Data sets used for analyses made in the article Temporal and spatial positioning of service crops in cereals affects yield and weed control collected under three field seasons in four experiments studying a relay intercropping system of cereals and forage legumes. For more details on the experiment see the article. The treatment and experimental names were changed for the article: Experimental sites: SK1 = 3583 OG1 = 3584 SK2 = 3585 OG2 = 3586 Treatments: Early Intra = A Late Inter = B Late adjacent = C Control (no service crop) = 1 Frost sensitive annuals = 2 Perennials = 4 Frost tolerant annuals = 3 For the proportion of fixed nitrogen (files starting with N15leg) two different questions (Q1 and Q2) were asked to the data set, according to the data included. .1 and .2 indicate that the data sets are from all experiments or only experiments where frost tolerant annuals were included. Q1 = Does the proportion of fixed nitrogen in SC above ground biomass vary between service crop species? Q2 = Does the proportion of fixed nitrogen in SC above ground biomass vary between SC sowing time? WA is an abbreviation which was earlier used for frost tolerant annuals, so the same as the abbreviation T in the article. Hence, files with the word "all" in the name were used for the analyses called "S & P" in the article. While those with the abbreviation WA or ABC in the name were used for the analyses called "S, P & T" in the article.