Abstract
Sorghum bicolor (L.) Moench, called sweet sorghum, is a drought-resistant and heat-tolerant plant used for ethanol bioenergy production, and is able to reduce the competition between growing crops for energy vs. growing crops for food. Quantitatively mapping the marginal lands of sweet sorghum is essential for the development of sorghum-based fuel ethanol production. However, knowledge of the contemporary marginal lands of sweet sorghum remains incomplete, and usually relies on sample data or is evaluated at a national or regional scale based on established rules. In this study, a novel method was demonstrated for mapping the global marginal lands of sweet sorghum based on a machine learning model. The total amount of global marginal lands suitable for sweet sorghum is 4802.21 million hectares. The model was applied to training and validation samples, and achieved high predictive performance, with the area under the receiver operating characteristic (ROC) curve (AUC) values of 0.984 and 0.978, respectively. In addition, the results illustrate that maximum annual temperature contributes more than do other variables to the predicted distribution of sweet sorghum and has a contribution rate of 40.2%.
Highlights
Fossil fuels are non-renewable energy resources that continue to be consumed as a driver of social and economic development
To make an accurate map of the marginal lands of sweet sorghum, the boosted regression trees (BRTs) model required three types of data sets: (a) a set of of the marginal lands of sweet sorghum, the BRT model required three types of data sets: (a) a set of high-spatial-resolution global environmental variables affecting the growth of bioenergy plants such high-spatial-resolution global environmental variables affecting the growth of bioenergy plants such as sweet sorghum; (b) a global georeferenced dataset for known sweet sorghum areas; and (c) a set as sweet sorghum; (b) a global georeferenced dataset for known sweet sorghum areas; and (c) a set of absence points that define unsuitable environment conditions for sweet sorghum
India is suitable for sweet sorghum, but only a small amount of land can be used to grow the bioenergy plant because most of the land is needed for food production
Summary
Fossil fuels are non-renewable energy resources that continue to be consumed as a driver of social and economic development. This consumption depletes fossil fuel reserves and leads to the intensification of global climate change [1]. The main strategies to reduce global greenhouse gas emissions measures include reducing energy demands, improving energy efficiency, and developing renewable energy [4,5,6]. Based on Europe’s 2009 Renewable Energy Directive, each member state needs to supply 10% of transport energy from renewable sources—a proportion of which will come from biofuels by 2020 [7].
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