“But some soils do contain lime, do they not?”

“Some soils contain limestone,” replied Percy, “and the analysis of such a soil should report the amount of limestone, or calcium carbonate, based upon the actual determination of carbonate carbon or carbon dioxid, which is a true measure of the basic property of the soil, even though the limestone may be somewhat magnesian in character.”

For a set of soil samples.  Percy collected soil from three different strata.  The first sample represented the surface stratum from the top to six and two-third inches; the second sample represented the subsurface stratum from six and two-thirds to twenty inches; and the third sample represented the subsoil from twenty to forty inches, each sample being a composite of about twenty borings.

In collecting these the hole was bored to six and two-third inches and somewhat enlarged by scraping up and down with the auger, all of the soil being put into a numbered bag.  Then, the hole was extended and the subsurface boring removed without touching the surface soil.  This boring to a depth of twenty inches was put into a second bag.  The hole was then enlarged to the twenty-inch depth but the additional soil removed was discarded as a mixture of the surface and subsurface strata.  Finally the hole was extended to the forty-inch depth and the subsoil from one groove of the auger was put into a third bag.  In this manner about an equal quantity of soil was bagged from each stratum; and twenty such borings taken with an auger about one inch in diameter make a sufficient quantity to furnish to the chemist.

“Of course the surface soil is by far the most important,” Percy explained.  “It represents just about the depth of earth that is turned by the plow in good farming on normal soils; and it weighs about two million pounds per acre.  The subsurface stratum extending from six and two-thirds to twenty inches in depth represents the practical limit of subsoiling; and this stratum weighs about four million pounds; while the subsoil stratum weighs about six million pounds, where the soil is normal, such as loam, silt loam, clay loam, or sandy loam.  Pure sand soil weighs about one-fourth more, while pure peat soil weighs only half as much as normal soil.”

“I wish you would tell me,” said Mr. Thornton, “what the fertilizers cost that have been used on that Rothamsted wheat field.”

“The annual application of nitrogen has been one hundred twenty-nine pounds per acre,” said Percy.  “What will it cost?”

“Well, at twenty cents a pound, it would cost $25.80,” was Mr. Thornton’s reply after he had figured a moment.  “But why didn’t they grow clover and get the nitrogen from the air?”

“For two reasons,” replied Percy.  “First, when those classic experiments were begun by Sir John Lawes and Sir Henry Gilbert in 1844, it was not known that clover could secure the free nitrogen from the air; and, second, the experiment was designed to discover for certain whether wheat must be supplied with combined nitrogen, by ascertaining the actual effect upon the yield of wheat of the nitrogen applied.”