Demography of Lolium rigidum in winter barley crops: analysis of recruitment, survival and reproduction

Demographic studies were conducted with Lolium rigidum Gaud. growing in win ter barley crops at five sites in central and eastern Spain, over a period of 2 or 3 years. Although threefold differences (34-97%) in annual recruitm ent were recorded in the various experiments, most of the values were close to the overall average (67%). Seedling emergence took place in a very shor t period of time after sowing, with 90% emergence generally being reached a fter a thermal time of 242 d degrees C (provided soil moisture was adequate at sowing). Seedling survival was very high (78-95%) in most experiments, with no clear relationship between this parameter and any of the environmen tal variables studied. Survival curves were relatively linear, with plant m ortality increasing gradually throughout the life cycle of the plant. There were 34-fold differences (from 7 to 237 seeds per plant) in the fecunditie s recorded in the various experiments. Variation in fecundity resulted part ly from differences in crop and weed densities and total precipitation rece ived during the growth cycle. The annual rate of population growth was esti mated based on the above-mentioned parameters. The potential for population growth was high (average lambda=6.21), but large differences were obtained for the different sites and years.