THE GREAT LABORATORY.* ROMANCE was found in the soil when
it ceased to be thought of as dead mass and was discovered to be a living, moving world. It is moving, as Mr. Fletcher shows in this remark- ably readable book, not only in the sense understood by the geologist when he explains that "within the lifetime of one man a hill may become appreciably lower" or that "the whole earth is being levelled." Nor is it moving only in the way in which ants have brought to the surface of a four-acre field yearly enough fine soil to cover the entire area a fifth of an inch deep, or in which the twenty-five to fifty thousand worms in an acre pass through their bodies each year ten tons of earth. The soil is heaving with microscopic life. And we are merely at the beginning of our knowledge of it, for bacteriology is still young, and the soil, the basis of agri- culture and the foundation of wealth, has until lately received little minute study.
It is difficult to realise into what fine particles soil may be divided. Grass is often growing in soil containing four hundred million particles to the ounce. These particles are not, of course, sucked up by the plant as was once supposed. What the rootlets feed on is the film-water which surrounds and slowly dissolves the soil-grains. If an acre of clay-loam three-quarters of a foot deep may be estimated to weigh three million pounds or more, and we assume that there is merely a
• Suits. By B. W. Fletcher. Illustrated. London: A. Constable and Co. [as. Ga. j tenth of one per cent. of nitrogen in it, it must contain upwards of three thousand pounds of that plant-food. Pro- portionately, the farmer's application of " artificials" to the soil is inconsiderable, for the distribution is only at the rate of from thirty to seventy-five pounds an acre. But immense
though the reserve of plant-food in the soil is, the great store- house of fertility is not the earth but the air. More than ninety per cent. of the crops taken from the field comes from the atmosphere. From the air there are taken oxygen, hydrogen, and carbon, and, as the New England farmer said, it is "mighty lucky" that the supply of these plant-foods is, as far as we know, inexhaustible. The water in the soil of most importance is not the bottom, or standing, water, or the small amount absorbed from the air—there is air in the soil, just as there is air at the bottom of a corn-bin—but the film-water, the direct supply of the plants. The driest soil when squeezed gives evidence of the presence of this film-
water. A good farm soil may hold more than half its weight of film-water. The part which drainage plays in warming a soil may be imagined from the fact that there may be a
difference of from seven to ten degrees in the temperature of well-drained and badly-drained ground. The coarser a soil is the more it holds the beat. Have not gardeners put loose gravel round vines to keep them warm during the night ? The colour of a soil is of importance as well as its texture. A dark-coloured soil is usually warmer than a light- coloured—horticulturists in Saxony ripen melons with the aid of a layer of coal-dust—and one of the benefits the soil gets from the addition of humus is that it is darkened. When corn is "drowned out" it dies chiefly because, owing to the spaces between the particles of soil being overcharged with water, the rootlets cannot breathe. Air is also needed in the soil to make more plant-food. A well-drained, open soil has in it most life, fermentation, and fertility.
Tillage helps the aeration of the soil. So does drainage. As the water is drawn out, the air rushes in. The soil is not the same this year as it was last. There have been physical, chemical, and bacterial changes. As there are said to be
fifty thousand germs in 0.032 of a troy ounce of fertile soil, the bacterial changes alone must be remarkable. The
germs to which most attention has been given are the
nitrogen-fixers. In the matter of nitrogen it is a case, with other than leguminous plants, of nitrogen, nitrogen every-
where and not a drop to drink. The air contains vast quantities of nitrogen, but the plants cannot get hold of it. They have to be content with the nitrogen which is in the soil in an available form. It might be thought that they are well off, for lying near them is the nitrogen from the bodies of dead plants. But this nitrogen has been returned to the soil as organic nitrogen, a compound which will not dissolve in water; and plants can take food from the soil through the medium of water only. The work of converting the useless organic nitrogen into usable nitrate is done by the nitrogen- fixing germs, found in all fertile soils. Provided that they have plenty of phosphoric acid and rotted vegetation, that there is moisture, ventilation, and a medium temperature, and that the soil does not lack lime, they will do their work like yeast in the housewife's dough.
There are nitrogen-fixing germs, however, which take nitrogen, not from humus, but from the air itself. They are so small that ten thousand of them placed side by side would be needed to measure an inch. They live in the curious nodules or tubercles which may be seen on the roots of beaus, clover, lucerne, or any leguminous plant. They take the nitrogen from the soil-air and turn it over to the plant which is their host. There are two ways in which leguminous plants can be supplied with bacteria. The soil in a field in which legumes have been grown successfully contains millions of the desired organisms. All that is necessary, then, is to sow soil from this field at the rate of from four hundred to eight hundred pounds an acre in the ground which lacks bacteria. The second way in which to impart bacteria is to buy one of the artificial cultures. If the culture has been properly made—there is virtue in an " if "—and it is dissolved in warm water, and sprinkled on a quantity of soil, which is then scattered over the field in which legumes are to be planted, success is as likely as with a distribution of bacteria- impregnated soil from an old beanfield. It is remarkable that if leguminous plants are growing in soil which is well supplied with available nitrogen, they obtain little nitrogen from the air. Plants on a poor soil always have more nodules on their roots than plants on a rich one. But even on a soil rich in nitrogen, leguminous crops—as the farmer knows from experi- ence when he arranges to sow wheat after beans—return more nitrogen to the soil than they take from it. Thorough tillage and good drainage not only help the nitrogen-fixers in their work ; they discourage the nitrogen-wasting bacteria which are pitted against them. These are, however, only one variety of the myriad soil-bacteria—" many beneficial, most of them harmless, some injurious "—which, as in the case of "clover-sickness," give to the studious farmer only too plain an indication of their existence. "It seems not improbable," says Mr. Fletcher, "that the agriculturists of some future generation may be able to inoculate their soils with different beneficial bacteria and secure specific and valuable results, much as the butter-maker secures certain flavours with certain cultures."
But there are other agencies at work in the soil than bacteria. The plant-food in most of the fertilisers applied to the soil would be quickly wasted if chemical changes did not hold it until the rootlets of plants could use it. "Plants feed," as the author writes, "not upon the materials we apply to the soil, but upon the chemical compounds formed in the soil by them. The soil is a great chemical laboratory. Numberless new adjustments of the partnerships between the elements occur every hour. No chemist holds the beaker or fires the great retort; the changes take place in obedience to natural laws, quietly and methodically, yet with results so far-reaching that we can hardly grasp their significance." As the fertiliser solution on which the plants feed is so weak that man drinks it as pure water—almost any kind of farm plant will grow very well in the water caught from a drain-tile—it follows that they have to consume a great deal of it. The water needed to grow a ton of hay—account is taken of what is used by the plant and evaporated from the soil—would cover an acre more than a foot deep. There is always a steady current of film-water creeping from soil-particle to soil- particle, and from space to space between them, to the root- hairs of every thirsty plant. The film of water adheres to the particles as water adheres to a pebble taken from a pond. There is also a current of film-water passing upwards every summer day to replace the water that the uppermost soil has lost by evaporation. The great volume of film-water moving in these two currents "we may think of," says Mr. Fletcher, "as equal to a layer of water over fifteen inches deep in the first five feet of some soils." What may be done to atop the evaporation of water from the surface—more than a pound a day per square foot of farm soil, it has been estimated— the conservation of which is one of the most important problems in husbandry ? Obviously, we may block up by mulching with loose dry soil the tops of the tubes by which the water may be imagined to be drawn up as oil is drawn up through a lamp-wick. Unfortunately, until weeds have sprung up, too many occupiers of land do not give the soil the tillage which would save moisture and set free plant-food as well. From this point of view, weeds may be regarded as a blessing. As to keeping up the fertility of the soil, Mr. Fletcher might have used the old argument that the original meaning of manuring was not to add a fertiliser, but to "work by the hand." The soil contains incredible quantities of soil-food. So-called worn- out soils, which hardly yield enough to pay for cropping them, have been proved to hold per acre, in the top eight inches alone, not far short of four thousand pounds of nitrogen, six thousand pounds of phosphoric acid, and ;twenty thousand pounds of potash. The modern soil-doctor prescribes for the land less medicine and more attention to exercise and general condition. It is, he contends, not fertilisers, but tillage, rotation of crops, and the addition of humus in the form of farmyard manure and ploughed-in green-crops which unhealthy soil needs in order to regain its vigour. "The key to maintaining the fertility of the soil," an old farmer reasoned, "is to have plants decaying in it all the time, as in uncleared land." This theory, as Mr. Fletcher urges in a book which, by reason of its excellent illustrations as well as its facts, is a useful addition to current agricultural literature, means curtailing the often extravagant use of " artificials," and relying more on Nature's methods. In the United States alone there have been spent on fertilisers during the last five years not far short of a billion dollars i
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