---Forage legumes are used to enhance soil fertility of the agroecosystem. Understanding their effect on the agroecosystem during their growing period is essential. The objective of this field study was to evaluate annual clovers intercropping and earthworm activity on the growth of weeds. The field experiment was carried out during the 2006–2007 growing seasons at the research farm of the Seed and Plant Improvement Institute, Karaj (Iran) involving various mixed cropping ratios of berseem clover (Trifolium alexandrinum L., B) and Persian clover (Trifolium resupinatum L., P) (B : P = 1 : 0, 3 : 1, 1 : 1, 1 : 3) with and without earthworm Pheretima sp. inoculation. Nitrogen content of plants and weeds as well as biomass was measured. Forage yield was higher in 2006 than 2007 but had similar response to cropping systems and earthworm inoculation. Total forage yield was highest in mixed cropping system (MCS). While in the first cut, the berseem sole crop (SC) tended to greatly suppress the growth of weeds, in the second cut Persian clover sole crop further suppressed weeds. The greater total crop biomass had an even higher weed suppression. Earthworm activity did not affect cut 1 but increased forage and weed biomass yield in cut 2. However in cut 1, berseem tended to greatly suppress the growth of weeds, which may be explained by the greater nitrogen accumulation in monocultures and intercrops, Persian clover in cut 2 had greater suppression on weed biomass production. Nitrogen accumulation of crops and weed increased under earthworm activity in the second cut.
