Intercropping grasses and legumes can contribute to the development of advanced biofuels

Abstract

Intercropping-dedicated biomass crops can significantly contribute to the sustainable development of advanced biofuels while improving yield stability. The objective of this study was to quantify the impact of intercropping of the legume sunn hemp (SH; Crotalaria juncea; cv. Ecofix) on the productivity of pearl millet (PM; Pennisetum glaucum; cv. ICMV I707) and biomass sorghum (S; Sorghum bicolor (L.); cv. Triton), with or without nitrogen fertilisation (150 kgNha−1). The intercrops were SxSH and PMxSH. Quantitative and qualitative biomass traits were evaluated for each cropping system. Land equivalent ratio (LER) and species evenness were used to evaluate the performance of the intercrops. Across fertilisation levels, average biomass yields in 2018 and 2019 were: 23 and 19 Mg ha−1 (SxSH), 18 and 17 Mg ha−1 (PMxSH), 21 and 12 Mg ha−1 (PM), 24 and 20 Mg ha−1 (S), and 14 and 13 Mg ha−1 (SH). Overall, LER showed an increase of 22% in PMxSH and 6% in SxSH over the years. Within the intercrops, S showed a larger competitive effect over SH than PM did; species evenness ranged between 0.56 and 0.67 in SxSH and between 0.89 and 0.92 in PMxSH. Moreover, compared to monocropping, intercropping led to improved qualitative feedstock characteristics for bioenergy applications: intercropped PM showed a higher Si/K ratio (+32%), while intercropped SH showed increased cellulose content (+17%) and reduced N (−39%), Mg (−54%), and Na (−15%) contents. Intercropping-dedicated lignocellulosic crops may be feasible alternatives for providing a mixture of dedicated feedstocks with improved sustainability, yield stability, and biomass quality.