Nitrogen fertilisation and harvest time on biomass production and composition of tall wheatgrass in Mediterranean marginal conditions

Abstract

Among several cool-season grasses, tall wheatgrass (Elymus elongatus (Host) Runemark) has been recently identified as a promising energy crop for Mediterranean low productive areas under rainfed conditions. The influence of annual N top dressing applications (0, 30, and 80 kg ha−1) on the production, composition and combustion quality properties of tall wheatgrass biomass was studied for 9 years on marginal land. The effect of harvest time was evaluated from early summer until late winter with three cultivars of tall wheatgrass (‘Alkar', ‘Jose', and ‘Riparianslopes').

Biomass production grew with increasing N input and spring rainfall. The 80 kg N ha−1 treatment provided mean dry matter production of 4.1 Mg ha−1 yr−1 but elevated biomass N levels from 8.5 to 10.0 g kg−1. An autumn harvest in mid-October led to dry matter losses of 16%, and reduced moisture (−48%), ash (−24%), N (−39%), Cl (−61%), S (−24%) and ash K2O (−41%) levels. Delaying harvest time until late winter greatly improved fuel quality, reducing N by 51%, and Cl and K by 80–85%, while increasing deformation and flow temperatures by 370 °C and 240 °C, respectively, but led to matter losses of 36–48%. The differences found in the chemical composition of tall wheatgrass across years and N applications up to 80 kg N ha−1 yr−1 are not expected to be of any practical relevance if this type of biomass is utilised in combustion processes. On the contrary, a harvest delay can improve quality properties for combustion.