Research is needed to further evaluate N by K interactions in crops. The objective of this study was to evaluate potential interactions in corn (Zea mays L.). Two long-term trials with continuous corn were evaluated from 2013 to 2017 in two Iowa soils. Annual treatments were the combinations of five N rates (0-336 kg N ha-1) and four K rates (0-66 kg K ha-1) replicated three times. Grain yield, ear-leaf (R1 stage) and grain (at harvest) N and K concentrations, N and K removed with grain harvest, and post-harvest soil-test K (STK) (15-cm depth) were measured each year. Leaf N concentrations were not affected (P ≤ 0.05) by K fertilization at either site, were increased by all N rates, and there was no N by K interaction. Leaf K concentration was increased by K, was slightly affected by N, and a significant N by K interaction indicated that N decreased leaf K without K at one site but increased leaf K with the highest K rate at the other site. Grain N concentration was increased by N at both sites, was increased by K at one site, and there was no interaction. Grain K concentration was decreased by N, was increased by K, and an interaction at one site indicated that K fertilization partially alleviated the N decreasing effect. Nitrogen and K fertilization increased grain yield, N and K removed, and significant interactions indicated that with adequate K supply the responses to N were higher and a higher N rate was needed to maximize yield compared with low K supply. The higher K removed with the higher N and K rates sharply decreased STK over time. The study demonstrated that a K deficiency limits corn yield and also limits its capacity to respond to N fertilization.

Abbreviations: Analysis of variance, ANOVA; Completely randomized design, CRD; Randomized complete block design, RCBD; Soil-test K, STK.