Ensuring energy profitability and environmental sustainability through assessing marginal land suitability in China

Growing lignocellulosic feedstock on marginal land is one of the attractive ways to achieve China's goals of sustainable development and carbon neutrality while transforming its energy structure. The expansive use of nationally distributed and heterogeneous marginal lands is prone to widespread concerns about sustainability risks at all stages. We utilised a productivity-based suitability index to classify marginal land and examined net energy value (NEV) and greenhouse gas (GHG) emissions under various marginal land development scenarios through extending system boundary from input of field production to energy consumption. We found that marginal lands with high suitability are concentrated in the Northeast, East, and Central China, while marginal lands in the Northwest and Southwest are generally unsuitable for bioenergy crops. The seed and chemical inputs in agricultural production and the enzyme and electricity consumption in ethanol production account for 79∼89% of the total energy inputs, while GHG emissions are dominated by the nitrogen fertilizers to marginal land and electricity consumption in ethanol production. Half of the NEV and reduction in GHG emissions can be obtained by only developing high suitability marginal area, which account for 25% and 14% of the total available marginal land under low and high input scenarios. Whereas, low-yielding fields concentrated in the Southwest can bring serious negative environmental returns. Assessing the suitability of marginal land can help identify promising pathways for ensuring sustainable development.