The Impact of Soil Water Content on Yield, Composition, Energy, and Water Indicators of the Bioenergy Grass Saccharum spontaneum ssp. aegyptiacum under Three-Growing Seasons

Raising water and energy productivity in agriculture can contribute to reducing the pressureon the limited freshwater availability and non-renewable energy sources. Bioenergy perennial grassesare efficient from a water perspective and can afford a low-energy cultivation system; however, cropselection and cultivation practices for minimizing land use change and maximizing resource useefficiencies remain a challenging task in view of sustainable bioeconomy development. The presentwork investigated the soil water effect on a long-term plantation of Saccharum (Saccharum spontaneumssp. aegyptiacum), a bioenergy perennial grass holding great promise for semiarid Mediterraneanareas. The plantation was in its 13th year following establishment and was subjected to three levels ofirrigation for three successive growing seasons. Regression models between crop water use (CWU)and productivity, biomass composition, energy, and water indicators showed different predictioncurves. Raising CWU (from 230 to 920 mm) enhanced the dry biomass yield (from 14.8 to 30.1 Mgha-1) and the net energy value (from 257.6 to 511 GJ ha-1). On the same CWU range, unirrigatedcrops improved the energy efficiency (from 99.8 to 58.5 GJ ha-1), the energy productivity (from 5.6to 3.4 Mg GJ-1) and the water productivity (from 114.5 to 56.1 MJ m-3) by reducing the waterfootprint (from 8.7 to 17.8 m3 GJ-1). Biomass composition was also superior in unirrigated crops,as the lower heating value, structural polysaccharides, and the acid detergent lignin were higher,while ash and soluble compounds were lower. Present findings demonstrated the good yield levelsand persistence of Saccharum, improving our knowledge of plant responses to changing soil wateravailability to maximize energy and conserve natural resources, paving the way for sustainablebioeconomy development in the Mediterranean area.