NITROGEN-FERTILIZATION OF BARLEY UNDER SEMIARID RAIN-FED CONDITIONS

Two barley cultivars (Hordeum vulgare L.) were grown at a site in semi -arid northeast Spain during three seasons, 1986-87, 1987-88, 1988-89, under two levels of N-fertilization (100 kg ha(-1), the normal dressi ng used in the area, and 50 kg ha(-1)). There was no benefit for yield from the higher rate of N fertilization; in 1987, a very dry season, the higher rate depressed yield. Nitrogen fertilization increased gree n area index and nitrogen uptake by the plant but did not affect any y ield component. Harvest index was negatively affected by nitrogen in t he driest year. The responses to nitrogen differed with cultivars. Rai nfall amount and distribution of the year and probably the residual ni trogen in the soil strongly influenced the response to N-fertilization . It is concluded that less nitrogen fertilizer than at present used m ay improve the sustainability and stability of the cropping system wit hout reducing the grain production in this area.