Lessons on Soil

Fig. 33 shows two pots of wheat, one kept only just sufficiently moist for growth, the other kept very moist but not too wet. You can see what a difference there is; in the drier pot the leaves are rather narrow and the plants are small, in the moister pot the leaves are wide and the plants big. But there was also another difference that the photograph does not bring out very well—the plants in the rather dry soil were, as you can see, in full ear, ripe and yellow, while those in the very moist soil were still green and growing. We see then

(1) that on moist soils there is greater growth than on dry soils, but the plants do not ripen so quickly;

(2) in very wet soils mustard—and many other plants also—will not grow.

Water is not itself harmful. It is easy to grow many plants in water containing the proper food, but air must be blown through the water at frequent intervals. In the water-logged soil of Pot 15 the trouble arose not from too much water but from too little air. Air is wanted because plants are living and breathing in every part, in the roots as well as in the leaves.

Now turn to what you have seen in your walks. You would probably notice that on the drier, sandy or gravel ground there was nothing like as great a growth of grass or of other plants as on the moister soil. This is so much like what we found in the pot experiments that we shall not be wrong in supposing that the difference in water supply largely accounted for the difference in growth. But you may also have noticed something else. Plants in the drier soil have generally narrow leaves and the grasses are rolled up and fine, whilst those on the damp soil, including the grasses, have usually broad leaves. Thus in the dry sandy soil you may find broom, spurrey, sheep's fescue, pine trees, all with narrow leaves; whilst on the moister soil you may find burdock, primroses, cocksfoot and other broad-leaved plants. Figs. 34 a and b show some plants we found on a dry, gravelly patch on Harpenden common, and on a moist loam in the river valley below.

Before we can account for this observation, we must ascertain a little more closely what becomes of the water the plant takes up. It certainly does not all stay in the plant, and the only way out seems to be through the leaves. Put a test tube on the leaf of a growing plant and fix a split cork round the stem: leave in sunlight for a few hours and notice that water begins to collect in the test tube (Fig. 35). The experiment shows that water passes out of the plant through the leaves.

This experiment was first made by Stephen Hales, and described by him thus in 1727: "Having by many evident proofs in the foregoing experiments seen the great quantities of liquor that were imbibed and perspired by trees, I was desirous to try if I could get any of this perspiring matter; and in order to do it, I took several glass chymical retorts, b a p [Fig. 36] and put the boughs of several sorts of trees, as they were growing with their leaves on, into the retorts, stopping up the mouth p of the retorts with bladder. By this means I got several ounces of the perspiring matter of vines, figtrees"—and other trees, which "matter" Hales found to be almost pure water. The test tube experiment should now be made with a narrow-leaved grass like sheep's fescue and with a wide-leaved grass like cocksfoot. You will find that wide-leaved plants pass out more water than those with narrow leaves, and hence wide-leaved plants occur in damp situations or on damp soils like loams and clays, while narrow-leaved plants can grow on dry, sandy soils.

Another thing you will notice is that fields lying at the side of a river and liable to be flooded, and fields high up in wet hill districts, are covered with grass. In a clay country there is also a great deal of grass land and not much ploughed land; if you live where there is much clay you can easily discover the reason. Clay becomes very wet and sticky when rain falls, and very hard in dry weather: it is, therefore, difficult to cultivate. Farmers cannot afford to spend too much money on cultivation, and so they prefer grass, because once it is established it goes on indefinitely and does not want ploughing up and re-sowing. And besides, farmers have learned by experience that grass can tolerate more water and less warmth than most other English crops. There is much more grass land in those parts of England where the rainfall is high and the temperature rather low—e.g. the northern parts of England—than in the eastern counties where the rainfall is low.

Plants require to be sufficiently warm. Some like tropical heat and can only be grown in hot houses; others can withstand a certain amount of cold and will grow up on the mountains. Our common cultivated crops come in between and will not grow in too cold or exposed a situation; thus you find very little cultivated land 800 ft. above sea level, and not usually much above 500 ft. At this height it is left as grass land, and higher up as woodland, moor, or waste land. Grass requires less warmth and can therefore grow at greater heights than many other crops. If you start at the top of a hill in Derbyshire, and walk down, you will see that the top is moorland, lower down comes grass land, still lower you may find arable land, and if the valley is damp you will find more grass at the bottom. Figs. 37 and 38 show typical views of the hill slopes further south: they are taken near Harpenden. The top of the hill in each case is over 400 ft. above sea level, and has never been thought worth cultivating, but has always been left as wood because it is too exposed for farm crops. On the lower slopes the arable fields are seen, while at the bottom bordering the river is rough grass land, shown in Fig. 39. The top is too cold and windy, and the bottom too wet, to be worth cultivating.

Situations more than five or six hundred feet above sea level are, in England, as a rule, too bleak and exposed for the ordinary cultivated crops. Such land is, therefore, either grass land, moorland, downland or woodland.

The roots of plants are living and require air. The soil must not be trodden too hard round them or air cannot get in, nor can it if too much water is present.

Grass can put up with more water and less warmth than most cultivated crops.

CHAPTER IX

CULTIVATION AND TILLAGE

Apparatus required.

Plot experiments, hoeing and mulching. Thermometer. Soil sampler (Fig. 42, p. 88). This tool consists of a steel tube 2 in. in diameter and 9 in. long, with a slit cut along its length and all the edges sharpened. The tube is fixed on to a vertical steel rod, bent at the end to a ring 2 in. in diameter, through which a stout wooden handle passes. It is readily made by a blacksmith.

Farmers and gardeners throughout the spring, summer and autumn, are busy ploughing or digging, hoeing or in other ways cultivating the soil. Unless all this is well done the soil fails to produce much; the sluggard's garden has always been a by-word and a reproach. In trying to understand why they do it we must remember that plant roots need water, warmth and air; if the soil is too compact or if there is too much water the plant suffers, as we have seen.

One great object of cultivation is, therefore, to prevent the soil being too compact and too wet. After the harvest the farmer breaks up his ground with a plough and then leaves it alone till seed time (Fig. 40). A gardener does the same thing with a fork in his kitchen garden—he cannot very well elsewhere, or the plant roots might become too cold. If there is frost during the winter both farmer and gardener are pleased because they say the frost "mellows" the ground; you can see what they mean if you walk on a frosty morning over a ploughed field. The large clods of earth are no longer sticky, they already show signs of breaking up, and if they are not frozen too hard can easily be shattered by a kick. The change has been brought about in exactly the same way as the bursting of water-pipes by frost. When water freezes it expands with enormous force and bursts open anything that confines it; water freezing in the pores of the soil forces the little fragments apart. This action is so important that further illustrations should be looked for. A piece of wet chalk left out on a frosty night often crumbles to pieces. It is dangerous to climb cliffs in the early spring because pieces of rock that have been split off during the winter frosts by the expanding water may easily give way. Frost plays havoc with walls built of flints and with old bricks that are beginning to wear. If there are several frosts, with falls of rain or snow and thaws coining in between, the soil is moved about a good deal by the freezing and melting water. Bulbs and cuttings are sometimes forced out of the ground, whilst grass and young wheat may be so loosened that they have to be rolled in again as soon as the weather permits. When the ground has been dug in autumn and left in a very rough state all this loosening work of the frost is very much helped, because so much of the soil may become frozen. If in spring you dig a piece of land that has already been dug in autumn, and then try digging a piece that has not, you will find the first much easier work than the second in all but very sandy soils.

A little before the seeds are sown, the soil has to be dug or cultivated again so that it may become more level and broken into smaller pieces. The farmer then harrows and the gardener rakes it, and it becomes still finer. Very great care is bestowed on the preparation of the seed bed, and it will take you longer to learn this than any other part of outdoor gardening. The soil has to be made fine and dry, and no pains must be spared in getting it so.

When at last the soil is fine enough the seed is put in. But it is not enough simply to let the seed tumble into the ground. It has to be pressed in gently with a spade or a roller, not too hard or the soil becomes too sticky. Fig. 41 shows this operation being carried out on the farm. Then the soil should be left alone.

If you watch an allotment holder who grows onions really well working away at his seed-bed you will see what a beautifully fine tilth he gets. If you try to do the same you will probably fail; his seeds will be up before yours and will grow into healthier plants. Only after long practice will you succeed, and then you will have mastered one of the great mysteries of gardening.

As soon as the plants are up they have to be hoed, and the more often this is done the better. Hoeing has several useful effects on the soil; during summer time some experiments may be made to find out what these are. A piece of ground is wanted that has got no crop on it. Set out three strips each six feet wide and six feet long, leave one entirely alone, hoe the second once a week, and the third three times a week; put labels on so that no mistake can arise. The surface of the untouched plot becomes very compact and glazed in appearance; the other soils look nice and crumbly. Take the temperature of the soils by placing a thermometer into it at various depths—half inch, three inches, and six inches—also take the temperature of the air; enter up the results as in the table, which shows what happened at Harpenden.

The thermometer readings are in degrees centigrade.

Remarks. June 20th: Hot sunny day, there had been no rain since June 11th.

June 27th: Cold, cloudy day, several cold, wet days during the past week.

On the cold day there was very little difference between the plots, but on the hot day the hoed plots were cooler than the others. Now only the top inch is touched by the hoe, and so it appears that the layer thus loosened shields the rest of the soil from the sun's heat. If this is the case we ought to find that any other loose material would act in just the same way. We must, therefore, set out a fourth plot alongside the others, cover it with straw or cut grass (a cover like this is called a mulch), and take the temperature there. Some of the results were as follows:—

Remarks. Sept. 24th: Warm day after a rather cold spell. Oct. 5th: After a long spell of dry, warm weather.

The untouched plot had become smothered in weeds and could no longer be used for this experiment. The mulched soil is, however, cooler even than the hoed soil, and our expectation that mulching would keep the soil cool has turned out to be correct.

Remarks. June 4th; The weather is still cold and the summer has not yet begun.

June 20th: Hot day following on some hot, dry weather.

June 27th: Rain had recently fallen.

When hoeing is done in the early part of the summer it dries the soil, and the more frequent the hoeing the drier the soil (see June 4th results). But later on, when the hot weather begins, the hoed soil loses much less moisture than the untouched plot; the latter lost 6.4 per cent. in 16 days in the top six inches, whilst the soil hoed once weekly lost 3.1 per cent., and the one hoed three times weekly lost only 1.4; the two hoed soils are now equal, and are both moister than the untouched soil. When more rain comes they get just as wet as the others: hoeing does not prevent water from sinking in, but it does prevent water from getting lost.

Our experiment has, therefore, shown us that hoeing makes a loose layer of soil which shields the rest of the soil from the sun's heat, and prevents it getting too hot or too dry. A hoed soil is cooler and moister, and therefore better suited for the growth of plant roots than an unhoed soil.

The mulch of straw or dried grass was found to have the same effect in conserving the water as the loose layer of soil obtained by hoeing. Some results were:—

These results are so important that some indoor experiments should be made to furnish more proof. Fix up three inverted bell jars with corks and bent tubes as shown in Fig. 43, fill all with dry soil well pressed down, then add water carefully till it appears in the glass tubes. Next day mark with stamp paper the level of liquid in each tube and then leave one jar untouched, carefully cultivate with a penknife every two or three days the top quarter of an inch of the second, and cover the third with a layer of grass. After a week notice again the levels of the liquid and mark with paper; you find that the water has fallen most in the untouched jar, showing that more has been lost from this than from the jars covered with a mulch either of soil or of dry grass.

A slate or flat stone acts like a mulch; if you leave one on the soil for a few days in hot weather and then lift it up on a hot day you will see that the soil underneath is quite moist; you may also find several slugs or other animals that have gone there for the sake of the coolness and the moisture. Plants and trees also keep off the sun's heat and so make the soil cold and moist. Grass land is in summer and autumn, and even in early winter, cooler near the surface than bare land. At Harpenden we found:—

Even if the ground is not covered a certain amount of protection is still possible. Trees are often planted round ponds to prevent evaporation of the water. The wind helps to dry the soil very much, and a hedge that shields from the wind not only protects the crop but also keeps the soil moist: a road with high hedges at each side remains wet for a long time after more exposed parts have dried. The effect on the temperature can be well seen on a day when a N.E. wind is blowing. Fix up on a piece of the experimental ground a little hedge made of small pea-stakes or brushwood, and take the soil temperature at one inch depth, both on the windward and on the leeward side. Two results were:—

We have already seen that on the hot day, June 20th, the top half-inch of soil was hotter than the air: the mercury in the thermometer rose directly it was put into the soil. There is nothing very unusual about this; if you touch a piece of iron lying on the soil you find it hotter than the air. Lower down the soil had the same temperature as the air, and still lower it was cooler[1]. The sun's heat travels so slowly into the soil in summer that months pass before it gets far down, but then, as it takes so long to get in, it also takes a long time to get out, and it takes still longer to get either in or out if there is a mulch or if grass is growing.

During the early winter you may notice that the first fall of snow soon melts on the arable land but remains longer on the grass; towards the end of the winter, however, the reverse happens and the snow melts first on the grass. There is no difficulty in explaining this. The arable land is, as we have seen, warmer in autumn and early winter than grass land, and so it melts the snow more rapidly. But during winter the grass land loses its heat more slowly, and therefore it is warmer at the end of the winter than the arable land, hence the snow melts more quickly.

In Chap. V. it was pointed out that dark coloured soils rich in humus are greatly favoured by gardeners and farmers. The value of humus can easily be shown: take a sample of soil from a garden that has for a long time been well manured and another from a field close by—next to it if you can—and find the amounts of moisture present. Two soils at Rothamsted gave the following results:—

Humus, therefore, keeps the water in the soil and saves it from being lost.

Another beneficial effect of hoeing is to keep down weeds. Weeds overcrowd the plant, shut out light, take food and water, and occupy space. Few plants can compete against weeds, some fail very badly in the struggle. Sow two rows of maize two yards apart; keep one well hoed for a yard on each side and leave the other alone to struggle with the weeds that will grow. Fig. 44 shows the result of this experiment at St George's School. At Rothamsted a piece of wheat was left unharvested in 1882, and the plot has not been touched since; the wheat was allowed to shed its seed and to grow up without any attention. Weeds flourished, but the wheat did not; the next year there was but little wheat, and by 1886 only a few plants could be seen, so stunted that one would hardly recognise them. The ground still remains untouched, and is now the dense thicket seen in Fig. 45. Most of our land would become like this if it were neglected for a few years.

Farmers occasionally leave their ground without a crop for a whole year and cultivate it as often as they can to kill the weeds. This practice is called "fallowing," and is very ancient; it is much less common now that crops like mangolds and swedes are grown, which can, if necessary, be hoed all the summer.

We have already seen (p. 69) that ordinary cultivated plants will not live in a water-logged soil. Wherever there is an excess of water it must be removed before satisfactory results can be obtained. Fig. 46 shows a field of wheat in May where the crop is all but killed and only certain weeds survive on a patch of undrained land that lay wet all the winter. Draining land is difficult and somewhat expensive; trenches are first cut to a proper depth, and drain pipes are laid on the bottom, taking care that there is a gentle slope all the way to the ditch. The rain soaks into the soil and gets into the pipes, for they are not joined together like gas or water pipes, but left with little spaces in between; it then runs out into the ditch. Usually only clay soils need drainage, but occasionally sandy soils do also (see pp. 30, 106). A great deal of drainage was carried out in England between 1840 and 1860, and it led to a marked improvement in agriculture and in country life generally. There is, however, a great deal that wants doing now.

The addition of chalk or lime to soil was found in Chap. III. to improve it very much by making it less sticky and less impervious to air and water. Chalk or lime does more than this. It puts out of action certain injurious substances or acids that may be formed, and thus makes the conditions more favourable for plants and for the useful micro-organisms; farmers and gardeners express this by saying that it "sweetens the soil." A United States proverb runs: "A lime country is a rich country." Very many soils in England are improved by adding lime or chalk. There are considerable areas in the south-eastern and eastern counties where the soil is very chalky; here you find a wonderfully rich assortment of flowers and shrubs. Where there is too much chalk the soil is not fertile, because it lets water through too easily, as was shown on p. 26: but for this very reason it is admirable for residential purposes.

There are some exceptions to the rule that plants need lime. Some plants will not tolerate it at all; such are rhododendrons, azaleas, foxgloves, spurrey, and broom; wherever you see these growing you may be sure that lime is absent.

Lime really differs from chalk, but changes into it so quickly in the soil that the action of both is almost, though not quite, the same.

CHAPTER X

THE SOIL AND THE COUNTRYSIDE

In this chapter we want to put together much of what we have learned about the different kinds of soil, so that as we go about the country we may know what to look for on a clay soil, a sandy soil, and so on.

We have seen that clay holds water and is very wet and sticky in winter, while in summer it becomes hard and dry, and is liable to crack badly. "It greets a' winter and girns a' summer," as one of Dr John Brown's characters said of his soil. Clay soils are therefore hard to dig and expensive to cultivate: the farmer calls them heavy and usually prefers to put them into grass because once the grass is up it lasts as long as it is wanted and never needs to be resown. But in the days when we grew our own wheat, before we imported it from the United States and other countries, this clay land was widely cultivated for wheat and beans. So long as wheat was 60/- to 100/- a quarter it was a very profitable crop, but, when some forty years ago it fell to 40/- and then lower still, the land either went out of cultivation like the "derelict" farms of Essex, or it was changed to grass land and used for cattle grazing. Great was the distress that followed; some districts indeed were years in recovering. But new methods came in: the land near London was used for dairy farming, and elsewhere it was improved for grazing, and the clay districts, although completely changed, are now more prosperous again. Many of the fields still show the ridges or "lands" in which, when they grew wheat, they were laid up to let the water run away, and many of them keep their old names, but these are the only relics of the old days. The land is not, and never was, very valuable. The roads are wide, and on either side have wide waste strips cut up roughly by horse tracks, cart ruts and ant hills. Bracken, gorse, rushes, thistles and brambles grow there, and you may find many fine blackberries in September. The coarse Aira grass is found with its leaves as rough as files. The villages are often built round greens which serve as the village playground, where the boys and young men now play cricket and football, and their forefathers practised archery, played quoits and other games. On a few village greens the Maypole can still be seen, whilst the stocks in which offenders were placed are also left in some places.

The hedges are often high and straggling, and there are numerous woods and plantations containing much oak. Some of the woods are very ancient and probably form part of the primeval forests that once largely covered England. Epping Forest in Essex, the Forest of Blean and the King's Wood in Kent, have probably never been cultivated land. In the days when ships were made of oak these woods and hedges were very valuable, but now they are of little use as sources of timber. Instead they are valued for quite another reason: they afford shelter for foxes and for game birds. The clay districts are and always have been famous for fox hunting; the Pytchley, Quorn, Belvoir, and other celebrated packs have their homes in the broad, clay, grassy vales of the Midlands. The vale of Blackmoor and other clay regions are equally famous. The plantations and hedgerows are fine places for primroses and foxgloves, while in the pastures, and especially the poor pastures, are found the ox-eyed daisy and quaking grass, that make such fine nosegays, as well as that sure sign of poverty, the yellow rattle. But many of these poor pastures have been improved by draining, liming, and the use of suitable manures. Although the roads are better than they were (see p. 30) they are still often bad and lie wet for weeks together in winter, especially where the hedges are high. Numerous brick and tile yards may be found and iron ore is not uncommon; in some places it is worked now, in others it is no longer worked and nothing remains of the lost industry save only a few names of fields, of ponds, or of cottages.

We will study the cultivated sands first. As sand is not good plant food (p. 43) these soils want a lot of manure, and so are not good for ordinary farmers. But they are very easy to cultivate—for which reason they are called light soils—and can be dug at any time; seeds can be sown early, and early crops can be got. Consequently these soils are very useful for men doing special work like fattening winter and spring sheep, or producing special crops like fruit or potatoes, and for market gardeners who grow all sorts of vegetables, carrots, parsnips, potatoes, peas, and so on. Fig. 47 is a view of a highly cultivated sandy region in Kent showing gooseberries in the foreground, vegetables behind, and a hop garden behind that again.