Since this paper was completed, Reith & Inkson (1958) have presented results for a further series of factorial experiments with f.y.m. and fertilizers in north-east Scotland, 1947–54. The authors claimed that for N their results confirmed those of Crowther & Yates; however, their Table 3 gives results very similar to those presented here: i.e. in the absence of f.y.m., PK basal greatly increased the response to N, but was ineffective where f.y.m. was also applied. The authors appear to have appreciated that these results, based on individual plot yields, were inconsistent with their main conclusions drawn from main effects and first-order interactions only, but do not seem to have realized their significance.