POPULATION-DYNAMICS OF RUMEX OBTUSIFOLIUS UNDER CONTRASTING LUCERNE CROPPING SYSTEMS

The population dynamics of Rumex obtusifolius L. was analysed in a luc erne:winter cereal crop rotation by means of a matrix population model that takes into consideration two crop rotation periods: the lucerne (Medicago sativa L.) cropping period and the cereal cropping period. S everal transition matrices based on life-cycle stages were calculated for each cropping period using experimental data and were used in the construction of a model that analyses the population dynamics of R. ob tusifolius under different harvest dates and lengths of lucerne croppi ng periods. Model projections showed that populations of R. obtusifoli us increased during the lucerne cropping period regardless of harvest date and decreased during the cereal cropping period. Under a late har vest date, populations decreased at each crop rotation when lucerne wa s grown for 3 years, remained close to the equilibrium when lucerne wa s left to grow for 5 years, and increased for longer lucerne cropping periods. In contrast, populations of R. obtusifolius decreased even wi th a lucerne cropping period of 9 years under an early harvest date. T he significance of these results in relation to the biology and the no n-chemical control of the species is discussed.