Effects of Potassium and Magnesium Applied for Corn Grown on an Irrigated Sandy Soil

While the sandy soils of the Nebraska Sandhills and bordering areas are inherently low in N, P, and S, the levels of K and Mg in many soils are considered to be marginal. This study was conducted to evaluate the effects of repeated application of K and Mg on: (i) grain yield of corn, (ii) concentration of K and Mg in plant tissue, and (iii) soil test values for K and Mg. This study was conducted in north-central Nebraska from 1979 through 1982 at a site that was marginal with respect to K and Mg. The soil was classified as a Valentine loamy fine sand (Typic Ustipsamments, mixed, mesic). Twenty treatment combinations from a 9² complete factorial were selected to fit a central composite factorial design and replicated 3 times. Selected rates of K (0, 34, 67, 101, 134, 168, 202, 235, 269 kg ha⁻¹) and Mg (0, 5.6, 11.2, 16.8, 22.4, 28.0, 33.6, 39.2, 44.8 kg ha⁻¹) were broadcast and incorporated before planting. Whole corn plants were collected from each plot when plants were 40- to 60-cm tall and the leaf opposite and below the ear was sampled each year. These tissue samples as well as samples of grain were analyzed for K and Mg. Grain yields were measured each year. The application of both K and Mg had no significant effect on yield throughout the study. Although the concentrations of K and Mg were marginal as indicated by routine soil test procedures, this soil was apparently able to supply adequate K and Mg for corn production. Soil test values for K and Mg increased linearly with the rate applied. A yearly application of 33 kg K ha⁻¹ was satisfactory for maintaining the initial level of soil test K. The K concentration in both whole plant and ear leaf tissue increased linearly with rate of K applied. In general, the K concentrations in the ear leaf tissue were in excess of the published critical level of 19 g kg⁻¹. The Mg concentration in the plant tissue increased linearly with rate of applied Mg but decreased curvilinearly as the rate of K was increased. The Mg levels were substantially higher than published critical levels.