Rainfall effects on grass-weed seedbanks in wheat

Abstract

Forage, chickpea, medics, wheat, oilseed rape and sunflower were cultivated during four years as part of ten different types of rotations which always included wheat . These experiments took place in Southern Portugal, a mediterranean area where dryland agriculture is usual. Grass-weed seedbanks were evaluated annually before seeding. The variation in wheat plots without weed control was used to assess the effects of rainfall on grass-weed seedbanks. Evaluation of all grass-weeds taken together was made, and of each of the three major contributors, namely Agrostis pourretii Willd., Phalaris minor Retz. and Briza maxima L.. In mediterranean dryland agriculture, where water is a very limiting factor, rainfall appears to have a very strong and rapid effect on grass-weed seedbanks. In fact, the amount of rain felt between November and April has a direct effect on grass-weed seedbank density after the crop regarding all grass-weeds, Phalaris minor and Briza maxima. Conversely, Agrostis pourretii seedbank grows independently of rainfall until its own seed density becomes a limiting factor.