Illinois Fertilizer
Conference Proceedings
January 24-26, 1994
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Twice Monthly Field Soil Sampling For Soil Testing
To Evaluate Reproducibility Of Soil Test Levels
Ted R. Peck and Marilyn E. Sullivan1
Two previous monthly field soil sampling studies have been done in Illinois. The
results indicated relatively stable pH and phosphorus soil test levels on soil
samples collected from the field during all months of the year. However the potassium
soil test showed a cyclic nature with low K soil test levels mid-late summer (August)
relatively high K soil test levels in mid-winter (February) and K soil test levels
somewhere between during the rest of the year. While the cyclic nature of K soil
tests was consistent, the K soil test levels from year to year were inconsistent
in reflecting a higher or lower soil K fertility level relative to established
acceptable critical levels. While there is some understanding of the causes of
K soil test fluctuation, manipulating the soil sample and predicting the soil
K test level have been met with little success. The objective of this study is
to sample, twice monthly, field plots with different histories of potassium and
phosphorus fertilization applications for a period of years to better characterize
the reproducibility of soil test levels over time to improve the prediction of
soil tests.
Footnotes and References
1Ted R. Peck is Professor and Marilyn E. Sullivan is Research Specialist,
Dept. of Agronomy, Univ. of IL.
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