Soil pH Variation Within a Soil. I. pH Variation in Soil Pores Observed in a Column-Leaching Method

Abstract

The traditional method for determining soil pH is to measure the pH of mixed soil samples. The resulting measured soil pH as an average is used to represent the unsampled neighborhood. This average cannot really represent the actual soil pH value if spatially dependent heterogeneity of soil properties exists among the samples. The objective of this study was to develop a more complete understanding of soil pH in soil that had been acidified by use of nitrogen fertilizer. The soil samples obtained from the Van Rockel vineyard in Temecula, CA were taken to run a designed column-leaching test from four random test sites with two replicates per site at the depths of 0–30 cm, 30–60 cm, and 60–90 cm. The pH variation in soil pores was observed periodically through several column-leaching tests. When unsieved soil samples in an air-dried state were used to observe the changes in soil pH as shown by a column-leaching procedure, soil pH values during leaching increased gradually with elapsed time in a third or fourth order polynomial functional manner for the first 30 collectors (roughly 90 min) and approached nearly constant values for the last 10 collectors (roughly 30 min). There was a wide pH differential range (0.42–1.73 pH units) in acidified soil in different fractions. The early collection had pH values less than the traditional method and the late collection had pH values greater than the traditional method.