Produced by Al Haines
LESSONS ON SOIL
BY
E. J. RUSSELL, D.Sc. (Lond.)
GOLDSMITH COMPANY'S SOIL CHEMIST,
ROTHAMSTED EXPERIMENTAL STATION
Cambridge:
at the University Press
1911
[Transcriber's note: Page numbers in this book are indicated by numbers
enclosed in curly braces, e.g. {99}. They have been located where page
breaks occurred in the original book, in accordance with Project
Gutenberg's FAQ-V-99. In the HTML version of this book, page numbers
are placed in the left margin.]
{v}
PREFACE
The Syndics of the Cambridge University Press propose to issue a Nature
Study Series of which this is the first volume.
We count ourselves fortunate in securing Dr E. J. Russell as author and
Soil as subject. The subject is fundamental, for, just as the soil
lies beneath the plant and animal life we see, so is a knowledge of the
soil necessary for all understanding of flora and fauna. The real
complexity of the apparently simple element "Earth," and the variety of
methods required for exploring it, are typical of the problems which
the _tout ensemble_ of the outdoor world presents to the naturalist.
Dr E. J. Russell has not only acquired a first-rate and first-hand
knowledge of his subject at Wye and at Rothamsted; his own researches
have recently extended our knowledge of the micro-organisms in the soil
and their influence on fertility. Further, what is very much to our
purpose, he has himself had practical experience in teaching at an
elementary school in Wye and at a secondary school in Harpenden.
Just at the present moment, County Councils are trying to push rural
education and to awaken the intelligence of country children by
interesting them in their surroundings. It is, therefore, a favourable
opportunity to offer these pages as a concrete suggestion in model
lessons and object lessons, showing exactly what can be done under
existing conditions.
{vi}
The book is intended to help children to study nature; there is no
attempt to substitute book study for nature study. Hence, whilst there
are passages of continuous reading, it is not a mere "reader." Many
teachers, myself among them, have felt the difficulty of organising
practical work for large classes. Dr Russell has written so that,
whilst nominally showing the pupil how to learn, he is secretly
scattering hints for the teacher who is learning how to teach.
Abundant and varied practical exercises have been suggested, and
careful instructions have been given so that the book shall seem
intelligible even in the absence of a teacher. The proposed practical
work is not only what might be done by eager boys and girls on
half-holidays, but what can be done by every scholar in the course of
ordinary school work. The pictorial illustrations are intended as aids
to observation, not as substitutes. Drawing is one form of practical
exercise, and the preparation of corresponding illustrations in the
scholars' notebooks from the apparatus used in the classroom and the
fields around the school may afford exercises in artistic work with
pen, brush or camera.
Sufficient directions are given for the supply of necessary materials
and apparatus. The apparatus proposed is of the simplest character.
It is suggested that the book will be found most useful in the higher
standards of elementary schools, in preparatory schools and in the
lower forms of secondary schools, that is, where the ages of scholars
average from 12 to 14.
HUGH RICHARDSON
YORK, 7 January 1911
{vi}
CONTENTS
CHAP. PAGE
I. WHAT IS THE SOIL MADE OF? . . . . . . . . . . . . . 1
II. MORE ABOUT THE CLAY . . . . . . . . . . . . . . . . 9
III. WHAT LIME DOES TO CLAY . . . . . . . . . . . . . . . 19
IV. SOME EXPERIMENTS WITH THE SAND . . . . . . . . . . . 22
V. THE PART THAT BURNS AWAY . . . . . . . . . . . . . . 33
VI. THE PLANT FOOD IN THE SOIL . . . . . . . . . . . . . 41
VII. THE DWELLERS IN THE SOIL . . . . . . . . . . . . . . 53
VIII. THE SOIL AND THE PLANT . . . . . . . . . . . . . . . 64
IX. CULTIVATION AND TILLAGE . . . . . . . . . . . . . . 82
X. THE SOIL AND THE COUNTRYSIDE . . . . . . . . . . . . 100
XI. HOW SOIL HAS BEEN MADE . . . . . . . . . . . . . . . 116
APPENDIX . . . . . . . . . . . . . . . . . . . . . . 128
INDEX . . . . . . . . . . . . . . . . . . . . . . . 132
[Transcriber's note: The page numbers below are those in the original
book. However, in this e-book, to avoid the splitting of paragraphs,
the illustrations may have been moved to the page preceding or
following.]
LIST OF ILLUSTRATIONS
FIGURE PAGE
1. Soil and subsoil in St George's School garden . . . . 2
2. Columns showing what 100 parts of soil and subsoil
were made of . . . . . . . . . . . . . . . . . . . . 4
3. Columns showing what 100 parts of dried soil and
subsoil were made of . . . . . . . . . . . . . . . . 8
4. Clay shrinks when it dries . . . . . . . . . . . . . . 11
5. Clay swells up when it is placed in water . . . . . . 12
6. Landslip in the Isle of Wight.
_Phot._ Valentine & Son . . . . . . . . . . . . . . 13
7. Clay does not let water run through . . . . . . . . . 14
8. Sand allows air to pass through but clay does not . . 15
9. A brick allows both air and water to pass through it 17
10. Lime added to turbid clay water soon makes the clay
settle . . . . . . . . . . . . . . . . . . . . . . . 20
11. Sand dunes, Penhale, Cornwall.
_Phot._ Geological Survey . . . . . . . . . . . . . 23
12. Blowing sand covering up meadows and ruining them.
_Phot._ Geological Survey . . . . . . . . . . . . . 25
13. Model of a spring . . . . . . . . . . . . . . . . . . 26
14. Foot of chalk hill at Harpenden where a spring breaks
out. _Phot._ Lionel Armstrong . . . . . . . . . . . 27
15. The little pool and the spring.
_Phot._ Lionel Armstrong . . . . . . . . . . . . . . 28
16. Water spouting up from a bore hole, Old Cateriag
Quarry, Dunbar. _Phot._ Geological Survey . . . . . 29
17. Sandy soils in wet and in dry positions . . . . . . . 31
18. Map of the roads round Wye . . . . . . . . . . . . . . 32
19. Peat bog in Hoy, Orkney: peat is being cut for fuel.
_Phot._ Valentine & Son . . . . . . . . . . . . . . 39
20. Rye growing in surface soil, subsoil, and sand . . . . 42
21. Mustard growing in surface soil, subsoil, and sand . . 43
22. Mustard growing in soil previously cropped with rye,
and in soil previously uncropped . . . . . . . . . . 45
23. Pieces of grass, leaves, etc. change to plant food
in the surface soil lint not in the subsoil . . . . . 50
24. Soil in which earthworms have been living and making
burrows . . . . . . . . . . . . . . . . . . . . . . 55
25. Fresh soil turns milk bad, but baked soil does not . . 57
26. Soil contains tiny living things that grow on gelatine 58
27. Our breath makes lime water turn milky . . . . . . . . 59
28. Something in the soil uses up air and makes lime water
turn milky . . . . . . . . . . . . . . . . . . . . . 61
29. Soils are able to stick to water: clay or loam soils do
this better than sands . . . . . . . . . . . . . . . 65
30. Water can pass from wet to dry places in the soil, it
can even travel upwards . . . . . . . . . . . . . . 66
31. Plants growing in soils supplied from below with water.
All the water the plants get has to travel upwards 67
32. Mustard growing in soils supplied with varying
quantities of water . . . . . . . . . . . . . . . . 69
33. Wheat growing in moist and in dry soils . . . . . . . 71
34 _a_ and _b_. Plants found on a dry soil had
narrow leaves, those on a moist soil had wider
leaves. _Phot._ S. T. Parkinson . . . . . . . . . 72, 73
35. Plants give out water through their leaves . . . . . . 74
36. Stephen Hales's experiment in 1727 . . . . . . . . . . 75
37. Hill slope near Harpenden showing woodland at top and
arable land lower down. _Phot._ Lionel Armstrong 77
38. View further along the valley; woodland and arable
above, rough grassland near the river.
_Phot_. Lionel Armstrong . . . . . . . . . . . . . . 79
39. Rough grass pasture near the river. Higher up is
arable land. _Phot._ Lionel Armstrong . . . . . . . 81
40. After harvest the farmer breaks up his land with a
plough and then leaves it alone until seed time.
_Phot._ Lionel Armstrong . . . . . . . . . . . . . . 83
41. Rolling in mangold seed on the farm.
_Phot._ H. B. Hutchinson . . . . . . . . . . . . . . 85
42. Soil sampler . . . . . . . . . . . . . . . . . . . . . 88
43. Cultivation and mulching reduce the loss of water
from soils . . . . . . . . . . . . . . . . . . . . . 90
44 _a_ and _b_. Maize cannot compete successfully
with weeds . . . . . . . . . . . . . . . . . . . . 94, 95
45. A plot of wheat left untouched since 1882 at
Rothamsted has now become a dense thicket.
_Phot._ Lionel Armstrong . . . . . . . . . . . . . . 97
46. A badly drained wheat field . . . . . . . . . . . . . 99
47. Highly cultivated sandy soil in Kent . . . . . . . . . 103
48. A Surrey heath . . . . . . . . . . . . . . . . . . . . 105
49. Woodland and heather on high sandy land, Wimbledon
Common. _Phot._ R. H. Carter . . . . . . . . . . . 107
50. Poor sandy soil in Surrey, partly cultivated but mainly
wood and waste . . . . . . . . . . . . . . . . . . . 109
51. Open chalk cultivated country, Thanet . . . . . . . . 113
52. Cliffs at the seaside, Manorbier.
_Phot._ Geological Survey . . . . . . . . . . . . . 117
53. Cliffs in inland district, Arthur's Seat, Edinburgh.
_Phot._ Geological Survey . . . . . . . . . . . . . 119
54. Model of a stream . . . . . . . . . . . . . . . . . . 120
55. The bend of a river . . . . . . . . . . . . . . . . . 121
56. The winding river--the Stour at Wye.
_Phot._ R. H. Carter . . . . . . . . . . . . . . . . 123
57. Sketch map showing why Godmersham and Wye arose
where they did on the Stour . . . . . . . . . . . . 126
58. Ford at Coldharbour near Harpenden.
_Phot._ Lionel Armstrong . . . . . . . . . . . . . . 127
The photographs of the pot experiments are by Mr Lionel Armstrong.
{xi}
INTRODUCTION
The following pages contain the substance of lessons given at the
village school at Wye to the 4th, 5th, 6th and 7th standards (mixed)
and at St George's School, Harpenden, to the 3rd form. There is,
however, an important difference between the actual lessons and the
book. The lessons had reference to the soils round about the village,
and dealt mainly with local phenomena, general conclusions being only
sparingly drawn; while in the book it has been necessary to throw the
course into a more generalised form. The teacher in using the book
will have to reverse the process, he must find local illustrations and
make liberal use of them during the course; it is hoped that the
information given will help him over any difficulties he may experience.
This necessity for finding local illustrations constitutes one of the
fundamental differences between Nature Study subjects and other
subjects of the school curriculum. The textbooks in some of the others
may be necessary and sufficient; in Nature Study it is at most only
subsidiary, serving simply as a guide to the thing that is to be
studied; unless the thing itself be before the class it is no better
than a guide to a cathedral would be without the cathedral. And just
as the guide is successful only when he directs the attention of the
stranger to the important features of the place, and fails directly he
becomes garrulous and distracts attention, so a Nature Study book
succeeds {xii} only in as far as it helps in the study of the actual
thing, and fails if it is used passively and is substituted for an
active study. No description or illustration can take the place of
direct observation; the simplest thing in Nature is infinitely more
wonderful than our best word pictures can ever paint it.
The author recommends the teacher to look through the chapter before it
has to be taken in class and then to make a few expeditions in search
of local illustrations. It is not strictly necessary that the chapters
should be taken in the order given. The local phenomena must be dealt
with as they arise and as weather permits, or the opportunity may pass
not to return again during the course. In almost any lane, field, or
garden a sufficient number of illustrations may be obtained for our
purpose; if a stream and a hill are accessible the material is
practically complete, especially if the children can be induced to
pursue their studies during their summer holiday rambles. Of course
this entails a good deal of work for the teacher, but the results are
worth it. Children enjoy experimental and observation lessons in which
they take an active part and are not merely passive learners. The
value of such lessons in developing their latent powers and in
stimulating them to seek for knowledge in the great book of Nature is a
sufficient recompense to the enthusiastic teacher for the extra trouble
involved.
It is not desirable to work through a chapter in one lesson. Children
unaccustomed to make experiments or to see experiments done, will
probably require three or four lessons for getting through each of the
first few chapters, and two or three lessons for each of the others.
{xiii}
The pot experiments of Chaps. VI., VII. and VIII. should be started as
early in the course as possible. Twenty flower pots are wanted for the
set; they should be of the same size, about eight inches being a
convenient diameter, and should be kept together in a warm place.
Three are filled with sand, seven with subsoil, and the remaining ten
with surface soil. Three of the subsoil pots are uncropped, two being
stored moist and one dry. Four pots of the surface soil are uncropped
and moist, a fifth and sixth are uncropped and dry, one of these
contains earthworms (p. 54). Four glazed pots, e.g. large jam or
marmalade jars, are also wanted (p. 69). Mustard, buckwheat, or rye
make good crops, but many others will do. Leguminous crops, however,
show certain abnormal characters, while turnips and cabbages are apt to
fail: none of these should be used. It is highly desirable that the
pots should be duplicated.
The plots also should be started in the school garden as early as
convenient. Eight are required for the set: their treatment is
described in Chap. IX. Plots two yards square suffice.
A supply of sand, of clay, and of lime will be wanted, but it is not
necessary to have fresh material for each lesson. The sand may be
obtained from a builder, a sand pit, the sea shore or from a dealer in
chemical apparatus. The clay may be obtained from a brick yard; it
gives most satisfactory results after it has been ground ready for
brick making. Modelling clay is equally satisfactory. A supply of
rain water is desirable.
For a class of twelve children working in pairs at the experiments the
following apparatus is wanted for the whole course:--
{xiv}
Six tripods and bunsen burners or spirit lamps [2]
twelve pipe-clay triangles [4]
twelve crucibles or tin lids [3]
sixteen gas jars [4]
twelve beakers 250 c.c. capacity [4]
two beakers 500 c.c.
two beakers 100 c.c.
six egg-cups [2]
twelve funnels [3]
six funnel stands [1]
six perforated glass disks [3]
two tubulated bottles 500 c.c., four corks to fit
cork borers
4 lbs. assorted glass tubing
pestle and mortar
twelve Erlenmeyer flasks 50 c.c. [3]
six saucers
twelve flatbottomed flasks 100 c.c., six fitted with India
rubber stoppers bored with one hole [3], and six
with ordinary corks [3]
box as in Fig. 13
six glass tubes 1/2" diameter, 18" long [2]
six lamp chimneys [3]
six test tubes, corks to fit
three thermometers
soil sampler (p. 88)
balance and weights
two retort stands with rings and clamp.
The figures given in square brackets are the quantities that suffice
when the teacher alone does the experiments, it not being convenient
for the scholars to do much.
{xv}
In conclusion the author desires to tender his best thanks to the Rev.
Cecil Grant of St George's School, and to Mr W. J. Ashby of the Wye
School, for having allowed him the use of their schools and appliances
during the progress of these lessons. Especially are his thanks due to
Mr Lionel Armstrong for much help ungrudgingly rendered in collecting
material, taking photographs, and supervising the experiments.
E. J. R.
HARPENDEN,
February, 1911.
{1}
CHAPTER I
WHAT IS THE SOIL MADE OF?
Apparatus required.
_Soil and subsoil from a hole dug in the garden. Clay. Six tripods
and bunsen burners or spirit lamps [2]. Six crucibles or tin lids and
pipe-clay triangles [2]. Twelve glass jars or gas cylinders [4]. Six
beakers [2] [1]._
If we talk to a farmer or a gardener about soils he will say that there
are several kinds of soil; clay soils, gravel soils, peat soils, chalk
soils, and so on, and we may discover this for ourselves if we make
some rambles in the country and take careful notice of the ground about
us, particularly if we can leave the road and walk on the footpaths
across the fields. When we find the ground very hard in dry weather
and very sticky in wet weather we may be sure we are on a clay soil,
and may expect to find brick yards or tile works somewhere near, where
the clay is used. If the soil is loose, drying quickly after rain, and
if it can be scattered about by the hand like sand on the sea shore, we
know we are on a sandy soil and can look for pits where builder's sand
is dug. But it may very likely happen that the soil is something in
between, and that neither sand pits nor {2} clay pits can be found; if
we ask what sort of soil this is we are told it is a loam. A gravel
soil will be known at once by its gravel pits, and a chalk soil by the
white chalk quarries and old lime kilns, while a peat soil is black,
sometimes marshy and nearly always spongey to tread on.
[Illustration: Fig. 1. Soil and subsoil in St George's school garden]
We want to learn something of the soil round about us, and we will
begin by digging a hole about three feet deep to see what we can
discover. At Harpenden this is what the scholars saw:--the top eight
inches of soil was dark in colour and easy to dig; the soil below was
reddish brown in colour and very hard to dig; one changed into the
other so quickly that it was easy to see where the top soil ended and
the bottom soil began; no further change could, however, be seen below
the eight inch line. A drawing was made to show these things, and is
given in Fig. 1. You may find something quite different: sand, chalk,
or solid rock may occur below the soil, but you should enter whatever
you see into your notebooks and make a drawing, like Fig. 1, to be kept
for future use. Before filling in the hole some of the dark coloured
top soil, and some of the lighter coloured soil lying below (which is
called the subsoil), {3} should be taken for further examination; the
two samples should be kept separate and not mixed.
First look carefully at the top soil and rub some of it between your
fingers. We found that our sample was wet and therefore contained
water; it was very sticky like clay and therefore contained clay; there
were a few stones and some grit present and also some tiny pieces of
dead plants--roots, stems or leaves, but some so decayed that we could
not quite tell what they were. A few pieces of a soft white stone were
found that marked on the blackboard like chalk. Lastly, there were a
few fragments of coal and cinders, but as these were not a real part of
the soil we supposed they had got in by accident. The subsoil was also
wet and even more sticky than the top soil, it contained stones and
grit, but seemed almost free from plant remains and from the white
chalky fragments.
A few experiments will show how much of some of these things are
present. The amount of water may be discovered by weighing out ten
grams of soil, leaving it to dry in a warm place near the fire or in
the sun, and then weighing it again. In one experiment the results
were:--
Weight of top soil before drying ... 10 grams = 100 decigrams
" " " after " ... 8.3 " = 83 "
---- ---
Water lost ... 1.7 " = 17 "
A column 100 millimetres long was drawn to represent the 100 decigrams
of soil, and a mark was drawn 17 millimetres up to show the amount of
water (see Fig. 2).
Weight of bottom soil before drying ... 10 grams = 100 decigrams
" " " after " ... 8.7 " = 87 "
Water lost ... 1.3 " = 13 "
{4} Another column should be drawn for the subsoil. On drying the soil
it becomes lighter in colour and loses its stickiness, but it has not
permanently changed because as soon as water is added it comes back to
what it was before.
[Illustration: Fig. 2. Columns showing what 100 parts of soil and
subsoil were made of]
The dried lumps of soil are now to be broken up finely with a piece of
wood, but nothing must be lost. It is easy to see shrivelled pieces of
plant, but not easy to pick them out; the simplest plan is to burn them
away. The soil must be carefully tipped on to a tin lid, or into a
crucible, heated over a flame and stirred {5} with a long clean nail.
First of all it chars, then there is a little sparkling, but not much,
finally the soil turns red and does not change any further no matter
how much it is heated. The shade of red will at once be recognised as
brick red or terra cotta, indeed "terra cotta" means "baked earth."
When the soil is cold it should be examined again; it has become very
hard and the plant remains have either disappeared or have changed to
ash and crumble away directly they are touched. On weighing a further
loss is discovered, which was in our experiment:--
Weight of top soil after drying but before burning ... 83 decigrams
" " " " " " after " ... 76 "
--
The part that burnt away weighed ... 7 "
Weight of subsoil after drying but before burning ... 87 decigrams
" " " " " after " ... 84 "
--
The part that burnt away weighed ... 3 "
These results are entered on the column in Fig. 2.
The surface soil is seen to contain more material that will burn away
than the subsoil does. When the burnt soil is moistened it does not
become dark and sticky like it did before, it has completely changed
and cannot be made into soil again. It is more like brick dust than
soil.
For further experiments we shall want a fresh portion of the original
soil.
On a wet afternoon something was noticed that enabled us to get a
little further with our studies. The rain water ran down a sloping
piece of ground in a tiny channel it had made; the streamlet was very
muddy, and at first it was thought that all the soil was washed away.
But we soon saw that the channel was lined {6} with grit, some of which
was moving slowly down and some not at all. Grit can therefore be
separated from the rest of the soil by water.
This separation can be shown very well by the following experiment.
Rub ten grains of finely powdered soil with a little water (rain water
is better than tap water), and carefully pour the muddy liquid into a
large glass jar. Add more water to the rest of the soil, shake, and
again pour the liquid into the jar; go on doing this till the jar is
full. Then get some more jars and still keep on till the liquid is no
longer muddy but nearly clear. The part of the soil that remains
behind and will not float over into the jars is at once seen to be made
up of small stones, grit, and sand. Set the jars aside and look at
them after a day or so. The liquid remains muddy for some time, but
then it clears and a thick black sediment gathers at the bottom. If
now you very carefully pour the liquid off you can collect the
sediments: they are soft and sticky, and can be moulded into patterns
like clay. In order to see if they really contain clay we must do the
experiment again, but use pure clay from a brick yard, or modelling
clay, instead of soil. The muddy liquid is obtained as before, it
takes a long time to settle, but in the end it gives a sediment so much
like that from the soil, except in colour, that we shall be safe in
saying that the sediments in the jars contain the clay from the soil.
And thus we have been able to separate the sticky part of the soil--the
clay--from the gritty or sandy part which is not at all sticky. We may
even be able to find out something more. If we leave the soil sediment
and the clay sediment on separate tin lids to dry, and then examine
them carefully we may find that the {7} soil sediment is really a
little more gritty than the clay. Although it contains the clay it
also contains something else.
When the experiment is made very carefully in a proper way this
material can be separated from the pure clay. It is called silt, but
really there are a number of silts, some almost like clay and some
almost like sand; they shade one into the other.
If there is enough grit it should be weighed: we obtained 14 decigrams
of grit from 10 grams of our top soil and 17 decigrams from 10 grams of
bottom soil. We cannot separate the clay from the silt, but when this
is done in careful experiments it is found that the subsoil contains
more clay than the top soil. We should of course expect this because
we have found that the subsoil is more sticky than the top soil. These
results are put into the columns as before so that we can now see at
once how much of our soil is water, how much can burn away, how much is
grit, and how much is clay and other things.
What would have happened if the sample had been dug out during wetter
or drier weather? The quantity of water would have been different, but
in other respects the soil would have remained the same. It is
therefore best to avoid the changes in the amount of water by working
always with 10 grams of _dried_ soil. The results we obtained were:--
Top soil Subsoil
Weight of dry soil before burning ... 100 100 decigrams
" " " after " ... 92 97 "
--- ---
The part that burned away weighed ... 8 3
Weight of grit from 10 grams of dried soil 17 19 "
The columns are given in Fig. 3.
{8}
[Illustration: Fig. 3. Columns showing what 100 parts of dried soil
and subsoil were made of]
Summary. The experiments made so far have taught us these facts:--
1. Soil contains water, grit or sand, silt, clay, a part that burns
away, and some white chalky specks.
2. The top layer of soil to a depth of about eight inches is different
from the soil lying below, which is called the subsoil. It is less
sticky, easier to dig, and darker in colour. It contains more of the
material that burns away, but less clay than the subsoil.
3. When soil is dried it is not sticky but hard or crumbly; as soon as
it is moistened it changes back to what it was before. But when soil
is burnt it completely alters and can no longer be changed back again.
[1] See p. xiv for explanation of the figures in square brackets.
{9}