Competition between maize and Datura stramonium in an irrigated field under semi-arid conditions

Crop growth of maize (Zea mays L.) and Datura stramonium L. in monoculture and competition was studied over 4 years in a flood irrigated field in Zara goza (Spain). Plant density was 8.33 m(-2) for maize and 16.66 m(-2) (1994 and 1995) and 8.33 m(-2) (1996 and 1997) for D. stramonium. Maize yield was decreased by 14-63% when competing with the weed. Yield reduction increase d as the time between crop and weed emergence decreased. The development of leaf area per plant during the exponential growth phase was faster in maiz e primarily because the leaf area of maize seedlings at emergence time was greater than that of the weed. The faster growth of maize in leaf area and height reduced the photosynthetically active radiation received by the weed . Datura stramonium had a lower radiation use efficiency (RUE) than maize. Competition from the weed slightly decreased the maximum leaf area index (L AI) of the crop, and leaf senescence of maize was accelerated. The weed com peted with the crop late in the season reducing crop growth rate, grain num ber per ear and grain weight. Competitive ability of D. stramonium for ligh t was mainly due to its growth habit, with the leaves concentrated in the u pper part of the canopy (more than 75% of LAI in the upper 25% of its heigh t), its higher light extinction coefficient (0.89) and its indeterminate gr owth habit. The N plant content of maize was not influenced by the presence of the weed. The weed had a higher N plant content than the crop throughou t the season and took up more N in monoculture.