Relationship between N concentration of grain and grain yield in recent winter‐wheat experiments in England and Belgium, some with large yields

Eight winter‐wheat experiments conducted by Rothamsted on clay soils in 1980 and 1981 formed part of an inter‐institute collaborative programme on yield variation. The tests included no N and four amounts of fertiliser N up to 200 kg ha −1 , with and without spray treatments to control pests and diseases. Large grain yields—in excess of 10 t ha −1 —were often obtained, mainly where losses had been limited by sprays. In Belgium, 10 experiments during the same seasons were on a wider range of soils and had spray treatments applied to all plots. Yields exceeding 10 t ha −1 were obtained at one site. Graphs showing the inter‐relationship between grain‐N %, grain yield and N uptake are used to compare the recent results with those from a 20‐year study of similar data from 124 earlier Rothamsted experiments. The envelope curve delineating the range of yield and grain‐N % values from these older experiments enfolded most of the more recent data points, except those deriving from the largest yields which were associated almost entirely with grain‐N % values below the minimum recommended for British breadwheat. The largest grain‐N uptakes were 180–190 kg ha −1 and 170–180 kg ha −1 in the recent Rothamsted and Belgian experiments respectively, compared with 160‐170 kg in the older experiments. The linear or near‐linear relationship between grain‐N % and amounts of fertiliser N, established in the 20‐year study, was again observed in the recent Rothamsted and Belgian experiments, with about 38 kg of added N needed to increase grain‐N concentrations by 0.1%.