Nitrogen fertilizer can increase dry matter, grain production and radiation and water use efficiencies for durum wheat under semi-arid conditions

Responses of durum wheat (Triticum durum, cultivar Karim) to application of nitrogen fertilizer and irrigation have been analysed in the semi-arid areas of Tunisia. The aim is to establish the value, for crop production, of applying N fertilizer under non-irrigated conditions and analyse the mechanisms of responses in two soil types: a clay soil at Cherfech and a sandy soil at Nabeul. Irrigation increased above-ground dry matter production substantially on the sandy soil but not on the clay soil. Nitrogen application also stimulated dry matter production substantially in nonirrigated (rainfed) as well as irrigated conditions. The stimulation was greater under drought conditions than well-watered conditions: 37% compared to 27%, respectively. Positive effects of N were obtained on both soils over all years. The effect was due to increased LAI, and maintenance of green crop duration. This increased total dry matter, which resulted in improved efficiencies of radiation and water use. However, the nitrogen use efficiency decreased with nitrogen application. The mechanisms of the effects and the impact on durum wheat production and its improvement under semi-arid conditions are considered. (C) 1998 Elsevier Science B.V.