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

by Cyril G. Hopkins

CHAPTER XVIII

CLOSER TO MOTHER EARTH

THE following day Percy collected soil samples to represent the common type of soil on the farm. In the main the land was nearly level and very uniform, although here and there were small areas which varied from the main type, and in places the variation was marked. Percy and his host devoted the entire day to an examination of the soils of the farm and the collection of the samples.

"The prevailing soil type is what would be called a loam," said Percy, "and a single set of composite samples will fairly represent at least three-fourths of the land on this farm.

"It seems to me that it is enough for the present to sample this prevailing type, and later, if you desire, you could collect samples of the minor types, of which there are at least three that are quite distinct."

"A loam soil is one that includes a fair proportion of the several groups of soil materials, including silt, clay, and sand."

"What is silt?" asked Mr. Thornton.

"Silt consists of the soil particles which are finer than sand,—too small in fact to be felt as soil grains by rubbing between the fingers, and yet it is distinctly granular, while clay is a mere plastic or sticky mass like dough. What are commonly called clay soils consist largely of silt, but contain enough true clay to bind the silt into a stiff mass. In the main such soils are silt loams, but when deficient in organic matter they are yellow in color as a rule, and all such material is usually called clay by the farmers."

"Well, I had no idea that it would take us a whole day to get enough dirt for an analysis," remarked Mr. Thornton, as they were collecting the samples late in the afternoon. "Five minutes would have been plenty of time for me, before I saw the holes you've bored to-day."

"The fact is," replied Percy, "that the most difficult work of the soil investigator is to collect the samples. Of course any one could fill these little bags with soil in five minutes, but the question is, what would the soil represent? It may represent little more than the hole it came out of, as would be the case where the soil had been disturbed by burrowing animals, or modified by surface accumulations, as where a stack may sometime have been burned. In the one case the subsoil may have been brought up and mixed with the surface, and in the other the mineral constituents taken from forty acres in a crop of clover may have been returned to one-tenth of an acre."

"Certainly such things have occurred on many farms," agreed Mr. Thornton, "and they may have occurred on this farm for all any one knows."

"Fifty tons of clover hay," continued Percy, after making a few computations, "would contain 400 pounds of phosphorus, 2400 pounds of potassium, 620 pounds of magnesium, and 2340 pounds of calcium."

"I don't see how you keep all those figures in your head," said Mr.
Johnston.

"How many pounds are there in a ton of hay?" asked Percy.

"Two thousand."

"How many pounds in a bushel of oats?"

"Thirty in Virginia, but thirty-two in Carolina."

"How many in a bushel of wheat?"

"Sixty"

"Corn?"

"Fifty-six pounds of shelled corn, or seventy pounds of ears."

"Potatoes?"

"Eighty-six pounds,—both kinds the same, but most States require sixty pounds for the Irish potatoes."

Percy laughed. "You see," he said, "you have more figures in your head than I have in mine. You have mentioned twice as many right here, without a moment's hesitation, as I try to remember for the plant food contained in clover. I like to keep in mind the requirements of large crops, such as it is possible to raise under our climatic conditions if we will provide the stuff the crops are made of, so far as we need to, and do the farm work as it should be done. I never try to remember how much plant food is required for twenty-two bushels of corn per acre, which is the average yield of Virginia for the last ten years, while an authentic record reports a yield of 239 bushels from an acre of land in South Carolina. On our little farm in Illinois we have one field of sixteen acres, which was used for a pasture and feed lot for many years by my grandfather and has been thoroughly tile-drained since I was born, that has produced as high as 2,015 bushels of corn in one season, thus making an average of 126 bushels per acre.

"What I try to remember is the plant food requirements for such crops as we ought to try to raise, if we do what ought to be done. I try to remember the plant food required for a hundred-bushel crop of corn, a hundred-bushel crop of oats, a fifty-bushel crop of wheat, and four tons of clover hay. It is an easy matter to divide these amounts by two, as I have really been doing here in the East where it is hard for people to think in terms of such crops as these lands ought to be made to produce.

"The requirements of the clover crop I certainly want to have in mind as a part of my little stock of ever-ready knowledge. It is not very hard to remember that a four-ton crop of clover hay, which we ought to harvest from one acre in two cuttings, contains:

160 pounds of nitrogen, 31 pounds of magnesium, 20 pounds of phosphorus, 120 pounds of potassium, 117 pounds of calcium.

"It is just as easy to think in these terms as in per cent. or pounds of butter fat, which I understand is the basis on which you sell your cream."

"Yes, I believe you are right in this matter, Mr. Johnston, but I have never been able to see how we could apply the figures reported from chemical analysis."

"Neither do I see how any one but a chemist could make much use of the reports which the analyst usually publishes. Such reports will usually show the percentages of moisture and so-called 'phosphoric acid,' for example, in a sample of clover hay, and perhaps the percentages of these constituents in a sample of soil; but to connect the requirements of the clover crop with the invoice of the soil demand more of a mental effort than I was prepared for before I went to the agricultural college.

"On the other hand we were taught in college that the plowed soil of an acre of our most common Illinois corn belt land contains only 1200 pounds of phosphorus, and that a hundred-bushel crop of corn takes twenty-three pounds of phosphorus out of the soil. Furthermore that about one pound of phosphorus per acre is lost annually in drainage water in humid regions. By dividing 1200 by 24 it is easy to see that fifty corn crops such as we ought to try to raise would require as much phosphorus as the present supply in our soil to a depth of about seven inches. Of course there is some phosphorus below seven inches, but it is the plowed soil we must depend upon to a very large extent. The oldest agricultural experiment station in the world is at Rothamsted, England. On two plots of ground in the same field where wheat has been grown every year for sixty years, the soil below the plow line has practically the same composition, but on one plot the average yield for the last fifty years has been thirteen bushels per acre, while on the other the yield of wheat has averaged thirty-seven bushels for the same fifty years."

"The same kind of wheat?" inquired Mr. Thornton.

"Yes, and great care has always been taken to have these two plots treated alike in all respects, save one."

"And what was that?"

"Plant food was regularly incorporated with the plowed soil of the high-yielding plot."

"You mean that farm manure was used?"

"No, not a pound of farm manure has been used on that plot for more than sixty years; and, furthermore, the two plots were very much alike at the beginning; but, to the high-yielding plot, nitrogen, phosphorus, potassium, magnesium, calcium, and sulfur have all been applied in suitable compounds every year."

"That is to say," observed Mr. Thornton, "that the land itself has produced thirteen bushels of wheat per acre and the plant food applied has produced twenty four bushels, making the total yield thirty-seven bushels on the fertilized land."

"That is certainly a fair way to state it," replied Percy.

" Well, that sounds as though something might be done with run-down lands. About what part of the twenty-four bushels increase would it take to pay for the fertilizers?"

"About 150 per cent. of it," Percy replied.

"One hundred and fifty per cent! Why, you can't have more than a hundred per cent. of anything."

"Oh, yes, you can. The twenty-four bushels are one hundred per cent. of what the fertilizers produced, and the land itself increased this by fifty per cent., so that the fertilized land produced one hundred and fifty per cent. of the increase from the plant food applied.

"Well, that's too much college mathematics for me; but do you mean to say that it would take the whole thirty-seven bushels to pay for the plant food that produced the increase of twenty-four bushels?"

"That is exactly what I mean. I see that you do not like percentage any better than I do. Really the acre is the best agricultural unit. We buy and sell the land itself by the acre; we report crop yields at so many bushels or tons per acre; we apply manure at so many loads or tons per acre; we apply so many hundred pounds of fertilizer per acre; sow our wheat and oats at so many pecks or bushels per acre; and we ought to know the invoice of plant food in the plowed soil of an acre and the amounts carried off in the crops removed from an acre.

"Now, referring again to these figures from the forty acres of clover at two tons per acre. If the eighty tons were burned and the ashes mixed with the surface soil on a tenth of an acre the increase per acre would be as follows:

4,000 pounds of phosphorus 24,000 pounds of potassium 6,200 pounds of magnesium 23,400 pounds of calcium.

"These, remember, are the amounts per acre that would be added to the soil by burning the eighty tons of clover on one-tenth of an acre.

"Now compare these figures with the total amounts of the same elements contained in the common corn belt prairie soil of Illinois, which are as follows:

1,200 pounds of phosphorus 35,000 pounds of potassium 8,600 pounds of magnesium 5,400 pounds of calcium.

"From these figures you will see that the analysis of a single sample of soil collected from a spot of ground that had sometimes received such an addition as this would be positively worse than worthless, because it would give false information, and that is much worse than no information.

"The methods of chemical analysis have been developed to a high degree of accuracy, and it is not a difficult matter to find a chemist who can make a correct analysis of the sample placed in his hands; but the chief difficulties lie, first, in securing samples of soil that will truly represent the type or types of soil on the farm; and, second, in the interpretation of the results of analysis with reference to the adoption of methods of soil improvement."

"Is the report of the analysis as confusing with respect to other elements as with potassium and phosphorus, which, I understand, are likely to be reported in terms of potash and a 'phosphoric acid' that is not true phosphoric acid?"

"Still worse," Percy replied. "The calcium is commonly reported in terms of lime, or, as you would say, quick lime; and vet the soil may be an acid soil, like yours, and contain no lime whatever, neither as quick lime nor limestone. I have seen an analysis reporting half a per cent. of calcium oxid, which would make five tons of quick lime in the plowed soil of an acre; whereas the soil not only contained no lime whatever, but was so acid that it needed five tons of ground limestone per acre to correct the acidity.

"The trouble is that when the chemist found calcium in the soil existing in the form of acid silicate, or calcium hydrogen silicate, he reported calcium oxid, or lime, in his analytical statement, assuming apparently that the farmer would understand that the analytical statement did not mean what it said."

"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."

"And what was the actual effect of the nitrogen?" questioned Mr. Thornton. "How much did the wheat yield when they left out the nitrogen and applied all the other elements?"

"Only fifteen bushels," was the reply.

"Only fifteen bushels! Only two bushels increase for all the other elements, phosphorus, potassium, magnesium, and calcium,—and I remember you said that sulfur also was applied. Why didn't they leave off all these other elements, and just use the nitrogen alone?"

"They did on another plot in the same field."

"Oh, they did do that? What was the yield on that plot?"

"Only twenty bushels."

"Only twenty bushels! Well, that s mighty queer. How do you account for that?"

"Does Mrs. Thornton sometimes make dough out of flour and milk?" asked Percy.

"Another Yankee question, eh?" said Mr. Thornton. "I told my wife once that I wished she could make the bread my mother used to make, and she said she wished I could make the dough her father used to make. Yes, my wife makes dough, a good deal more than I do, and she makes it of flour and milk, when we aren't reduced to corn meal and water."

"Can she make dough of flour alone?" continued Percy.

"No," replied Mr. Thornton.

"Nor of milk alone?"

"No."

"Well, wheat cannot be made of nitrogen alone, nor can it be made without nitrogen. On Broadbalk field at Rothamsted, where the wheat is grown, the soil is most deficient in the element nitrogen. In other words, nitrogen is the limiting element for wheat on that soil; and practically no increase can be made in the yield of wheat unless nitrogen is added. However, some other elements are not furnished by this soil in sufficient amount for the largest yield of wheat, and these place their limitation upon the crop at twenty bushels. To remove this second limitation requires that another element, such as phosphorus, shall be supplied in larger amount than is anually liberated in the soil under the system of farming practiced."

"Yes, I see that," said Mr. Thornton, "it's like eating pancakes and honey; the more cakes you have the more honey you want. I think I can almost see my way through in this matter; we are to correct the acid with limestone, to work the legumes for nitrogen, and turn under everything we can to increase the organic matter, and if we find that the soil won't furnish enough phosphorus, potassium, magnesium, or calcium, even with the help of the decaying organic matter to liberate them, why then it is up to us to increase the supply of those elements."

"You must remember that the calcium will be supplied in the limestone;" cautioned Percy. "And, if you use magnesian limestone, you will thus supply both calcium and magnesium. Keep in mind that _magnesian _only means that the limestone contains some magnesium. and that it is not a pure calcium carbonate. The purest magnesian limestone consists of a double carbonate of calcium and magnesium, called dolomite."

"But I have heard that magnesian lime is bad for soils," said Mr.
Thornton.

"That is true," Percy replied, "and so is ordinary lime bad for soils. The Germans say: 'Lime makes the fathers rich but the children poor.' The English saying is:

'Lime and lime without manure
Will make both farm and farmer poor.'

"Both of these national proverbs are correct for common, every-day lime; but you know, do you not, that limestone soils are usually very good and very durable soils?"

"That's what I've always heard," replied Mr. Thornton.

"Well, there is no danger whatever from using too much limestone; and all the information thus far secured shows that magnesian limestone is even better than the pure calcium limestone. I know two Illinois farmers who are using large quantities of ground magnesian limestone, and one of them has applied as much as twenty tons per acre. On that land his corn crop was good for eighty bushels per acre this year. Of course that heavy application was more than was needed, but initial applications of four or five tons are very satisfactory, and these should be followed by about two tons per acre every four to six years."

Mr. Thornton took his guest to Blairville that evening as they had planned and he assured Percy that should he decide to purchase land in that section they would let him have three hundred acres of their land at ten dollars an acre.

"I will let you know after I get the samples analyzed for you," said Percy. "The price is low enough and the location ideal, but still I want to have the invoice before I buy the goods. I will write you about sending the samples to the chemist after I hear from some I sent him from Montplain."