Influence of soil moisture on the competitive ability and seed dormancy ofSinapis arvensis in spring wheat

Two experiments were carried out, one in 1995 and one in 1997, to investiga te the competitive abilities of two spring wheat cultivars with Sinapis arv ensis L. The spring wheat cultivars (Baldus and Canon) of contrasting growt h habit were grown with and without S. arvensis under two different moistur e regimes (10% and 70% of field capacity). In 1995, S. arvensis was found t o be less competitive when subjected to moisture stress, resulting in small er wheat yield losses in dry soil than in moist soil. In both years, seed p roduction of S. arvensis was reduced by competition and moisture stress, an d the seeds produced by plants that had been grown in drier soil were small and had negligible dormancy. Hence, in dry conditions, the competitiveness of S. arvensis and its potential to produce persistent seed may be reduced . Some differences between the two wheat cultivars were evident: cv. Baldus was more competitive against S. arvensis than cv. Canon. This could be att ributed to differences in carmopy structure.