to such an extent that the people required all their energies to
secure a living."






CHAPTER XVII

MORE PROBLEMS





"NOW let us give Mr. Johnston a chance to tell us about the nitrogen
problem," said Mr. Thornton. "I'm pretty well satisfied with the
natural circulation of carbon, oxygen, and hydrogen; but I want to
understand all I can of the practical methods of securing and
utilizing nitrogen; and we have heard almost nothing about the other
six essential elements which the soil must furnish. Let me see.--I
think you said that iron, calcium, magnesium and potassium are
usually abundant in the soil, while phosphorus and sulfur are very
limited."

"Yes, that is the rule under general or average conditions, but it
should be stated that the amount of sulfur required by plants is
very small as compared with phosphorus, a difference which places a
great distinction between them. Besides considerable quantities of