). Two major aspects need to be considered when assessing the contribution of energy crops on meeting future energy demand with limited environmental impact: i) the amount of fossil energy that is required to produce each unit of renewable energy; ii) the greenhouse gas (GHG) emissions that are released in t...

Carbon sequestration potential in perennial bioenergy crops: the importance of organic matter inputs and its physical protection

“…Although the potential of switchgrass for SOC sequestration was highlighted in several studies (Ma, ; Liebig et al ., ; Schmer et al ., ), the different cropping managements (in terms of fertilization and irrigation) and analytical approaches to estimate the SOC stock variations limit the possibility to compare data across studies. Regarding miscanthus, results found in this study are partially in agreement with those reported by Ceotto & Di Candilo (), in which an annual SOC stock increment of 59 g C m −2 yr −1 was estimated, and are within the range reported by other authors from north Europe (78 and 112 g C m −2 yr −1 ; Hansen et al ., ).…”

“…Interestingly, higher annual SOC sequestration rates were observed under woody species (120, 99, and 95 g C m −2 yr −1 for black locust, willow and poplar, respectively) than under herbaceous species (80 C m −2 yr −1 for switchgrass and miscanthus). Similar annual SOC stock increments (from 58 g m −2 yr −1 up to 97.3 g C m −2 yr −1 ) were reported in a previous study carried out in the north of Italy, in which the same bioenergy species were confronted to an adjacent ploughed soil after 7 years from plantation (Ceotto & Di Candilo, ). Although the annual increments of SOC stock under willow and poplar observed in this study were in agreement with those reported by Ceotto & Di Candilo (), the annual SOC increment under black locust was double in this study site (120 g C m −2 yr −1 ) compared to that previously observed (58 g C m −2 yr −1 ).…”

“…() compared SOC stock variations under poplar and switchgrass in relation to those in a nearby arable field and did not find differences between these species. Also Ceotto & Di Candilo () did not report significant differences between herbaceous and woody crops. The results presented in this study are in agreement with those reported by Bonin & Lal (), in which lower SOC stock increments were found in switchgrass compared to willow.…”

“…The increase in SOC under giant reed progressed at a relatively slow rate (54 g C m −2 yr −1 ) compared to what reported in other studies in Italy (Riffaldi et al ., ; Ceotto & Di Candilo, ). These contrasting results could be a consequence of the lack of nitrogen (N) fertilization in this study and the higher below‐ground biomass production reported by other authors (Monti & Zatta, ).…”

Comparative attributional life cycle assessment of annual and perennial lignocellulosic feedstocks production under Mediterranean climate for biorefinery framework

“…This estimate is in line with the average annual soil carbon storage that Arrouays et al () highlighted for land conversion from arable to grassland (0.5 ± 0.25 ton ha −1 over a 20‐year period). The C sequestration rate appeared consistently lower compared to available estimates from literature, ranging from 1.00 ton organic‐C ha −1 yr −1 (Sarkhot et al ) to 1.70 ton organic‐C ha −1 yr −1 (Ceotto and Di Candilo ). Such amounts would have led to very different results if implemented in the present analyses (also to a net sink, in the latter instance).…”