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Seasonal Variability of pH and Lime Requirements in Several Southern Michigan Soils When Measured in Different Ways¹

ABSTRACT

The seasonal variability of pH and lime requirement of the plow layer of 13 soil series, at 19 sites, by various methods on field-moist, air-dry and oven-dry samples were observed from May through September 1966 near East Lansing, Mich. Several factors associated with variation in pH were also observed.

At the beginning of the season, the mean glass electrode-pH of air-dry and oven-dry samples measured in each of three suspending media—water, 1.0N KCl, and 0.01M CaCl₂—were each significantly lower than the corresponding field-moist pH. On air-dry samples, pH measurements with the glass electrode in water are significantly correlated with those in 0.01M CaCl₂ (r = 0.96) and in 1.0N KCl (r = 0.92) or those measured with the Truog kit (r = 0.90).

The pH of field-moist samples in water showed a maximum seasonal variability of 1.6 pH units and an average variation of 0.8 pH unit. The pH of samples in 1.0N KCl showed the least average seasonal variability of the methods used, 0.2 pH units. Electrical conductivity gave the highest correlation (r = -.82) with seasonal variability of pH on air-dry samples in water. The glass electrode pH on air-dry samples in 1.0N KCl were better correlated (r = .63) with percentage base saturation than those in water (r = .53) and slightly better than those in 0.01M CaCl₂ (r = .61).

Four of 11 sites studied had a lime requirement early in the season but each of the 11 sites had a lime requirement in midsummer.

¹ Michigan Agr. Exp. Sta. Journal Article no. 4630.

² Graduate Assistant, and Professor of Soil Science; Assistant Professor of Crop Science, Michigan State University, respectively.

Received for publication June 19, 1969. Accepted for publication August 12, 1969.