The number of soil samples tested in soil testing laboratories under the supervision of the College of Agriculture in 1964 showed an increase of 6,028 samples. In 1963, 46,444 samples were tested compared to 52,472 in 1964. These figures do not include the thousands of samples tested in commercial laboratories.
Miller, Harold F., "Soil Test Summary for 1964 Now Available" (1965). Agronomy Notes. 198.