Soil Fertility Status of Soils in Illinois

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.