Water and nitrogen balance of sweet sorghum (Sorghum bicolor moench (L.)) cv. Keller under semi-arid conditions

► It is possible to obtain high yield production in semiarid Mediterranean environment. ► Yield of sweet sorghum was affected by the water availability but not by nitrogen supplied. ► The nitrogen dilution curves allow to manage nitrogen fertilization in relation to water availability. ► In Mediterranean environment cultivating sweet sorghum to produce bioethanol biofuels allows to obtain positive nitrogen budget in the soil. In the framework of the E.U. project Fair CT 96-1913 “Environmental studies on sweet and fibre sorghum, sustainable crops for biomass and energy”, a research has been carried out with the aim to study the water and nitrogen balance and determine the critical N dilution curve of sweet sorghum cv. Keller. A field experiment was performed, where three irrigation treatments (I0=dry control, I50=50% ETm restoration, I100=100% ETm restoration) and four nitrogen fertilization levels (N0=no nitrogen control, N60=60kgha−1, N120=120kgha−1; N180=180kgha−1) were studied. The final yield was significantly affected by the amount of water distributed but not by the nitrogen level. The treatments watered up to crop establishment (I0) produced, in the average, 7.5tha−1 of dry matter, against 21.1 and 27.1tha−1 of I50 and I100, respectively. The crop determined a great reduction in nitrate concentration of soil water, irrespective of nitrogen supplied. The variation between N output and input (Δ) was negative in N0, N60 and N120 and positive in N180. The critical value of nitrogen uptake change in relation to the water availability. The amount of nitrogen supplied did not determine significant differences upon WUE. The crop seems to have a great potentiality in Mediterranean environment in terms of yield production.