"I'd like to know how these amounts compare with what your Illinois soil contains," said Mr. West. "We have several different kinds of soil in Illinois," replied Percy. "The common corn belt prairie soil is called brown silt loam. It contains, as an average, 5000 pounds of nitrogen and 1200 pounds of phosphorus, or nearly four times as much of each of those elements as this Virginia soil which you say is too poor to cultivate. "I wrote to the Illinois Experiment Station before I left Washington to see if I could get the average composition of the heavier prairie soil, which occupies the very flat areas that were originally swampy, and one of the letters you had received for me gives 8000 pounds of nitrogen and 2000 pounds of phosphorus as the general average for that soil. That is our most productive land, and it contains about five times as much of these two very important elements as your poorest land. "Our more common Illinois prairie contains about 35,000 pounds of potassium, 9,000 pounds of magnesium, and I 1,000 pounds of calcium. This is more than twice as much potassium and nearly three times as much magnesium as in your poorest land, but the calcium content is about the same in your soil as in ours. However, as you will remember, your soil is distinctly acid and consequently markedly in need of lime, the magnesium and calcium evidently being contained in part in the form of acid silicates with no carbonates; whereas, our brown silt loam is a neutral soil and our black clay loam contains much calcium carbonate, the same compound as pure limestone." "I am anxious to know about our best land," said Mr. West. "What did the chemist find in the soil from the slope where we get the best corn after breaking up the old pastures?" "He found the following amounts in the surface soil," said Percy. 800 pounds of nitrogen 1,660 pounds of phosphorus 34, 100 pounds of potassium 8,500 pounds of magnesium 13,100 pounds of calcium "Rich in everything but nitrogen," Percy continued, "richer than our common prairies in phosphorus and calcium, and nearly as rich in potassium and magnesium; but very, very poor in nitrogen. Legume plants ought to grow well on that land, because the minerals are present in abundance, and, while lack of nitrogen in the soil will limit the yield of all grains and grasses, there is no nitrogen limit for the legume plants if infected with the proper nitrogen-fixing bacteria, provided, of course, that the soil is not acid. You will remember, however, that even this sloping land is more or less acid, although here and there we found pieces of undecomposed limestone. With a liberal use of ground limestone, any legumes suited to this soil and climate ought to grow luxuriantly on those slopes."