SPATIAL VARIABILITY OF PLANT ANALYSIS CALCIUM AND MAGNESIUM LEVELS BEFORE AND AFTER LIMING

Plant samples were taken in an 82.5 ft grid at an early and late sampl ing date in both 1991 and 1992 from a forty acre field in Illinois. Ca lcium (Ca) and magnesium (Mg) were analyzed on each sample and maps we re made showing the levels of each nutrient within the field. Soil pH measurements were also made from each of the same sampling locations f ollowing each year of plant sampling. In the fall of 1991, a calcitic lime application was made using soil pH informations from the 1991 soi l sampling to determine the boundaries and rate of the application. Ca lcium and Mg levels in 1991 roughly defined the area of low pH, except for the early sampled Mg levels. However, low Ca and Mg levels did no t always indicate low pH levels. High Ca and Mg levels did not always indicate high pH levels. Following liming, plant Ca levels correlated better with soil pH and represented areas of high and low pH better th an plant Mg. Other factors which influenced Ca and Mg levels may have been high levels of competitive cations, disease injured plants, and s ubsoil pH not described by surface pH measurement.