PRODIVA, Crop species mixtures for weed suppression: Deliverability No. D2.3 Technical report

The aim of the studies performed in PRODIVA working package 2 was to assess the weed suppressive ability of crop mixtures (spring barley + peas) compared to ability of pure crops to suppress weeds. The work was done by means of field trials in which natural weed populations were used while controlled experiments were used with Elytrigia repens or Sinapis alba as a model weeds. Over a period of three years, 5 field experiments and 9 experiments under controlled conditions were performed in Poland and Sweden. In all experiments, performance was assessed in terms of the crops ability to compete against weeds (AC). The ability to withstand competition from weeds (AWC) and the relative weed biomass in the intercrop, compared to weed biomass in the sole crops (RWB) was also calculated if data were available. In some of the experiments, a treatment with only weeds was added as a control to assess the effects of crop presence on weeds. In some of the experiments, the leaf area index was measured over time, hypothesizing that LAI and leaf area duration (LAD) would be explanatory traits of importance for weed suppression. The overall results confirm that sole pea is a weak competitor in comparison to spring barley and that an intercrop of pea and spring barley may have a strong weed suppression. However, the results obtained in this study varied from year to year and from site to site. The performance of an intercrop is difficult to predict in advance and seems to depend on factors such as precipitation, nutrient availability, proportion of intercrop components and actual weed species composition, which all interact. A good crop establishment is essential for weed suppression under all circumstances. The weed suppressive effect of an intercrop is at least for a large part due to shading, and one of elements which may contribute to the weed suppressive ability of an intercrop is capacity to maintain a leaf area over a longer period than the sole crop components.