The Story of the Soil Part 15

"Sixty"

"Corn?"

"Fifty-six pounds of sh.e.l.led 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 pota.s.sium, 117 pounds of calcium.

"It is just as easy to think in these terms as in per cent. or pounds of b.u.t.ter 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 a.n.a.lysis."

"Neither do I see how any one but a chemist could make much use of the reports which the a.n.a.lyst 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 const.i.tuents 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, pota.s.sium, 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 pota.s.sium 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 pota.s.sium 8,600 pounds of magnesium 5,400 pounds of calcium.

"From these figures you will see that the a.n.a.lysis 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 a.n.a.lysis 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 a.n.a.lysis 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 a.n.a.lysis with reference to the adoption of methods of soil improvement."

"Is the report of the a.n.a.lysis as confusing with respect to other elements as with pota.s.sium 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 a.n.a.lysis 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 a.n.a.lytical statement, a.s.suming apparently that the farmer would understand that the a.n.a.lytical statement did not mean what it said."

"But some soils do contain lime, do they not?"

"Some soils contain limestone," replied Percy, "and the a.n.a.lysis 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 sc.r.a.ping 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 quant.i.ty of soil was bagged from each stratum; and twenty such borings taken with an auger about one inch in diameter make a sufficient quant.i.ty 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 cla.s.sic 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?"