Inoculated soybeans (Glycine maxL. Merr. cv. Eragg) were grown in an intensively managed cabbage (Brassica oleraceaL. Capitata group)‐ sweetcorn (Zea maysL.) multiple‐cropping sequence on a tile‐drained Arenic Haplaquod having variable residual K levels. The study was conducted to assess the effect of residual and applied K on soybean K and N composition, nodulation, root growth, and pod formation. Sidedress treatments of 0 and 100 kg K/ha were applied at bloom to plots that received either 0 or 300 kg K/ha/acre that had been applied previously to other crops in the sequence. Treatments were arranged in a randomized complete block design witn six replications. Although leaf N conc, was uniform at bloom (R2), leaf N at pod‐fill (R6) ranged from 2.8 to 4.3% and wasquadratically related to leaf K (r2= 0.92). Without residual K fertilizer from cabbage and sweet corn applications sidedress application of K increased leaf and nodule K and N. Root K conc. was correlated with root dry wt. (r = 0.35) at bloom stage, and with root 10 dry wt. (r = 0.54), pod number (r = 0.43), and pod dry wt. (r = 0.39) at pod‐fill stage. Root K conc. was negatively correlated with nodule number (r = ‐0.34) and nodule dry wt. (r = ‐0.41). Sidedress‐applied K did not increase root growth and pod number whereas residual fertilizer K did. A curvilinear relationship between leaf K and N conc. and a linear relationship between leaf N and soybean yield indicated that K deficiency limited the capacity of the soybean plant to supply N to the developing grain during pod‐fill, and that this response was not due to inadequate nodulation.