So far, we have seen the results of Lange (2011), who suggests that the use of degraded lands is likely to have beneficial GHG reduction effects. But in science nothing can definitely be considered to be correct or incorrect, until proven wrong (Castree et al., 2005); so do other studies come to the same conclusions?
To be able to answer this question, the definition of ‘degraded land’ must be compiled. Nair et al. (2011) suggest that this comprises of lands not currently utilized for anthropogenic activities with decreased biodiversity and primary productivity, which often occur due to anthropogenic activities such as overgrazing, poor agricultural management and deforestation. Such conditions, if management is not improved, may lead to detrimental knock-on effects on the environment, such as soil erosion. This means that if managed well, converting to biofuel production may immediately result in an environmental benefit before the GHG emissions are considered; but what about the GHG emissions?
Using this definition, Nair et al. (2011) have found that converting degraded grassland to biofuel crop production, including the often bedevilled oil palm, produces little extra GHG emissions (including carbon dioxide, nitrous oxide and methane), which only tend to be short-term. This means that these emissions will be compensated for in the long-term, resulting in a net GHG saving over time. However, there are some exceptions, where in the case of degraded tropical rainforest conversion, the extra emissions tend to be of unsustainable levels. Additionally, the biofuel crop type matters, with the nitrogen-demanding corn, sugarcane and soybean being unsuitable for growing on degraded lands, as they will require vast amounts of synthetic nitrogen fertilizer, increasing GHG emissions, as explained in previous posts. Non-nitrogen intensive crops, such as jatropha and oil palm, however, are ideal without major addition of fertilizer despite the low soil fertility, thus resulting in net GHG saving.
However, there are a number of problems with the results of the study. Firstly, there is an issue with defining ‘degraded land’. There is no single agreed definition of the term, meaning that previous definitions differed among each other, which would result in highly varied GHG effects calculations of ‘degraded land’ conversion. For example, Dregne and Chou (1994) suggested that degraded lands comprise 3.6 billion ha in arid regions, while Oldeman (1994) calculated this to be 1.9 billion ha globally (Nair et al., 2011). This great variation means that care should be taken to remember that the results of Nair et al. (2011) only apply to their definition of ‘degraded land’. Secondly, it is important to remember that the results of this study describe the GHG emissions from ‘degraded lands’ conversion overall and it is therefore important not to generalise, as spatial and temporal variations exist in soil characteristics, climate and management practices. Thirdly, the authors mention the presence of data gaps on GHG fluxes in areas such as the tropics, making the results less representative of spatial and temporal variations in emissions. Additionally, it is important to remember the ubiquitous problem of uncertainty in some factors, such as the major uncertainty in nitrous oxide emissions (Nair et al., 2011).
In conclusion, although there are some uncertainties, as there are with every model (Castree et al., 2005), conversion of degraded lands to biofuel cultivation is likely to generally have a positive impact on GHG emissions, provided Nair et al.’s (2011) definition of degraded lands is used. However, site-specific evaluations of the precise outcome may be useful. Nonetheless, the results of the study suggesting a promising future for biofuels cultivation on degraded lands in terms of GHG emissions agree with the results of Lange (2011). This is good news, as degraded lands provide a source of land for biofuel cultivation of which there is a shortage at the moment, supposedly without major environmental and socio-economic problems, such as putting pressure on biodiversity and food production. Additionally, under good management biofuels may reduce problems that degraded lands often entail, such as soil erosion, producing further benefit.
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