| Abstract: | Our objective was to survey the phosphorus (P), potassium (K), pH, calcium (Ca), magnesium (Mg), and organic-matter (OM) levels of soils in Illinois, including the degree of nutrient vertical stratification. Soil samples were collected from depths of 0–8 and 8–18 cm in 547 randomly chosen fields throughout Illinois and analyzed for nutrients, pH, and OM. Forty-six percent of samples were below the critical range for K (130 to 150 mg K kg?1), and 59% of samples were above the soil P levels, requiring no additional fertilization. Soil pH ranged from 4.7 to 8.1. Mean Ca and Mg levels were nonlimiting for crop production, and OM was correlated (R2 = 0.690) with corn grain yield. Vertical stratification (surface/subsurface ratio) was 2.4:1 for P and 1.5:1 for K. Many fields with greater than needed P levels and less than suggested levels for K present opportunities for improvement in fertilizer management. |
