Crop and Weed Growth in a Sequence of Spring Barley and Winter Wheat Crops Established Together from a Spring Sowing (Relay Cropping)

A relay cropping system of cereals, whereby winter wheat (Triticum aestivum L.) was undersown in two-row spring barley (Hordeum distichum L.), was established in a field trial in central Sweden in 1999 and continued until 2000. The purpose of the study was to examine crop and weed responses to different plant densities of the undersown winter crop. Winter wheat was sown at four seed rates (187, 94, 47 and 0 kg ha -1 ) immediately after the sowing of barley. Barley was harvested in the first autumn after sowing and winter wheat in the second autumn. The grain yield of barley was not affected by the seed rate of wheat, and averaged 4580 kg ha -1 . Winter wheat did not vernalize during the first growing season but remained at the vegetative stage. The grain yield of wheat was 1990 kg ha -1 for the lowest and 5610 kg ha -1 for the highest seed rate of wheat. Whilst the undersowing process itself stimulated weed emergence in this experiment, increasing the undersowing seed rate reduced the population of perennial weeds by 40-70 %. In the second growing season, the total biomass of weeds was 66 % higher at the highest seed rate compared with the lowest seed rate.