The Story of the Soil Part 25

Adelaide colored and Percy now understood what had been a puzzle to him.

"The same bacteria," he went on quickly, "live upon both the sweet clover and the alfalfa, or at least they are interchangeable. These bacteria are not a fertilizer in any ordinary sense, but they are more in the nature of a disease, a kind of tuberculosis, as it were; except that they do much more good than harm. They attack the very tender young roots of the alfalfa and feed upon the nutritious sap, taking from it the phosphorus and other minerals and also the sugar or other carbohydrates needed for their own nourishment, since they have no power to secure carbon and oxygen from the air, as is done by all plants with green leaves. On the other hand, these bacteria have power to take the free nitrogen of the air, which enters the pores of the soil to some extent, and cause it to combine with food materials which are secured from the alfalfa sap, and thus the bacteria secure for themselves both nitrogen and the other essential plant foods. The alfalfa root or rootlet becomes enlarged at the point attacked by the bacteria, and a sort of wart or tubercle is formed which resembles a tiny potato, as large as clover seed on clover or alfalfa, and, singularly, about as large as peas on cowpeas or soy beans. On plants that are spa.r.s.ely infected, these tubercles develop to a large size and often in cl.u.s.ters. While the bacteria themselves are extremely small and can be seen only by the aid of a powerful microscope, the tubercles in which they live are easily seen, and they are sufficient to enable us to know whether the plants are infected."

"I wish you would tell me the difference between the words inoculated and infected," said Adelaide.

"Inoculated is used in the active sense and infected in the pa.s.sive," said Percy. "Thus the red clover growing in the field is infected if there are tubercles on its roots, although it may never have been inoculated; and we inoculate alfalfa because it would not be likely to become infected without direct inoculation."

"Under favorable conditions," continued Percy, "these bacteria multiply with tremendous rapidity, somewhat as the germs of small pox or yellow fever multiply if allowed to do so. A single tubercle may contain a million germs which if distributed uniformly over an acre would furnish more than twenty bacteria for every square foot."

"There, Charles," said the grandmother, "wouldn't a vest pocketful of those bugs or germs be a big enough dose for one acre?"

"Well, but they're not a fertilizer, Mother," said Mr. West, "and besides Mr. Johnston says it is better to use the infected sweet clover soil and there is no need of paying $2 an acre for something we knew nothing about, and especially on land that is not worth more than $2 an acre."

"I don't care what it's worth," she replied, "some of it cost your grandfather $68 an acre, and it will never be sold for any $2, while I have any say so about it."

They waited for Percy to proceed.

"The individual bacteria are very short-lived," he continued, "and products of decay soon begin to acc.u.mulate in the tubercles. These products contain, in combined form, nitrogen which the bacteria have taken from the air, and in this form it is taken from the tubercles and absorbed through the roots into the host plant and thus serves as a source of nitrogen for all of the agricultural legumes.

"It should be kept in mind, of course, that the red clover has one kind of nitrogen-fixing bacteria, that the cowpea has a different kind, and that the soy bean bacteria are still different, while a fourth kind lives on the roots of alfalfa and sweet clover."

"How much infected sweet clover soil would I need to inoculate an acre of land for alfalfa?" asked Mr. West.

"If the soil is thoroughly infected, a hundred pounds to the acre will do very well if applied at the same time the alfalfa seed is sown and immediately harrowed in with the seed. If allowed to lie for several hours or days exposed to the sunshine after being spread over the land the bacteria will be destroyed, for like most bacteria, such as those which lurk in milk pails to sour the milk, they are killed by the sunshine."

" That's right," said the grandmother. "That's the way to sterilize milk pails and pans and crocks. I like crocks better than pans. They don't have any sort of joints to dig out."

"Of course," continued Percy, "a wagon load of infected soil will make a more perfect inoculation than a hundred pounds, and where it costs nothing but the hauling it is well to use a liberal amount."

"How deep should it be taken?" asked Mr. West.

"About the same depth as you would plow. The tubercles are mostly within six or eight inches of the surface. The bacteria depend upon the nitrogen of the air and this must enter the surface soil.

Sometimes in wet weather the tubercles can be found almost at the surface of the ground, and when the ground cracks one can often find tubercles sticking out in the cracks an inch or two beneath the surface but protected from direct sunshine.

"These bacteria have power to furnish very large amounts of nitrogen to such a crop as alfalfa. The Illinois Station reports having grown eight and one-half tons of alfalfa per acre in one season. It was harvested in four cuttings. The hay itself was worth at least $6 a ton above all expenses, which would bring $51 an acre net profit for one year. Of course this was above the average, which is only about four and one-half tons over a series of several years. But suppose you can save only three tons and get $6 a ton net for it, as you could easily do by feeding it to your cattle and sheep. That would bring $18 an acre or six per cent. interest on $300 land. I am altogether confident that this could be done on your sloping hillsides, with their rich supplies of phosphorus and other mineral foods, provided, of course, that you use plenty of ground limestone and thoroughly inoculate the soil."

"Well, I shall certainly try alfalfa again," said Mr. West, "and if I can grow such crops of alfalfa as you think on the hillsides, I can have much more farm manure produced for the improvement of the rest of the land. By the way what did that chemist find in that sample you took of the other land where it does not wash so much as on the steeper slopes."

"He found the following:

1,030 pounds of nitrogen 1,270 pounds of phosphorus 16,500 pounds of pota.s.sium 7,460 pounds of magnesium 16,100 pounds of calcium

"Well, the phosphorus is not so low," said Mr. West.

"Fully equal to that in our $150 Illinois prairie," replied Percy, "and again the calcium is more than ours, with magnesium not far below, and pota.s.sium half our supply. Nitrogen is plainly the most serious problem on most of this farm, and limestone and legumes must solve that problem if properly used."

"Do you think this land could be made as valuable as the Illinois land just by a liberal use of limestone and legumes?" asked Adelaide.

"I should have some doubt about that," Percy replied. "Your very level uplands that neither lose nor receive material from surface washing are very deficient in phosphorus and much poorer than ours in pota.s.sium and magnesium; and your undulating and steeply sloping lands are more or less broken, with many rock outcrops on the points and some impa.s.sable gullies, which as a rule compel the cultivation of the land in small irregular fields. A three-cornered field of from two to fifteen acres can never have quite the same value per acre as the land where forty or eighty acres of corn can be grown in a body with no necessity of omitting a single hill. Then there is some unavoidable loss from surface washing, so that to maintain the supply of organic matter and nitrogen will require a larger use of legumes than on level land of equal richness. In addition to this is the initial difference in humus content. This is well measured by the nitrogen content. While your soil contains eight hundred pounds of nitrogen on the steeper slopes and one thousand pounds on the more gently undulating areas, ours contains five thousand pounds in the brown silt loam and eight thousand pounds in the heavier black clay loam. This means that our Illinois prairie soil contains from five to ten times as much humus, or organic matter, as your best upland soil. To supply this difference in humus would require the addition of from four hundred to eight hundred tons per acre of average farm manure, or the plowing under of one hundred to two hundred tons of air-dry clover. This represents the great reserve of the Illinois prairie soils above the total supplies remaining in your soils.

"Our farmers are still producing crops very largely by drawing on this reserve. Of course most of this great supply of humus is very old. It represents the organic residues most resistant to decomposition; and, where corn and oats are grown exclusively, the soil has reached a condition on many farms under which the decomposition of the reserve organic matter is so slow that the nitrogen liberated from its own decay and the minerals liberated from the soil by the action of the decomposition products are not sufficient to meet the requirements of large crops, and for this reason alone some of our lands that are still rich are said to be run down; but they only require a moderate use of clover or farm manure or other fresh and active organic matter to at once restore their productiveness to a point almost equal to the yields from the virgin soil. Some Illinois farmers who have discovered this apparent restoration have jumped to the conclusion that they have solved the problem of permanently maintaining the fertility of the soil; and I judge from a remark made by the Secretary of Agriculture that some Iowa farmers have the same mistaken notions.

"These fresh supplies of active organic matter serve primarily as soil stimulants, hastening the liberation of nitrogen from the organic reserve and of minerals from the inorganic soil materials.

"Where one of the Eastern farmers has managed a farm under the rotation system with the occasional use of clover or light applications of farm manure,--where this has been continued until the great reserve is largely gone, and the phosphorus supply greatly depleted, then the land is truly run down, but not until then.

"Finally, land-plaster and quick-lime, still more powerful soil stimulants, are often brought into the system to bring about a more complete exhaustion of the soil reserves, and lastly the use of small amounts of high-priced commercial fertilizers serves to put the land in suitable condition for ultimate abandonment."

"Do you mean that commercial fertilizers injure the soil?" asked Mr.

West.

"Well, to some extent they injure the soil because they tend to destroy the limestone and increase the acidity of the soil, and also because they contain more or less manufactured land-plaster and thus serve as soil stimulants; but the chief point to keep in mind concerning the use of the common so-called complete commercial fertilizer is that they are too expensive to permit their use in sufficient quant.i.ties to positively enrich the soil. Thus the farmer may apply two hundred pounds of such a fertilizer at a cost of $3.00 an acre, and then harvest a crop of wheat, two crops of hay, pasture for another year or two, plow up the grounds for corn, apply another two hundred pounds for the corn crop, follow with a crop of oats, and then repeat. He thus harvests five crops and pastures a year or two and applies perhaps four hundred pounds of fertilizer at a cost of $6.00.

"As an average of the most common commercial fertilizers sold to the farmers in the Eastern and Southern States, the four hundred pounds would add to the soil seven pounds of nitrogen, fourteen pounds of phosphorus and seven pounds of pota.s.sium, while a single fifty-bushel crop of corn will remove from the soil ten times as much nitrogen, five times as much pota.s.sium, and nearly as much phosphorus as the total amounts applied in this six-year or seven-year rotation.

"In this manner the farmer extends the time during which he can take from the soil crops whose value exceed their cost. He applies only one-fourth or possibly one-half as much of the most deficient element as the crops harvested require, and thus he continues for a longer time to 'work the land for all that's in it! '"

"Well, isn't that the limit?" said Adelaide, with emphasis on the "isn't," for which she received a disapproving look from her mother, so far as her almost angel-face could give such a look.

"So far as human ingenuity has yet devised," replied Percy, "this system appears to be the limit; but this limit has not yet been reached on any Westover soil. If anyone can devise a method for extending this limit he should apply it on a type of soil covering more than two-fifths of the total area of St. Mary County and more than 45,000 acres of Prince George County, Maryland, some of which almost adjoins the District of Columbia. This soil has been reduced in fertility until it contains only one-third as much phosphorus as your poorest land. I found a Western man who had come down to Maryland a few years ago. He saw that beautiful almost level upland soil, and it looked so good to him that he bought and kept buying until he had 'squared out' a tract of eleven hundred acres. He still had left money enough to fence the farm and to put the buildings in good repair. He was a live-stock farmer from the West who just knew from his own experience and from that of the Secretary of Agriculture, in the use of a little clover or farm manure in unlocking the great reserves of an almost virgin soil, that all his Maryland farm needed was clover seed and live stock. Sheep especially he knew to be great producers of fertility.

"He sowed the clover and gra.s.s seed and they germinated well. He even secured a fine catch, but it failed to hold, as we say out West. He tried again and again, and failed as often as he tried. He showed me his best clover on a field that had received some manure made from feed part of which was purchased, and that had also received five hundred pounds per acre of hydrated lime, which he was finally persuaded to use, after becoming convinced that clover-growing on old abandoned land was not exactly as easy as clover-growing on a 'run-down' farm of almost virgin soil in the West."

"And was the clover good after that treatment?" asked Mr. West.

"No, not good," said Percy, "but in some places where the manure had been applied to the high points, as is the custom of the Western farmer, the yield of clover, weeds, and foul gra.s.s together must have been nearly a half ton to the acre. Fortunately he waited to fully stock his farm with cattle and sheep until he should have some a.s.surance of producing sufficient feed to keep them for a time at least, instead of making the common mistake of the less experienced farmer who goes to the country from the city, and who imagines that, if he has plenty of stock on the farm, they must of necessity produce abundance of manure with which to enrich his land for the production of abundant crops."

"Well, now you'll have to show me," said the grandmother. "To my way of thinking that's a pretty good kind of a notion for a farmer to have, and I'd like to know what's wrong with it."

Again a shadow seemed to cross the sweet face as the mother's glance turned from grandma to Adelaide.

"The system has some merit," replied Percy, "but it starts at the wrong point in the circle. Cattle and sheep must first have feed before they can produce the fertilizer with which to enrich the soil; and people who would raise stock on poor land should always produce a good supply of food before they procure the stock requiring to be fed. There is probably no more direct route to financial disaster than for one to insist upon over-stocking a farm that is essentially worn out."

"But doesn't pasturing enrich the soil?" asked the grandmother.

"Pasturing may enrich the soil only in a single element of plant food," said Percy. "In all other elements simple pasturing must always contribute toward soil depletion. If the pasture herbage contains a sufficient proportion of legume plants so that the fixation of free nitrogen exceeds the utilization of nitrogen in animal growth, then the soil will be enriched in that element, although with the same growth of plants it would be enriched more rapidly without pasturing; for animals are not made out of nothing.

Meat, milk, and wool are all highly nitrogenous products.

"On the other hand no amount of pasturing can add to the soil a single pound of any one of the six mineral elements, and phosphorus, which is normally the most limited of all these elements, is abstracted from the soil and retained by the animals in very considerable amounts. As an average one-fourth of the phosphorus contained in the food consumed is retained in the animal products, especially in bone, flesh, and milk."

"Well, I didn't know that milk contained phosphorus," said Mr. West, "although I did know, of course, that phosphorus must be contained in bone."

"But, as you know," said Percy, "milk is the only food of young animals, and they must secure their bone food from the milk.

Furthermore, the complete a.n.a.lysis of milk shows that it contains very considerable quant.i.ties. There are also records of digestion experiments in which less than one-half of the phosphorus in the food consumed was recovered in the total manural excrements. As a matter of fact there is a time in the life of the young mother, as with the two-year old cow, for example, when she must abstract from the food she consumes sufficient phosphorus for the nourishment of three growing animals,--her own immature body, a suckling calf, and another calf as yet unborn.

"Of course the organic matter of the soil should increase under pasturing, especially under conditions that make possible an acc.u.mulation of nitrogen; but here too the animals make no contribution toward any such acc.u.mulation. With the same growth of plants the acc.u.mulation of organic matter would be much more rapid without live stock."

"It is known absolutely but not generally that live stock destroy about two-thirds of the organic matter contained in the food they consume. With grains the proportion is higher, and with coa.r.s.e forage it is lower, but as an average about two-thirds of the dry matter in tender young gra.s.s or clover or in a mixed, well-balanced ration of grain and hay is digested and thus practically destroyed so far as the production of organic matter is concerned.