Effects of soil water content and nitrogen supply on the productivity of Miscanthus x giganteus Greef et Deu. in a Mediterranean environment

Miscanthus x giganteus is one of the most promising biomass crops for non-food utilisation. Taking into account its area of origin (Far East), its temperature and rainfall requirements are not well satisfied in Mediterranean climate. For this purpose, a research was carried out with the aim of studying the adaptation of the species to the Mediterranean environment, and at analysing its ecophysiological and productive response to different soil water and nitrogen conditions. A split plot experimental design with three levels of irrigation (I1, I2 and I3 at 25%, 50% and 100% of maximum evapotranspiration (ETm), respectively) and three levels of nitrogen fertilisation (0 kg ha-1: N0, 60 kg ha-1: N1 and 120 kg ha-1: N2 of nitrogen) were studied. The crop showed a high yield potential under well-watered conditions (up to 27 t ha-1 of dry matter). M. x giganteus, in Mediterranean environment showed a high yield potential even in very limited water availability conditions (more than 14 t ha-1 with a 25% ETm restoration). A responsiveness to nitrogen supply, with great yield increases when water was not limiting, was exhibited. Water use efficiency (WUE) achieved the highest values in limited soil water availability (between 4.51 and 4.83 g l-1), whilst in non-limiting water conditions it decreased down to 2.56 and 3.49 g l-1 (in the second and third year of experiment, respectively). Nitrogen use efficiency (NUE) decreased with the increase of water distributed (from 190.5 g g-1 of I0 to 173.2 g g-1 of I2); in relation to N fertilisation it did not change between the N fertilised treatments (N1 and N2), being much higher in the unfertilised control (177.1 g g-1). Radiation use efficiency (NUE) progressively declined with the reduction of the N fertiliser level (1.05, 0.96 and 0.86 g d.m. MJ-1, in 1994, and 0.92, 0.91 and 0.69 g d.m. MJ-1, in 1995, for N2, N1 and N0, respectively).