Relay-cropping enhances the availability of low iLUC risk lignocellulosic feedstock for advanced biofuels

The relay-cropping (R) of a winter cereal and a high biomass yielding legume for advanced biofuel production can enlarge the legume growing season, thus increase its biomass yield and synchronize nitrogen (N₂)-fixation capacity to uptake. The aim of the present study was to evaluate the biomass and food yield of two sunn hemp (Crotalaria juncea L.; cv. Ecofix) – wheat (Triticum aestivum L.; cv. Bologna) relay-cropping systems compared to double-cropping, in order to explore the impact on grain and biomass yield of the variable crops overlapping periods. The evaluated relay-cropping systems foreseen an early November wheat sowing into no till bare soil with: i) sunn hemp harvested at full flowering (beginning of November, R1) and ii) sunn hemp harvested at the end of flowering (end of November, R2). In the control (C) double-cropping, sunn hemp was harvested at the beginning of flowering (end of September). Quantitative and qualitative parameters were evaluated for each system across two growing seasons (2019–20 and 2021–22). Sunn hemp biomass and wheat straw residues were determined. The grain qualitative parameters determined for wheat were: grain volume weight (VW), crude protein, wet gluten, starch and Zeleny index (ZI). The R1 and R2 sunn hemp-wheat relay-cropping biomass yield (12.5 Mg d.m. ha⁻¹ y⁻¹) was similar to C (11.3 Mg d.m. ha⁻¹ y⁻¹). In 2019–20, environmental conditions were more favorable, thus, yields were higher than in 2021–22 by 72 %. Wheat grain yields in 2021–22 were higher in R1 (2.9 Mg d.m. ha⁻¹) than C (2.0 Mg d.m. ha⁻¹), with R2 showing intermediate values. In 2019–20, however, the grain quality was higher in R1 than in C for crude protein (+11 %), wet gluten (+15 %), and ZI (+26 %) eventually due to an increased N₂-fixation by sunn hemp that reached full flowering. The local availability of low iLUC risk lignocellulosic feedstock for advanced biofuel could be increased through crop intensification with relay-cropping, showing the potential to provide additional biomass and enhance food quality thus complying with the additionality measures set out by the Delegated Regulation of REDIII.