Application of allelopathic plants for the control of weeds in many crops has been proved. This field study was conducted for two years (2001-2002) at Hamadan agricultural research center. Experiments were a factorial design based on randomized complete block with 8 treatments and 4 replications. Three crops (Brassica napus, Vicea sativa, Secal cereal) as allelopathical crops were cultivated by alone, double and treble at autumn season and as green manure, mixed with soil at spring, and then a week after, potato (Agria) was planted in plots. Results showed that, there were significant differences in all measured parameters include of fresh weight of cover crops (g/m2 ), fresh weight of weeds (g/m2), number of weeds per square meter and potato yield (t/ha). S. cereal treatment has the highest fresh weight between cover crops. All of treatments could reduce number and weight in weeds at comparison with check treatments (without cover crop). Yield of potato increased by 40% in top treatment (S. cereal) in comparison with check treat.
The final results revealed that, the allelophathical plants as cover crops, before potato, not only increases yield, but also decrease weed population in potato field without usage of herbicides.