The Story of the Soil; from the Basis of Absolute Science and Real Life

by Cyril G. Hopkins

CHAPTER XXII

THE CHEMIST'S LABORATORY

THE Chief showed Percy into the laboratories of the Bureau and introduced him to the soil physicist and the soil chemist. Percy was greatly interested in the various lines of work in progress and gladly accepted an invitation to return after lunch and become better acquainted with the methods of investigation used.

In the afternoon the physicist showed him how the soil water could be removed from an ordinary moist soil by centrifugal force, and the chemist was growing wheat seedlings in small quantities of this water and in water extracts contained in bottles. The seedlings were allowed to grow for twenty days and then other seedlings were started in the same solution and also in fresh solution, and it was very apparent that in some cases the wheat grew better in the fresh solutions.

The chemist explained that he also analyzed the soil solutions and water extracts from different soils and that there was no relation between the crop yields and the chemical composition of the soils.

"But it seems to me," said Percy, "that your analysis refers to the plant food dissolved in the soil water only at the time when you extract it. How long a time does it require to make the extraction?"

"As a rule we shake the soil with water for three minutes and then it takes twenty minutes to separate the water from the soil. This gives us the plant food in solution and with the addition of more water the nitrates, phosphoric acid, and potash in the soil immediately dissolve sufficiently give us a nutrient solution of the same concentration as we had before. Thus there is always sufficient plant food in the soil so long as there is any of the original stock."

"That is surely quick work," said Percy, "but I wonder if the corn plant might not get somewhat different results from the soil analysis which it makes."

"How do you mean?"

"Did you ever plant a field of corn and then cultivate it and watch it grow with increasing rapidity, until along about the Fourth of July every leaf seemed to nod its appreciation and thanks as you stirred the soil; and to show its gratitude, too, by growing about five inches every twenty-four hours when the nights were warm?"

"No," replied the Chemist, "I have never had any experience of that sort. I am devoting my life to the more scientific investigations relating to the fundamental laws which underlie these soil fertility problems."

"Well, I was only thinking," Percy continued, "that you analyze a fraction of a pound of soil in a few minutes, while the corn plant analyzes about a ton of soil by a sort of continuous process, which covers twenty-four hours every day for about one hundred and twenty days, and it takes into account every change in temperature and moisture, the aeration with any variation produced by cultivation, and also the changes brought about by the nitrifying bacteria and all other agencies that promote the decomposition of the soil and the liberation of plant food, including the action upon the insoluble phosphates and other minerals of the carbonic acid exhaled by the roots of the corn plants, the nitric acid produced by the process of nitrification, and the various acids resulting from the decay of organic matter contained in the soil."

"I am very familiar with the literature of the whole subject of soil fertility," replied the Chemist, "and our theories are being accepted everywhere. I have just returned from a lecture tour extending from Florida to Michigan, and our ideas and methods are being very generally adopted, not only in this country but also in Europe."

"The Chief of the Bureau very kindly permitted me to look over the maps and reports relating to the soils of Maryland and Virginia," said Percy, "but in this literature I found no data as to the amount of plant food contained in the various soil types that have been found in the surveys. May I ask if the Bureau has made any analyses to ascertain the total amounts of the different essential plant food elements contained in these different soils?"

"No," the Chemist replied, "a chemical analysis gives practically no information concerning the fertility of the soil. We have made no ultimate analyses of soils, although we have used the same methods of analysis in a study of the partial composition of the soil separates, or particles of different grades, such as the sand, the silt, and the clay."

"And have you also determined the percentages of sand, silt, and clay in the soils themselves?"

"Oh, yes, the physical composition of the soil is a matter of very great importance, and this is always determined and reported for every soil. Did you not see that in the Reports you examined this morning?"

"I think I did notice it," Percy replied, "but it is so easy for the farmer himself to tell a sandy soil from a clay soil that I did not appreciate the value of those physical analyses.

"In any case, I shall be very glad to know what results were obtained from the chemical analysis of the soil separates to which you referred."

"Those results are all reported in Bulletin No. 54 of the Bureau of Soils," said the Chemist, "and I have extra copies right here and will be glad to present you with one. And let me give you our Bulletin 22 also. This will enable you to get a clear idea of the principles we are developing which are solving the soil fertility problems that have completely baffled the scientists heretofore."