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)) was similar to C (11.3 Mg d.m. ha(-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.