Pea-barley intercropping for the control of weeds in European organic cropping systems

Two pea-barley intercropping strategies were compared with respective sole crops for their capacity to reduce weeds. Crops were grown under organic conditions without mechanical weeding. Field trials were carried out during three years throughout Europe. Although crops were tested under diverse soil and climate conditions, in the presence of different weed species and varying weed biomass, it appeared in all experimental sites that weeds were better controlled in barley sole crop or in intercrops than in pea sole crop. Differences in the degree of weed control between crop treatments were already visible at flowering and sometimes increased until maturity. It is interesting to note that the substitutive and additive designs obtained similar results. The higher plant population density in the latter did not enhance competitive ability against weeds. This study also highlighted the importance of soil N in crop competition with weeds. The presence of barley in the intercrops, which increased the accumulation of N from soil compared to pea sole crop, consequently reduced weed levels.