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The First Book of Farming
The First Book of Farming
By
CHARLES L. GOODRICH
Farmer
Expert in the Bureau of Plant Industry, United States Department of Agriculture, Washington, D.C.
Illustrated
GARDEN CITY NEW YORK DOUBLEDAY, PAGE & COMPANY 1923
1905, by DOUBLEDAY, PAGE & COMPANY PUBLISHED MARCH, 1905
PRINTED IN THE UNITED STATES AT THE COUNTRY LIFE PRESS, GARDEN CITY, N.Y.
PREFACE
The most successful farmers of the present day are those who work in harmony with the forces and laws of nature which control the growth and development of plants and animals. These men have gained their knowledge of those laws and forces by careful observation, experiment and study.
This book is a result of the author's search for these facts and truths as a student and farmer and his endeavor as a teacher to present them in a simple manner to others.
The object in presenting the book to the general public is the hope that it may be of assistance to farmers, students and teachers, in their search for the fundamental truths and principles of farming.
In the first part of the book an attempt has been made to select the most important and fundamental truths and principles underlying all agriculture and to present them in the order of their importance, beginning with the most important.
An endeavor has been made to present these truths to the reader and student in a simple and interesting manner. As far as possible each advance step is based on a previously stated fact or truth. A number of side truths are introduced at various places.
A number of simple experiments have been introduced into the text in the belief that they will make the work more interesting to the general reader, and will aid the student in learning to make simple investigations for himself.
The author recommends all who use the book to perform the experiments and to make the observations, and so come actively in touch with the work.
The observations begin on the farm. The author considers the plant the central and all-important factor or agent on the farm.
The root is regarded as the most important part of the plant to itself, and consequently to the plant grower.
The general truths or principles which state the conditions necessary for the growth and development of plant roots are regarded as the foundation truths or fundamental principles of all agriculture. These truths are as follows:
The roots of farm plants need for their best growth and development:
A firm, mellow soil.
A moist soil.
A ventilated soil.
A warm soil.
A soil supplied with plant food.
The first two chapters lead the reader quickly through logical reasoning to these fundamental truths, on which the remainder of the work is based.
A study of soils is made in connection with the root studies, as the two are so closely related.
After the study of roots and soils the other parts of the plant are considered in the order of their importance to the farmer or plant grower. The aim is always to get at fundamental facts and principles underlying all agricultural and horticultural practice.
The author regards the conditions necessary to root growth and development as the important factor constituting soil fertility, and in the last ten chapters takes up the discussion of certain farm operations and practices and their effects on these necessary conditions, and consequently their effect on the fertility of the soil.
The author extends gratitude to all who have in any way assisted in the preparation of this book, whether through advice, preparation of the text, preparation of the illustrations, or any other way in which he has received assistance.
C.L. GOODRICH.
GLENNDALE, Prince George Co., Maryland, January 21, 1905.
CONTENTS
PART I
GENERAL PRINCIPLES UNDERLYING PLANT CULTURE
Chapter Page
I.—INTRODUCTION TO PLANTS 3
II.—ROOTS 9 Uses of roots to plants 9 Habit of growth of roots 11 Conditions necessary for root growth 20
III.—SOILS 23 Relation of soil to plants 23 Classification of soils 26 How were soils made? 30 Soil texture 37
IV.—RELATION OF SOILS TO WATER 39 Importance of water to plants 39 Sources of soil water 40 Attitude of soils toward water: Percolation Absorption from below Power to hold water 40 The effect of working soils when wet 45
V.—FORMS OF SOIL WATER 48 Free water 48 Capillary water 49 Film water 50
VI.—LOSS OF SOIL WATER By surface wash By percolation and leaching By evaporation By transpiration How to check these losses 53
VII.—SOIL TEMPERATURE 57 How soils are warmed 58 How soils lose heat How to check loss of heat 59 Conditions which influence soil temperature 60 Value of organic matter 61
VIII.—PLANT FOOD IN THE SOIL 63
IX.—SEEDS 70 Conditions necessary for sprouting 70 Seed testing 75 How the seeds come up 77 Use of cotyledons and endosperm 79
X.—SEED PLANTING 81 Depth of planting: Operation of planting Planting machines 81 Seed classification 85 Transplanting 87
XI.—SPADING AND PLOWING 90 Spading the soil 90 Plowing 91 Why we spade and plow 91 Parts of a plow 92 Characteristics of a good plow 95 The furrow slice 96 How deep to plow 96 "Breaking out the middles" 97 Ridging the land 98 Time to plow 98 Bare fallow 100
XII.—HARROWING AND ROLLING 101 Harrowing: Why we harrow Time to harrow 101 Types of harrows 102 Rolling 106
XIII.—LEAVES 108 Facts about leaves 108 The uses of leaves to plants: Transpiration Starch making Digestion of food Conditions necessary for leaf work 109 How the work of leaves is interfered with 115
XIV.—STEMS 120 What are stems for? 120 How the work of the stem may be interfered with 126
XV.—FLOWERS 128 Function of flowers 128 Parts of flowers 129 Functions of the parts: Cross pollination 130 Value of a knowledge of the flowers 134 Fruit 136
PART II
SOIL FERTILITY AS AFFECTED BY FARM OPERATIONS AND FARM PRACTICES
Chapter Page
XVI.—A FERTILE SOIL 141 Physical properties: Power to absorb and hold water Power of ventilation Power to absorb and hold heat 142 Biological properties 143 Nitrogen-fixing germs 144 Nitrifying germs 145 Denitrifying germs 147 Chemical properties: Nitrogen in the soil Phosphoric acid in the soil Potash in the soil Lime in the soil Great importance of physical properties 147 Maintenance of fertility 150
XVII.—SOIL WATER 151 Importance of soil water 151 Necessity of soil water 151 Sources and forms of soil water 153 Too much water 154 Not enough water 154 Loss of soil water 155 How some farm operations influence soil water 156 Hoeing, raking, harrowing and cultivating 158 Manures and soil water 159 Methods of cropping and soil water 159 Selection of crops with reference to soil water 160
XVIII.—THE AFTER-CULTIVATION OF CROPS 164 Loss of water by evaporation 164 Loss of water through weeds 165 Saving the water 165 Time to cultivate 166 Tools for after-cultivation 167 Hilling and ridging 169
XIX.—FARM MANURES 171 The functions of manures and fertilizers 171 Classification 171 Importance of farm manures 172 Barn or stable manure 173 Loss of value 173 Checking the losses 176 Applying the manure to the soil 177 Proper condition of manure when applied 179 Composts 181
XX.—FARM MANURES, CONCLUDED 183 Green-crop manures: Functions 183 Benefits 185 Character of best plants for green-crop manuring 185 The time for green-manure crops 186 Leguminous green-manure crops 186 Non-leguminous green-manure plants 191
XXI.—COMMERCIAL FERTILIZERS 192 The raw materials 192 Sources of nitrogen 193 Sources of phosphoric acid 195 Sources of potash 199 Sources of lime 200
XXII.—COMMERCIAL FERTILIZERS, CONTINUED 202 Mixed fertilizers: What they are Many brands Safeguard for the farmer Low grade materials Inflating the guarantee 202 Valuation 205 Low grade mixtures 207 Buy on the plant food basis 209
XXIII.—COMMERCIAL FERTILIZERS, CONCLUDED 211 Home mixing of fertilizers 211 Kind and amount to buy 212 The crop 213 The soil 215 The system of farming 215 Testing the soil 215
XXIV.—ROTATION OF CROPS 219 Systems of cropping 219 The one crop system 221 Rotation of crops 224 Benefits derived from rotation of crops 230 The typical rotation 231 Conditions which modify the rotation 232 General rules 233 Length of rotation 233
XXV.—FARM DRAINAGE 235 How surplus water affects fertility 235 Indications of a need of drainage 235 Drains: Surface drains Open ditch drains Covered drains or under drains 236 Influence of covered drains on fertility 237 Location of drains: Grade Tile drains 238
GLOSSARY 241
LIST OF ILLUSTRATIONS
The farm equipment—plants, soils, animals, tools, buildings Frontispiece
Figure Facing Page
1. Specimen plants for study 6
2. The first effort of a sprouting seed 7
3. Germinating seeds with roots 7
4. To show that plant roots take water from the soil 10
5. To show that plant roots take food from the soil 10
6. A radish root, from which the stored food has been used to help produce a crop of seeds 11
7. A sweet-potato root producing new plants 11
8. Sweet-potato roots 14
9. Soy-bean roots 15
10. A plow stopped in the furrow, to show what it does to the roots of plants when used for after-cultivation 18
11. A corn-plant ten days after planting the seed 19
12. To show where growth in length of the root takes place 22
13. Radish seeds sprouted on dark cloth 22
14. To show how water gets into the roots of plants 23
15. To show osmose 23
16. To show that roots need air 26
17. Comparison of fresh and boiled water 26
18. Comparison of moist sand and puddled clay 27
19. Comparing soils 32
20. Water-test of soils 33
21. To show what becomes of the water taken from the soil by roots 40
22. Percolation experiment. To show the relative powers of soils to take in water falling on the surface 41
23. Bottles used in place of the lamp chimneys in Figs. 22 and 24 44
24. Capillarity of soils. To show the relative powers of soils to take water from below 44
25. Water-absorbing and water-holding powers of soils 45
26. Capillary tubes. To show how water rises in small tubes or is drawn into small spaces 48
27. Capillary plates 48
28. A cone of soil to show capillarity 49
29. To show the relative amounts of film-moisture held by coarse and fine soils 49
30. To show the effect of a soil mulch 56
31. Soil temperature experiment 57
32. Charts showing average temperature of a set of dry and wet soils during a period of five days 60
33. To show the value of organic matter 61
34. Soy-bean roots, showing nodules or tubercles 64
35. Garden-pea roots, showing tubercles or nodules 65
36. To show that seeds need water for germination 72
37. To show that seeds need air for germination 72
38. To show that seeds need air for germination 73
39. A seed-tester: two plates and a moist cloth 80
40. A seed-tester: a plaster cast with cavities in the surface for small seeds 80
41. Germinating corn-kernel and bean 81
42. To show how the bean-plant gets up 82
43. To show how the corn-plant gets out of the soil 82
44. To show the use of cotyledons 83
45. To show the use of the kernel to the young corn-plant 86
46. To show how deeply seeds should be planted 87
47. Operations of seed-planting 88
48. A collection of planting machines 89
49. Spading-fork and spade 92
50. A wood beam-plow 93
51. A slip-nose share and a slip-nose 96
52. A straight knife coulter 96
53. An iron beam-plow with rolling coulter and double clevis 96
54. A rolling cutter-harrow 97
55. Spring-toothed harrows 97
56. Spike-toothed harrows 104
57. A coulter-toothed harrow 104
58. A plank harrow 105
59. To show transpiration 108
60. Amount of transpiration 109
61. To show that growing leaves contain starch 114
62. To show that starch disappears from the leaf when the plant is placed in the dark 114
63. To show that sunlight is necessary for starch-making by leaves 115
64. To show that chlorophyl is necessary for starch formation in the leaf 115
65. To show the giving off of gas by leaves, and that sunlight is necessary for it 118
66. Seedling radishes reaching for light 119
67. Elm leaves injured by the "imported elm-tree leaf-beetle," a chewing insect 119
68. A horse-chestnut stem, showing leaves, buds, and scars, where last year's leaves dropped off 128
69. An underground stem. Buds show distinctly 129
70. Flower of cherry 130
71. Flower of apple 130
72. Pistil and stamen of flowering raspberry 131
73. Flower of buttercup 131
74. A magnolia flower showing central column of pistils and stamens 134
75. Flowers of squash 135
76. Flower of a lily 136
77. Bud and flower of jewel-weed or "touch-me-not" 137
78. Pistillate flower and perfect flower of strawberry 137
79. A crop of cowpeas 178
80. Red clover 179
81. Soy-beans in young orchard 182
82. A young alfalfa plant just coming into flower 183
83. Cross-sections of stone-drains 238
84. Cross-section of a pole-drain and of a tile-drain 238
85. A collection of drainage tools 239
86. A poorly laid tile-drain and a properly graded tile-drain 239
PART I
General Principles Underlying Plant Culture
THE FIRST BOOK OF FARMING
PART I
General Principles Underlying Plant Culture
CHAPTER I
INTRODUCTION TO PLANTS
Our object in reading and studying this book is to find out some facts that will help those of us who are thinking of going into farming and gardening as a business or recreation to start right, and will also help those of us that are already in the business to make our farms and gardens more productive.
In order to make the book of greatest value to you, I would urge you not only to read and study it, but also to make the excursions suggested and to perform the experiments. In other words, it will be of much greater value to you if you will make the observations and investigations and find out for yourselves the important facts and principles rather than simply take statements of the book unquestioned.
A very good time to begin this work is during the latter part of the summer, when the summer crops are ripening and the fall and winter crops are starting into growth. So suppose we begin our study with a visit to some farm in early September, to bring to mind the many things a farmer works with, the many things he has to think about and know about.
As we approach the farm we will probably see first the farm-house surrounded by shade trees, perhaps elms or maples, with the barns and other buildings grouped nearby. As we pass up the front walk we notice more or less lawn of neatly clipped grass, with flower beds bordering the walk, or we may find a number of chickens occupying the front yard, and the flower beds, placed in red half-barrels, set upon short posts. In the flower beds we may find petunias, nasturtiums, geraniums, rose bushes and other flowering plants. Going around the house, we come upon the dairy, with its rack of cans and pans set out for the daily sunning and airing. Nearby is a well with its oaken bucket; at the barn we find the farmer, and he very kindly consents to go with us to answer questions. In the barn and sheds we find wagons, plows, harrows, seed drills, hoes, rakes, scythes and many other tools and machines. Passing on to the fields, we go through the vegetable garden, where are carrots, parsnips, cabbages, beets, celery, sage and many other vegetables and herbs.
On the right, we see a field of corn just ready to harvest, and beyond a field of potatoes. On the left is the orchard, and we are invited to refresh ourselves with juicy apples. In the field beyond the hired man is plowing with a fine team of horses. In the South we would find a field of cotton and one of sweet potatoes, and perhaps sugar cane or peanuts. We have not failed to notice the pig weeds in the corn field nor the rag weed in the wheat stubble, and many other weeds and grasses in the fence corners.
Perhaps we may meet the cows coming from pasture to the stable. All the way we have been trampling on something very important which we will notice on our way back. In this field we find a coarse sandy soil, in the next one a soil that is finer and stiffer. The plow is turning up a reddish soil. In the garden we find the soil quite dark in color.
But these are only a few of the things we have found. If you have used your notebook you will discover that you have long lists of objects which you have noticed, and these may be grouped under the following headings: Animals, Plants, Soils, Buildings, Tools, etc.
The farmer, then, in his work on the farm deals with certain agents, chief among which are Soils, Plants, Animals, Tools and Buildings. Other agents which assist or retard his work according to circumstances are the air, sunlight, heat, moisture, plant food, microscopic organisms called bacteria, etc. These agents are controlled in their relations to one another by certain forces which work according to certain laws and principles of nature. To work intelligently and to obtain the best results the farmer must become familiar with these agents and must work in harmony with the laws and principles which control them.
Let us take up the study of some of these groups of agents, beginning with the most important or central one on the farm.
Which do you think is the most important group? Some will say "tools." The majority will probably say, study the soil first, "because we must work the soil before we can grow good crops." Some few will mention "plants." This last is right. The farm animals are dependent on plants for food. We till or work the soil to produce plants. Plants are living, growing things, and certain requirements or conditions are necessary for their growth and development; we cannot intelligently prepare the soil for plant growth until we know something about the work of plants and the conditions they need to do their work well.
For our first study of plants let us get together a number of farm and garden plants. Say, we have a corn plant, cotton, beet, turnip, carrot, onion, potato, grass, geranium, marigold, pigweed, thistle, or other farm or garden plants. In each case get the entire plant, with as much root as possible. Do these plants in any way resemble one another? All are green, all have roots, all have stems and leaves, some of them have flowers, fruit, and seeds, and the others in time will produce them.
Why does the farmer raise these plants? For food for man and animals; for clothing; for ornamental purposes; for pleasure, etc.
Which part of any or all of these farm plants is of greatest importance to the plant itself?
I am sure that you will agree that the root is the part most important to the plant itself, for if any part of a plant be separated from the root, that part ceases growth and will soon die, unless it is able to put out new roots. But the root from which the plant was cut will generally send up new shoots, unless it has nearly completed its life work. When a slip or cutting is placed in water or in moist sand it makes a root before it continues much in growth. When a seed is planted its first effort is to send a rootlet down into the soil.
Experiment to see if this is true by planting slips of willow, or geranium, or by planting corn or beans in a glass tumbler of soil, or in a box having a glass side, placing the seeds close to the glass; then watch and see what the seed does. Figs. 2 and 3.
Which of the parts of the plant is of greatest importance to the farmer or any plant grower, or to which part of a plant should the plant grower give his best attention? You will probably mention different parts of the different plants in answering this question. For instance, some will say, "The seed is the most important part of the wheat plant to the farmer, for that is what the wheat is grown for." "The fruit is the most important part of the apple plant for the same reason." "The leaves and grain of the corn, the leaves of the cabbage, are the important parts of these plants and should have the best attention of the grower, because they are the parts for which he grows the plants." But you must remember that all of these parts are dependent on the root for life and growth, as was brought out in the answer to the last question, and that if the farmer or plant grower desires a fine crop of leaves, stems, flowers, fruit or seeds, he must give his very best attention to the root. Judging from the poor way in which many farmers and plant growers prepare the soil for the plants they raise, and the poor way they care for the soil during the growth of the plants, they evidently think least of, and give least attention to, the roots of the plants.
Then, in studying our plants, which part shall we study first? Why, the roots, of course: To find out what they do for the plant, how they do this work, and what conditions are necessary for them to grow and to do their work well.
CHAPTER II
ROOTS
USES OF ROOTS TO PLANTS
Of what use are roots to plants, or, what work do they perform for the plants?
If the reader has ever tried to pull up weeds or other plants he will agree that one function of the roots of plants is to hold them firmly in place while they are growing.
Experiment.—Pull two plants from the soil, shake them free of earth, and place the roots of one in water and expose the roots of the other to the air. Notice that the plant whose roots are exposed to the air soon wilts, while the one whose roots were placed in water keeps fresh. You have noticed how a potted plant will wilt if the soil in the pot is allowed to become dry (see Fig. 4), or how the leaves of corn and other plants curl up and wither during long periods of dry weather. It is quite evident roots absorb moisture from the soil for the plant.
Experiment.—Plant some seeds in tumblers or in boxes filled with sand and in others filled with good garden soil. Keep them well watered and watch their progress for a few weeks (see Fig. 5). The plants in the garden soil will grow larger than those in the sand. The roots evidently must get food from the soil and those in the good garden soil get more than those in the poorer sand. Another important function of plant roots then is to take food from the soil for the plant.
You know how thick and fleshy the roots of radishes, beets and turnips are. Well, go into the garden and see if you can find a spring radish or an early turnip that has sent up a flower stalk, blossomed and produced seeds. If you are successful, cut the root in two and notice that instead of being hard and fleshy like the young radish or turnip, it has become hollow, or soft and spongy (see Fig. 6). Evidently the hard, fleshy young root was packed with food, which it afterwards gave up to produce flower stalk and seeds.
A fourth use of the root, then, is to store food for the future use of the plant.
Experiment.—Plant a sweet potato or place it with the lower end in a tumbler of water and set it in a warm room. Observe it from day to day as it puts out new shoots bearing leaves and roots (see Fig. 7). Break these off and plant them in soil and you have a number of new plants. If you can get the material, repeat this experiment with roots of horse-radish, raspberry, blackberry or dahlia. From this we see that it is the work of some roots to produce new plants. This function of roots is made use of in propagating or obtaining new plants of the sweet potato, horse-radish, blackberry, raspberry, dahlia and other plants.
We have now learned five important things that roots do for plants, namely:
Roots hold plants firmly in place.
They absorb water from the soil for the plants.
They absorb food from the soil for the plants.
Some roots store food for the future use of the plant.
Some roots produce new plants.
How do the roots do this work? To answer this question it will be necessary to study the habit of growth of the roots of our plants.
HABIT OF GROWTH OF ROOTS
The proper place to begin this study is in the field or garden. So we will make another excursion, and this time we will take with us a pick-axe or mattock, a shovel or two, a sharp stick, a quart or half-gallon pitcher, and several buckets of water. Arrived in the field, we will select a well-developed plant, say, of corn, potato or cotton. Then we will dig a hole about six feet long, three feet wide, and five or six feet deep, close to the plant, letting one side come about four or five inches from the base of the plant. It will be well to have this hole run across the row rather than lengthwise with it. Then with the pitcher pour water about the base of the plant and wash the soil away from the roots. Gently loosening the soil with the sharpened stick will hasten this work. In this way carefully expose the roots along the side of the hole, tracing them as far as possible laterally and as deep as possible, taking care to loosen them as little as possible from their natural position. (See Figs. 8 and 9.) Having exposed the roots of one kind of plant to a width and depth of five or six feet, expose the roots of six or eight plants of different kinds to a depth of about eighteen inches. As this may require more time than we can take for it in one day, it will be well to cover the exposed roots with some old burlaps or other material until we have them all ready, in order to keep them from drying and from injury.
When all is ready we will study the root system of each plant and answer these four questions:
In what part of the soil are most of the roots?
How deep do they penetrate the soil?
How near do they come to the surface of the soil?
How far do they reach out sidewise or laterally from the plant?
To the first question, "In what part of the soil are most of the roots?" you will give the following answers: "In the upper layer." "In the surface soil." "In the softer soil." "In the darker soil." "In the plowed soil."
These are all correct, but the last is the important one. Most of the roots will be formed in that part of the soil that has been plowed or spaded.
The second question, "How deep do the roots penetrate the soil?" is easily answered. Roots will be found penetrating the soil to depths of from two to six feet or more. (See Fig. 8.) The author has traced the roots of cowpea and soy bean plants to depths of five and six feet, corn roots four and five feet, parsnips over six feet. The sweet-potato roots illustrated in Fig. 8 penetrated the soil to a depth of over five feet. The roots of alfalfa or lucern have been traced to depths of from thirteen to sixteen feet or more.
How near to the surface of the soil do you find roots? Main side or lateral roots will be found within two or three inches of the surface, and little rootlets from these will be found reaching up as near the surface as there is a supply of moisture. After a continued period of wet weather, if the soil has not been disturbed, roots will be found coming to the very surface and even running along the top of the soil.
As to the fourth question, How far do roots reach out sidewise or laterally from the plant? you will find roots extending three, four, five and even six or more feet from the plant. They have numerous branches and rootlets, which fill all parts of the upper soil. Tree roots have been found thirty or forty feet in length.
We started on this observation lesson to find out something about the habit of growth of roots, so that we could tell how the roots do their work for the plant. But before going on with that question, let us stop right here and see whether we cannot find some very important lessons for the farmer and plant grower from what we have already seen. Is a knowledge of these facts we have learned about roots of any value to the farmer? Let us examine each case and see.
Of what value is it to the farmer to know that the larger part of the roots of farm plants develop in that part of the soil that has been plowed or spaded? It tells him that plowing tends to bring about the soil conditions which are favorable to the growth and development of roots. Therefore, the deeper he plows, the deeper is the body of the soil having conditions best suited for root growth, and the larger will be the crop which grows above the soil.
Of what value is it to the farmer to know that the roots of farm plants penetrate to depths of five or six feet in the soil? To answer this question it will be necessary for us to know something of the conditions necessary for root growth. So we will leave this till later.
Of what value is it to the farmer to know that many of the roots of his farm plants come very near the surface of the soil? It tells him that he should be careful in cultivating his crop to injure as few of these roots as possible. In some parts of the country, particularly in the South, the tool commonly used for field cultivation is a small plow. This is run alongside of the row, throwing the soil from the crop, and then again throwing the soil to the crop. Suppose we investigate, and see how this affects the roots of the crop.
Let us visit a field where some farmer is working a crop with a plow, or get him to do it, for the sake of the lesson. We will ask him to stop the plow somewhere opposite a plant, then we will dig a hole a little to one side of the plow and wash away the soil from over the plow (see Fig. 10), and see where the roots are. We will find that the plow-point runs under many strong-feeding lateral roots and tears them off, thus checking the feeding power of the plant, and consequently checking its growth. Now, if we can get a cultivator, we will have that run along the row and then wash away the loosened soil. It will be found that few, if any, of the main lateral roots have been injured.
Is it of any value to the farmer to know that roots extend laterally three to six feet and more on all sides of the plant, and that every part of the upper soil is filled with their branches and rootlets? This fact has a bearing on the application of manures and fertilizers. It tells the farmer that when he applies the manure and fertilizers to the soil he should mix the most of them thoroughly all through the soil, placing only a little directly in the row to start the young plant.
To find out how quickly the roots reach out into the soil, wash the soil away from some seedlings that have been growing only a few days, say, seven, ten and fifteen. (See Fig. 11.)
From our observations, then, we have learned the important lessons of deep, thorough plowing, careful shallow after-cultivation, and that fertilizers should be well mixed with the soil.
We are now ready to go back to our study of the habit of growth of roots, and can perhaps tell something of how the root does its work for the plant.
It is very easy to see how the roots hold the plant firmly in place, for they penetrate so thoroughly every part of the soil, and to such distances, that they hold with a grip that makes it impossible to remove the plant from the soil without tearing it free from the roots.
It is also on account of this very thorough reaching out through the soil that the roots are able to supply the plant with sufficient moisture and food.
We have doubtless observed that most of these roots are very slender and many very delicate. How did they manage to reach out into the soil so far from the plant? Or where does the root grow in length? To answer this question I will ask you to perform the following experiment:
Experiment.—Place some kernels of corn or other large seeds on a plate between the folds of a piece of wet cloth. Cover with a pane of glass or another plate. Keep the cloth moist till the seeds sprout and the young plants have roots two or three inches long. Now have at hand a plate, two pieces of glass, 4 by 6 inches, a piece of white cloth about 4 by 8 inches, a spool of dark thread, and two burnt matches, or small slivers of wood. A shallow tin pan may be used in place of the plate. Lay one pane of glass on the plate, letting one end rest in the bottom of the plate and the other on the opposite edge of the plate. At one end of the piece of cloth cut two slits on opposite sides about an inch down from the end and reaching nearly to the middle. Wet the cloth and spread it on the glass. Take one of the sprouted seeds, lay it on the cloth, tie pieces of thread around the main root at intervals of one-quarter inch from tip to seed. Tie carefully, so that the root will not be injured. Place the second pane of glass over the roots, letting the edge come just below the seed, slipping in the slivers of wood to prevent the glass crushing the roots. Wrap the two flaps of the cloth about the seed. Pour some water in the plate and leave for development. (Fig. 12.) A day or two of waiting will show conclusively that the lengthening takes place at the tip only, or just back of the tip. Is this fact of any value to the farmer? Yes. The soft tender root tips will force their way through a mellow soil with greater ease and rapidity than through a hard soil, and the more rapid the root growth the more rapid the development of the plant. This teaches us again the lesson of deep, thorough breaking and pulverizing of the soil before the crop is planted.
We have learned that the roots grow out into the soil in search of moisture and food, which they absorb for the use of the plant. How does the root take in moisture and food? Many people think that there are little mouths at the tips of the roots, and that the food and moisture are taken in through them. This is not so, for examination with the most powerful microscopes fails to discover any such mouths. Sprout seeds of radish, turnip or cabbage, or other seeds, on dark cloth, placed in plates and kept moist. Notice the fuzz or mass of root hairs near the ends of the tender roots of the seedlings (Fig. 13). Plant similar seed in sand or soil, and when they have started to grow pull them up and notice how difficult it is to remove all of the sand or dirt from the roots. This is because the delicate root hairs cling so closely to the soil grains. The root hairs are absorbing moisture laden with plant food from the surface of the soil particles. The root hairs are found only near the root tips. As the root grows older, its surface becomes tougher and harder, and the hairs die, while new ones appear on the new growth just back of the root tips, which are constantly reaching out after moisture and food. The moisture gets into the root hairs by a process called osmose. The following interesting experiment will give you an idea of this process or force of osmose.
Experiment.—Procure a wide-mouthed bottle, an egg, a glass tube about three inches long and a quarter-inch in diameter, a candle, and a piece of wire a little longer than the tube. Remove a part of the shell from the large end of the egg without breaking the skin beneath. This is easily done by gently tapping the shell with the handle of a pocket-knife until it is full of small cracks, and then, with the blade of the knife, picking off the small pieces. In this way remove the shell from the space about the size of a nickel. Remove the shell from the small end of the egg over a space about as large as the end of the glass tube. Next, from the lower end of the candle cut a piece about one-half inch long. Bore a hole in this just the size of the glass tube. Now soften one end of the piece of candle with the hole in it and stick it on to the small end of the egg so that the hole in the candle comes over the hole in the egg. Heat the wire, and with it solder the piece of candle more firmly to the egg, making a water-tight joint. Place the glass tube in the hole in the piece of candle, pushing it down till it touches the egg. Then, with the heated wire, solder the tube firmly in place. Now run the wire down the tube and break the skin of the egg just under the end of the tube. Fill the bottle with water till it overflows, and set the egg on the bottle, the large end in contact with the water (Fig. 14). In an hour or so the contents of the egg will be seen rising in the glass tube. This happens because the water is making its way by osmose into the egg through the skin, which has no openings, so far as can be discovered. If the bottle is kept supplied with water as fast as it is taken up by the egg, almost the entire contents of the egg will be forced out of the tube. In this way water in which plant food is dissolved enters the slender root hairs and rises through the plant.
Experiment.—This process of osmose may also be shown as follows (Fig. 15): Remove the shell from the large end of an egg without breaking the skin, break a hole in the small end of the egg and empty out the contents of the egg; rinse the shell with water. Fill a wide-mouthed bottle with water colored with a few drops of red ink. Fill the egg-shell partly full of clear water and set it on the bottle of colored water. Colored water will gradually pass through the membrane of the egg and color the water in the shell. Prepare another egg in the same way, but put colored water in the shell and clear water in the bottle. The colored water in the shell will pass through the skin and color the water in the bottle. Sugar or salt may be used in place of the red ink, and their presence after passing through the membrane may be detected by taste.
CONDITIONS NECESSARY FOR ROOT GROWTH
We have learned some of the things that the roots do for plants and a little about how the work is done. The next thing to find out is:
What conditions are necessary for the root to do its work?
We know that a part of the work of the root is to penetrate the soil and hold the plant firmly in place. Therefore, it needs a firm soil.
We know that the part of the root which penetrates the soil is tender and easily injured. Therefore, for rapid growth the root needs a mellow soil.
We know that part of the work of the root is to take moisture from the soil. Therefore, it needs a moist soil.
We know that part of the work of the root is to take food from the soil. Therefore, it needs a soil well supplied with plant food.
We know that roots stop their work in cold weather. Therefore, they need a warm soil.
Another condition needed by roots we will find out by experiment.
Experiment.—Take two wide-mouthed clear glass bottles (Fig. 16); fill one nearly full of water from the well or hydrant; fill the other bottle nearly full of water that has been boiled and cooled; place in each bottle a slip or cutting of Wandering Jew (called also inch plant, or tradescantia, and spiderwort), or some other plant that roots readily in water. Then pour on top of the boiled water about a quarter of an inch of oil—lard oil or cotton-seed oil or salad oil. This is to prevent the absorption of air. In a few days roots will appear on the slip in the hydrant water, while only a very few short ones, if any, will appear in the boiled water, and they will soon cease growing. Why is this? To answer this question, try another experiment. Take two bottles, filled as before, one with hydrant water and the other with boiled water; drop into each a slip of glass or a spoon or piece of metal long enough so that one end will rest on the bottom and the other against the side of the bottle, and let stand for an hour or so (Fig. 17). At the end of that time bubbles of air will be seen collecting on the glass or spoon in the hydrant water, but none in the boiled water. This shows us that water contains more or less air, and that boiling the water drives this air out. The cutting in the boiled water did not produce roots because there was no air in it and the oil kept it from absorbing any.
Experiment.—Into some tumblers of moist sand put cuttings of several kinds of plants that root readily (Fig. 18), geranium, tradescantia, begonia, etc. Put cuttings of same plants into tumblers filled with clay that has been wet and stirred very thoroughly, until it is about the consistency of cake batter. Keep the sand and puddled clay moist; do not allow the clay to crack, which it will do if it dries. The cuttings in the sand will strike root and grow, while most, if not all, those in the clay will soon die. The reason for this is that the sand is well ventilated and there is sufficient air for root development, while the clay is very poorly ventilated, and there is not sufficient air for root growth.
These experiments show us that to develop and do their work roots need air or a well-ventilated soil.
We have found the conditions which are necessary for the growth and development of plant roots, namely:
A firm, mellow soil.
A moist soil.
A soil supplied with available plant food.
A warm soil.
A ventilated soil.
These are the most important facts about plant growth so far as the plant grower is concerned. In other words, these conditions which are necessary for root growth and development are the most important truths of agriculture, or they are the foundation truths or principles upon which all agriculture is based. Having found these conditions, the next most important step is to find out how to bring them about in the soil, or, if they already exist, how to keep them or to improve them. This brings us, then, to a study of soils.
CHAPTER III
SOILS
The soil considered agriculturally, is that part of the earth's crust which is occupied by the roots of plants and from which they absorb food and moisture.
RELATION OF SOIL TO PLANTS
We have learned that plant roots penetrate the soil to hold the plant in a firm and stable position, to absorb moisture and with it plant food. We learned also that for roots to do these things well, the soil in which they grow must be mellow and firm, and must contain moisture and plant food, air must circulate in its pores and it must be warm.
How can we bring about these conditions? To answer this question intelligently it will be necessary for us to study the soil to find out something about its structure, its composition, its characteristics; also, how it was made and what forces or agencies were active in making it. Are these forces acting on the soil at the present time? Do they have any influence over the conditions which are favorable or unfavorable to plant growth? If so, can we control them in their action for the benefit or injury of plants?
We will begin this soil study with an excursion and a few experiments.
Go to the field. Examine the soil in the holes dug for the root lessons, noticing the difference between the upper or surface soil and the under or subsoil. Examine as many kinds of surface soils and subsoils as possible, also decayed leaf mould, the black soil of the woods, etc. If there are in the neighborhood any exposed embankments where a road has been cut through a hill, or where a river or the sea water has cut into a bank of soil, visit them and examine the exposed soils.
Experiment.—Place in separate pans, dishes, plates, boxes, or on boards, one or two pints each of sand, clay, decayed vegetable matter or leaf mould or woods soil, and garden soil. The soil should be fresh from the field. Examine the sand, clay and leaf mould, comparing them as to color; are they light or dark, are they moist or not? Test the soils for comparative size of particles by rubbing between the fingers (Fig. 19), noticing if they are coarse or fine, and for stickiness by squeezing in the hand and noting whether or not they easily crumble afterwards.
Experiment.—Take samples, about a teaspoonful, of sand, clay and leaf mould. Dry them and then place each in an iron spoon or on a small coal shovel and heat in stove to redness. It will be found that the leaf mould will smoke and burn, and will diminish in amount, while the sand and clay will not.
Experiment.—Take two wide-mouthed bottles; fill both nearly full of water. Into one put about a teaspoonful of clay and into the other the same amount of sand; shake both bottles thoroughly and set on table to settle (Fig. 20). It will be found that the sand settles very quickly and the clay very slowly.
As the result of our three experiments we will find something as follows:
Sand is light in color, moist, coarse, not sticky, settles quickly in water, and will not burn.
Clay is darker in color, moist, very fine, quite sticky, settles slowly in water, and will not burn.
Leaf mould or humus is very dark in color, moist, very fine, slightly sticky, and burns when placed in the fire.
Experiment.—We now have knowledge and means for making simple tests of soils. Repeat the last three experiments with the garden soil. We will find, perhaps, that it is dark in color and some of it burns away when placed in the fire, therefore it contains organic matter or decaying vegetable matter or humus, as it is called. This sample has perhaps fine particles and coarse particles; part of it will settle quickly in water while part settles very slowly, and it is sticky. Therefore we conclude that there are both clay and sand in it. If we shake a sample of it in a bottle of water and let it settle for several days, we can tell roughly from the layers of soil in the bottom of the bottle the relative amounts of sand and clay in the soil. Also if we weigh a sample before and after burning we can tell roughly the amount of organic matter in the soil. Test a number of soils and determine roughly the proportions of sand, clay and organic matter in them.
Experiment.—Take the pans of soil used in our first soil experiment and separate the soils in the pans into two parts by a trench across the centre on the pan. Now wet the soil in one side of the pan and stir it with a stick or a spoon, carefully smooth the surface of the soil in the other side of the pan and pour or sprinkle some water on it, but do not stir it. Set the pans aside till the soils are dry. This drying may take several days and in the meantime we will study the classification of soils.
CLASSIFICATION OF SOILS
Soil materials and soils are classified as follows:
Stones.—Coarse, irregular or rounded rock fragments or pieces of rock.
Gravel.—Coarse fragments and pebbles ranging in size from several inches in diameter down to 1/25 inch.
Sand.—Soil particles ranging from 1/25 of an inch down to 1/500 of an inch in diameter. Sand is divided into several grades or sizes.
Coarse sand 1/25 to 1/50 of an inch. Medium sand 1/50 to 1/100 of an inch. Fine sand 1/100 to 1/250 of an inch. Very fine sand 1/250 to 1/500 of an inch.
These grades of sand correspond very nearly with the grains of granulated and soft sugar and fine table salt.
Silt.—Fine soil particles ranging from 1/500 to 1/5000 of an inch in diameter. It feels very fine and smooth when rubbed between the fingers, especially when moist. A good illustration of silt is the silicon used for cleaning knives, a small amount of which can be obtained at most any grocery store. By rubbing some of this between the fingers, both dry and wet, one can get a fair idea of how a silty soil should feel. Silt when wet is sticky like clay.
Clay.—The finest of rock particles, 1/5000 to 1/250000 of an inch in diameter, too small to imagine. Clay when wet is very soft, slippery and very sticky. Yellow ochre and whiting from the paint shop are good illustrations of clay.
Humus, or decaying vegetable and animal matter. This is dark brown or almost black in color—decaying leaves and woods soil are examples.
Soils composed of the above materials:
Sands or Sandy Soils.—These soils are mixtures of the different grades of sand and small amounts of silt, clay and organic matter. They are light, loose and easy to work. They produce early crops, and are particularly adapted to early truck, fruit and bright tobacco, but are too light for general farm crops. To this class belongs the so-called Norfolk Sand. This is a coarse to medium, yellow or brown sand averaging about five-sixths sand and one-sixth silt and clay and is a typical early truck soil found all along the eastern coast of the United States.
"It is a mealy, porous, warm sand, well drained and easily cultivated. In regions where trucking forms an important part of agriculture, this soil is sought out as best adapted to the production of watermelons, canteloupes, sweet potatoes, early Irish potatoes, strawberries, early tomatoes, early peas, peppers, egg plant, rhubarb and even cabbage and cauliflower, though the latter crops produce better yields on a heavier soil."
A very similar sand in the central part of the country is called Miami Sand and, on the Pacific Coast, Fresno Sand. These names are given to these type soils by the Bureau of Soils of the United States Department of Agriculture.
Loams or Loamy Soils, consist of mixtures of the sands, silt and clay with some organic matter. The term loam is applied to a soil which, from its appearance in the field and the feeling when handled, appears to be about one-half sand and the other half silt and clay with more or less organic matter. These are naturally fine in texture and quite sticky when wet. They would be called clay by many on account of their stickiness. They are good soils for general farming and produce good grain, grass, corn, potatoes, cotton, vegetables, etc.
Sandy Loams, averaging about three-fifths sand and two-fifths silt and clay. These soils are tilled easily and are the lightest desirable soil for general farming. They are particularly adapted to corn and cotton and in some instances are used for small fruits and truck crops.
Silt Loam consists largely of silt with a small amount of sand, clay, and organic matter. These soils are some of the most difficult to till, but when well drained they are with careful management good general farming soils, producing good corn, wheat, oats, potatoes, alfalfa and fair cotton.
Clay Loams.—These soils contain more clay than the silt loams. They are stiff, sticky soils, and some of them are difficult to till. They are generally considered the strongest soils for general farming. They are particularly adapted to wheat, hay, corn and grass.
Gravelly loams are from one-fourth to two-thirds coarse grained; the remaining fine soil may be sandy loam, silt or clay loam. They are adapted to various crops according to the character of the fine soil. Some of them are best planted to fruit and forest.
Stony Loam.—Like the gravelly loam the stony loams are one-fourth to three-fourths sandy, silty or clay loam, the remainder being rock fragments of larger size than the gravel. These fragments are sometimes rough and irregular and sometimes rounded. The stones interfere seriously with tillage, and naturally the soils are best planted with forest or fruit.
Clay Soils.—Clay soils are mixtures of sand, silt, clay and humus, the clay existing in quite large quantities, there being a greater preponderance of the clay characteristics than in the clay loams; they are very heavy, sticky, and difficult to manage. Some clay soils are not worth farming. Those that can be profitably tilled are adapted to wheat, corn, hay and pasture.
Adobe Soils.—These are peculiar soils of the dry West. They are mixtures of clay, silt, some sand and large amounts of humus. Their peculiar characteristic is that they are very sticky when wet and bake very hard when dry and are, therefore, very difficult to manage, though they are generally very productive when they are moist enough to support crops.
Swamp Muck is a dark brown or black swamp soil consisting of large amounts of humus or decaying organic matter mixed with some fine sand and clay. It is found in low wet places.
Peat is also largely vegetable matter, consisting of tough roots, partially decayed leaves, moss, etc. It is quite dense and compact and in some regions is used for fuel.
HOW WERE SOILS MADE?
As a help in finding the answer to this question collect and examine a number of the following or similar specimens:
Brick.—Take pieces of brick and rub them together. A fine powder or dust will be the result.
Stones.—Rub together pieces of stone; the same result will follow, except that the dust will be finer and will be produced with greater difficulty because the stones are harder. Some stones will be found which will grind others without being much affected themselves.
Rock Salt or Cattle Salt.—This is a soft rock, easily broken. Place on a slate or platter one or two pieces about the size of an egg or the size of your fist. Slowly drop water on them till it runs down and partly covers the slate, then set away till the water dries up. Fine particles of salt will be found on the slate wherever the water ran and dried. This is because the water dissolved some of the rock.
Lime Stone.—This is harder. Crush two samples to a fine powder and place one in water and the other in vinegar. Water has apparently no effect on it, but small bubbles are seen to rise from the sample in vinegar. The vinegar which is a weak acid is slowly dissolving the rock. The chemists tell us water will also dissolve the limestone, but very slowly. There are large areas of soil which are the refuse from the dissolving of great masses of limestone.
We find that the rocks about us differ in hardness: they are ground to powder when rubbed together, some are easily dissolved in water, others are dissolved by weak acids.
Geologists tell us that the whole crust of the earth was at one time made up of rocks, part of which have been broken down into coarse and fine particles which form the gravel, sand and clay of our soils. The organic matter of our soils has been added by the decay of plants and animals. Several agencies have been active in this work of breaking down the rocks and making soils of them. If we look about we can perhaps see some of this work going on now.
Work of the Sun.—Examine a crockery plate or dish that has been many times in and out of a hot oven, noticing the little cracks all over its surface. Most substances expand when they are heated and contract when they are cooled. When the plate is placed in the oven the surface heats faster than the inner parts, and cools faster when taken out of the oven. The result is that there is unequal expansion and contraction in the plate and consequently tension or pulling of its parts against each other. The weaker part gives way and a crack appears. If hot water is put into a thick glass tumbler or bottle, the inner surface heats and expands faster than the outer parts and the result is tension and cracking. If cold water be poured on a warm bottle or piece of warm glass, it cracks, because there is unequal contraction. In the early part of a bright sunny afternoon feel of the surface of exposed rocks, bricks, boards, or buildings on which the sun has been shining. Examine them in the same way early the next morning. You will find that the rocks are heated by the sun just as the plate was heated when put into the oven, and when the sun goes down the rocks cool again. This causes tension in the rocks and little cracks and checks appear in them just as in the heated plate, only more slowly. This checking may also be brought about by a cool shower falling on the sun heated rocks just as the cool water cracked the warm glass. Many rocks if examined closely will be found to be composed of several materials. These materials do not expand and contract alike when heated and cooled and the tendency for them to check is greater even than that of the plate. This is the case with most rocks.
Work of Rain.—Rain falling on the rocks may dissolve a part of them just as it dissolved the rock salt; or, working into the small cracks made by the sun, may wash out loosened particles; or, during cold weather it may freeze in the cracks and by its expansion chip off small pieces; or, getting into large cracks and freezing, may split the rock just as freezing water splits a water pitcher or the water pipes.
Work of Moving Water.—Visit some neighboring beach or the banks of some rapid stream. See how the waves are rolling the sand and pebbles up and down the beach, grinding them together, rounding their corners and edges, throwing them up into sand beds, and carrying off the finer particles to deposit elsewhere. Now visit a quiet cove or inlet and see how the quiet water is laying down the fine particles, making a clay bed. Notice also how the water plants along the border are helping. They act as an immense strainer, collecting the suspended particles from the water, and with them and their bodies building beds of soil rich in organic matter or humus.
The sun, besides expanding and cracking the rocks by its heat, helps in another way to make soils. It warms the water that has been grinding soil on the beach or along the river banks and causes some of it to evaporate. This vapor rises, forms a cloud and floats away in the air. By and by the vapor forms into rain drops which may fall on the top of some mountain. These rain drops may wash loosened particles from the surface or crevices of exposed rocks. These drops are joined by others until, by and by, they form a little stream which carries its small burden of rock dust down the slope, now dropping some particles, now taking up others. Other little streams join this one until they form a brook which increases in size and power as it descends the mountain side. As it grows by the addition of other streams it picks up larger pieces, grinds them together, grinds at its banks and loads itself with rocks, pebbles, sand and clay. As the stream reaches the lower part of the mountain where the slope is less steep, it is checked in its course and the larger stones and pebbles are dropped while the sand and finer particles are carried on and deposited on the bottom of some broad quiet river farther down, and when the river overflows its banks, are distributed over the neighboring meadows, giving them a new coating of soil and often adding to their fertility. What a river does not leave along its course it carries out to sea to help build the sand bars and mud flats there. The rain drops have now gotten back to the beach where they take up again the work of grinding the soil.
The work of moving water can be seen in almost any road or cultivated field during or just after a rain, and particularly on the hillsides, where often the soil is loosened and carried from higher to lower parts, making barren sand and clay banks of fertile hillsides and destroying the fertility of the bottom lands below.
We have already noticed the work of freezing water in splitting small and large fragments from the rocks. Water moving over the surface of the earth in a solid form, or ice, was at an earlier period in the history of the earth one of the most powerful agencies in soil formation. Away up in Greenland and on the northern border of this continent the temperature is so low that most if not all of the moisture that falls on the earth falls as snow. This snow has piled up until it has become very deep and very heavy. The great weight has packed the bottom of this great snow bank to ice. On the mountains where the land was not level the masses of snow and ice, centuries ago, began to slide down the slopes and finally formed great rivers of solid water or moving ice.
The geologists tell us that at one time a great river of ice extended from the Arctic region as far south as central Pennsylvania and from New England to the Rocky Mountains. This vast river was very deep and very heavy and into its under surface were frozen sand, pebbles, larger stones and even great rocks. Thus it acted as a great rasp or file and did an immense amount of work grinding rocks and making soils. It ground down mountains and carried great beds of soil from one place to another. When this great ice river melted, it dropped its load of rocks and soils, and as a result we find in that region of the country great boulders and beds of sand and clay scattered over the land.
Work of the Air.—The air has helped in the work of wearing down the rocks and making soils. If a piece of iron be exposed to moist air a part of the air unites with part of the iron and forms iron rust. In the same way when moist air comes in contact with some rocks part of the air unites with part of the rock and forms rock rust which crumbles off or is washed away by water. Thus the air helps to break down the rocks. Moving air or wind picks up dust particles and carries them from one field to another. On sandy beaches the wind often blows the sand along like snow and piles it into drifts. The entire surface of sandy regions is sometimes changed in this way. Sands blown from deserts sometimes bury forests which with their foliage sift the fatal winding sheet from the dust-laden winds.
The Work of Plants.—Living plants sometimes send their roots into rock crevices; there they grow, expand, and split off rock fragments. Certain kinds of plants live on the surface of rocks. They feed on the rocks and when they die and decay they keep the surface of the rocks moist and also produce carbonic acid which dissolves the rocks slowly just as the vinegar dissolved the limestone in our experiment.
Dead decaying roots, stems, and leaves of plants form largely the organic matter of the soil. When organic matter has undergone a certain amount of decay it is called humus, and these soils are called organic soils or humus soils. The black soils of the woods, swamps and prairies, contain large amounts of humus.
Work of Animals.—Earth worms and the larvae of insects which burrow in the soil eat soil particles which pass through their bodies and are partially dissolved. These particles are generally cast out on the surface of the soil. Thus these little animals help to move soil, to dissolve soil, and to open up passages for the entrance of air and rain.
SOIL TEXTURE
We have seen that the soil particles vary in size and that for the best development of the plant the particles of the soil must be so arranged that the delicate rootlets can readily push their way about in search of food, or, in other words, that the soil must have a certain texture. By the texture of the soil we mean the size of its particles and their relation to each other. The following terms are used in describing soil textures: Coarse, fine, open, close, loose, hard, stiff, compact, soft, mellow, porous, leachy, retentive, cloddy, lumpy, light, heavy. Which of these terms will apply to the texture of sand, which to clay, which to humus, which to the garden soil, which to a soil that plant roots can easily penetrate? We find then that texture of the soil depends largely on the relative amounts of sand, silt, clay and humus that it contains.
CHAPTER IV
RELATION OF SOILS TO WATER
IMPORTANCE OF WATER TO PLANTS
We learned in a previous paragraph that plant roots take moisture from the soil. What becomes of this moisture? We will answer this question with an experiment.
Experiment.—Take a pot or tumbler in which a young plant is growing, also a piece of pasteboard large enough to cover the top of the pot or tumbler; cut a slit from the edge to the centre of the board, then place it on top of the pot, letting the stem of the plant enter the slit. Now close the slit with wax or tallow, making it perfectly tight about the stem. If the plant is not too large invert a tumbler over it (Fig. 21), letting the edge of the tumbler rest on the pasteboard; if a tumbler is not large enough use a glass jar. Place in a sunny window. Moisture will be seen collecting on the inner surface of the glass. Where does this come from? It is absorbed from the soil by the roots of the plant and is sent with its load of dissolved plant food up through the stem to the leaves. There most of the moisture is passed from the leaves to the air and some of it is condensed on the side of the glass.
By experiments at the Cornell University Agricultural Experiment Station, Ithaca, N.Y., it has been found that during the growth of a sixty bushel crop of corn the plants pump from the soil by means of their roots, and send into the air through their leaves over nine hundred tons of water. A twenty-five bushel crop of wheat uses over five hundred tons of water in the same way. This gives us some idea of the importance of water to the plant and the necessity of knowing something of the power of the soil to absorb and hold moisture for the use of the plant. Also the importance of knowing if we can in any way control or influence the water-holding power of the soil for the good of the plant.
SOURCES OF SOIL WATER
From what sources does the soil receive water? From the air above, in the form of rain, dew, hail and snow, falling on the surface, and from the lower soil. This water enters the soil more or less rapidly.
ATTITUDE OF THE SOILS TOWARDS WATER
Which soils have the greater power to take in the rain which falls on their surface?
Experiment.—Take four student-lamp chimneys. (In case the chimneys cannot be found get some slender bottles like salad oil bottles or wine bottles and cut the bottoms off with a hot rod. While the rod is heating make a shallow notch in the glass with the wet corner of a file in the direction you wish to make the cut. When the rod is hot lay the end of it lengthwise on the notch. Very soon a little crack will be seen to start from the notch. Lead this crack around the bottle with the hot rod and the bottom of the bottle will drop off.) (Fig. 23.) Make a rack to hold them. Tie a piece of cheese cloth or other thin cloth over the small ends of the chimneys. Then fill them nearly full respectively, of dry, sifted, coarse sand, clay, humus soil, and garden soil. Place them in the rack; place under them a pan or dish. Pour water in the upper ends of the tubes until it soaks through and drips from the lower end (Fig. 22). Ordinary sunburner lamp chimneys may be used for the experiment by tying the cloth over the tops; then invert them, fill them with soil and set in plates or pans. The sand will take the water in and let it run through quickly; the clay is very slow to take it in and let it run through; the humus soil takes the water in quite readily. Repeat the experiment with one of the soils, packing the soil tightly in one tube and leaving it loose in another. The water will be found to penetrate the loose soil more rapidly than the packed soil. We see then that the power of the soil to take in rainfall depends on its texture or the size and compactness of the particles.
If the soil of our farm is largely clay, what happens to the rain that falls on it? The clay takes the water in so slowly that most of it runs off and is lost. Very likely it carries with it some of the surface soil which it has soaked and loosened, and thus leaves the farm washed and gullied.
What can we do for our clay soils to help them to absorb the rain more rapidly? For immediate results we can plow them and keep them loose and open with the tillage tools. For more permanent results we may mix sand with them, but sand is not always to be obtained and is expensive to haul. The best method is to mix organic matter with them by plowing in stable manures, or woods soil, or decayed leaves, or by growing crops and turning them under. The organic matter not only loosens the soil but also adds plant food to it, and during its decay produces carbonic acid which helps to dissolve the mineral matter and make available the plant food that is in it.
Clay soils can also be made loose and open by applying lime to them.
Experiment.—Take two bottles or jars, put therein a few spoonsful of clay soil, fill with water, put a little lime in one of them, shake both and set them on the table. It will be noticed that the clay in the bottle containing lime settles in flakes or crumbs, and much faster than in the other bottle. In the same manner, lime applied to a field of clay has a tendency to collect the very fine particles of soil into flakes or crumbs and give it somewhat the open texture of a sandy soil. Lime is applied to soil for this purpose at the rate of twenty bushels per acre once in four or five years.
Which soils have the greater power to absorb or pump moisture from below?
Experiment.—Use the same or a similar set of tubes as in the experiment illustrated in Fig. 23. Fill the tubes with the same kinds of dry sifted soils. Then pour water into the pan or dish beneath the tubes until it rises a quarter of an inch above the lower end of the tubes (Fig. 24). Watch the water rise in the soils. The water will be found to rise rapidly in the sand about two or three inches and then stop or continue very slowly a short distance further. In the clay it starts very slowly, but after several hours is finally carried to the top of the soil. The organic matter takes it up less rapidly than the sand, faster than the clay, and finally carries it to the top. By this and further experiments it will be found that the power of soils to take moisture from below depends on their texture or the size and closeness of their particles.
We found the sand pumped the water only a short distance and then stopped.
What can we do for our sandy soils to give them greater power to take moisture from below? For immediate results we can compact them by rolling or packing. This brings the particles closer together, makes the spaces between them smaller, and therefore allows the water to climb higher. For more lasting results we can fill them with organic matter in the shape of stable manures or crops turned under. Clay may be used, but is expensive to haul.
Which soils have greatest power to hold the water which enters them?
Experiment.—Use the same or similar apparatus as for the last experiment. After placing the cloth caps over the ends of the tubes label and carefully weigh each one, keeping a record of each; then fill them with the dry soils and weigh again. Now place the tubes in the rack and pour water in the upper ends until the entire soil is wet; cover the tops and allow the surplus water to drain out; when the dripping stops, weigh the tubes again, and by subtraction find the amount of water held by the soil in each tube; compute the percentage. It will be found that the organic matter will hold a much larger percentage of water than the other soils; and the clay more than the sand. The tube of organic soil will actually hold a larger amount of water than the other tubes. (See also Fig. 25.)
In the experiment on page 40 we noticed that the sand took in the water poured on its surface and let it run through very quickly. This is a fault of sandy soils.
What can we do for our sandy soils to help them to hold better the moisture which falls on them and tends to leach through them? For immediate effect we can close the pores somewhat by compacting the soil with the roller. For more lasting effects, we can fill them with organic matter.
Which soils will hold longest the water which they have absorbed? Or which soils will keep moist longest in dry weather?
Experiment.—Fill a pan or bucket with moist sand, another with moist clay, and a third with moist organic matter; set them in the sun to dry and notice which dries last. The organic matter will be found to hold moisture much longer than the other soils. The power of the other soils to hold moisture through dry weather can be improved by mixing organic matter with them.
We find then that the power of soils to absorb and hold moisture depends on the amount of sand, clay, or humus which they contain, and the compactness of the particles. We see also how useful organic matter is in improving sandy and clayey soils.
THE EFFECT OF WORKING SOILS WHEN WET
By this time the soils we left in the pans (see page 26), sand, clay, humus and garden soil, must be dry. If so, examine them. We find that the clay which was stirred when wet has dried into an almost bricklike mass, while that which was not stirred is not so hard, though it has a thick, hard crust. The sand is not much affected by stirring when wet. The organic matter which was stirred when wet has perhaps stiffened a little, but very easily crumbles; the unstirred part was not much affected by the wetting and drying.
The garden soil after drying is not as stiff as the clay nor as loose as the sand and humus. This is because it is very likely a mixture of all three, the sand and the humus checking the baking. This teaches us that it is not a good plan to work soils when they are wet if they are stiff and sticky; and that our stiff clay soils can be kept from drying hard or baking by the use of organic matter. "And that's a witness" for organic matter.
The relation of the soil to moisture is very important, for moisture is one of the greatest factors if not the greatest in the growth of the crop.
The power to absorb or soak up moisture from any source is greatest in those soils whose particles are smaller and fit closer together.
It is for this reason that strong loams and clay soils absorb and hold three times as much water as sandy soils do, while peaty or humus soils absorb a still larger proportion.
The reason why crops burn up so quickly on sandy soils during dry seasons is because of their weak power to hold water.
The clay and humus soils carry crops through dry weather better because of their power to hold moisture and to absorb or soak up moisture from below. It is for this reason also that clay and peaty soils more often need draining than sandy soils.
When rain falls on a sandy soil it enters readily, but it is apt to pass rapidly down and be, to a great extent, lost in the subsoil, for the sand has not sufficient power to hold much of it.
When rain falls on a clay soil it enters less readily because of the closeness of the particles, and during long rains or heavy showers some of the water may run off the surface. If the surface has been recently broken and softened with the plow or cultivator the rain enters more readily. What does enter is held and is not allowed to run through as in the case of the sand.
Humus soil absorbs the rain as readily as the sand and holds it with a firmer grip than clay.
This fact gives us a hint as to how we may improve the sand and clay.
Organic matter mixed with these soils by applying manures or plowing under green crops will cause the sand to hold the rain better and the clay to absorb it more readily.
CHAPTER V
FORMS OF SOIL WATER
Water which comes to the soil and is absorbed exists in the soil principally in two forms: Free water and capillary water.
FREE WATER
Free water is that form of water which fills our wells, is found in the bottoms of holes dug in the ground during wet seasons and is often found standing on the surface of the soil after heavy or long continued rains. It is sometimes called ground water or standing water and flows under the influence of gravity.
Is free water good for the roots of farm plants? If we remember how the root takes its food and moisture, namely through the delicate root hairs; and also remember the experiment which showed us that roots need air, we can readily see that free water would give the root hairs enough moisture, but it would at the same time drown them by cutting off the air. Therefore free water is not directly useful to the roots of house plants or farm plants, excepting such as are naturally swamp plants, like rice, which grows part of the time with its roots covered with free water.
CAPILLARY WATER
If you will take a number of glass tubes of different sizes, the largest not more than one-fourth of an inch in diameter, and hold them with one end of each in water or some colored liquid, you will notice that the water rises in the tubes (Fig. 26), and that it rises highest in the smallest tube. The force which causes the water to rise in these tubes is called the capillary force, from the old Latin word capillum (a hair), because it is most marked in hair-like tubes, the smaller the tube the higher the water will rise. The water which rises in the tubes is called capillary water.
Another method of illustrating capillary water is to tie or hold together two flat pieces of glass, keeping two of the edges close together and separating the opposite two about one-eighth of an inch with a sliver of wood. Then set them in a plate of water or colored liquid and notice how the water rises between the pieces of glass, rising higher the smaller the space (Fig. 27). It is the capillary force which causes water to rise in a piece of cloth or paper dipped in water.
Take a plate and pour onto it a cone-shaped pile of dry sand or fine soil; then pour water around the base of the pile and note how the water is drawn up into the soil by capillary force (Fig. 28).
Capillary water is the other important form of water in the soil. This is moisture which is drawn by capillary force or soaks into the spaces between the soil particles and covers each particle with a thin film of moisture.
FILM WATER
Take a marble or a pebble, dip it into water and notice the thin layer or film of water that clings to it. This is a form of capillary water and is sometimes called film water or film moisture. Take a handful of soil that is moist but not wet, notice that it does not wet the hand, and yet there is moisture all through it; each particle is covered with a very thin film of water.
Now this film water is just the form of water that can supply the very slender root hairs without drowning them, that is, without keeping the air from them. And the plant grower should see to it that the roots of his plants are well supplied with film water and are not drowned by the presence of free water. Capillary water may sometimes completely fill the spaces between the soil particles; when this occurs the roots are drowned just as in the case of free water as we saw when cuttings were placed in the puddled clay (see Fig. 18). Free water is indirectly of use to the plant because it serves as a supply for capillary and film moisture.
Now I think we can answer the question which was asked when we were studying the habit of growth of roots but was left unanswered at the time (see page 14). The question was this: Of what value is it to the farmer to know that roots enter the soil to a depth of three to six feet? We know that roots will not grow without air. We also know that if the soil is full of free water there is no air in it, and, therefore, roots of most plants will not grow in it. It is, therefore, of interest to the farmer to see that free water does not come within at least three or four feet of the surface of the soil so that the roots of his crops may have plenty of well ventilated soil in which to develop. If there is a tendency for free water to fill the soil a large part of the time, the farmer can get rid of it by draining the land. We get here a lesson for the grower of house plants also. It is that we must be careful that the soil in the pots or boxes in which our plants are growing is always supplied with film water and not wet and soggy with free water. Water should not be left standing long in the saucer under the pot of a growing plant. It is best to water the pot from the top and let the surplus water drain into the saucer and then empty it out.
Which soils have the greatest capacity for film water?
Experiment.—Place in a tumbler or bottle one-half pound of pebbles about the size of a pea or bean; pour a few drops of water on them and shake them; continue adding water and shaking them till every pebble is covered with a film of water; let any surplus water drain off. Then weigh again; the difference in the two weights will be approximately the weight of the film water that the pebbles can carry. Repeat this with sand and compare the two amounts of water. A striking illustration can be made by taking two slender bottles and placing in them amounts of colored water equal to the amounts of film water held by the pebbles and sand respectively. In the accompanying illustration (Fig. 29), A represents the amount of water that was found necessary to cover the pebbles in tumbler B with a film of moisture. C is the amount that was necessary to cover with a film the particles of sand in D. The finer soil has the greater area for film moisture. It has been estimated that the particles of a cubic foot of clay loam have a possible aggregate film surface of three-fourths of an acre.
CHAPTER VI
LOSS OF SOIL WATER
LOSS OF SOIL WATER AND MEANS OF CHECKING THE LOSS
We noticed in previous paragraphs that soil might at times have too much water in it for proper ventilation and so check the growth of the roots of the plant. Now is it possible that soil water may be lost or wasted and if so can we check the loss?
In the experiment to find out how well the soils would take in the rainfall (page 40) we noticed that the clay soil took in the water very slowly and that on a field of clay soil part of the rain water would be likely to run off over the surface and be lost. Free water may be lost then, by surface wash.
We noticed methods of checking this loss, namely, pulverizing the soil with the tillage tools and putting organic matter into it to make it absorb the rain more readily.
We noticed that water poured on the sand ran through it very quickly and was apt to be lost by leaching or percolation. This we found could be checked by rolling the soil and by putting organic matter into it to close the pores.
We learned that roots take water from the soil for the use of the plant and send it up to the leaves, which in turn send it out into the air, or transpire it, as this process is called. We learned also that the amount transpired is very great. Now water that is pumped up and transpired by the crops we are growing we consider properly used. But when weeds grow with the crop and pump and transpire water we consider this water as lost or wasted.
Water may be lost then by being pumped up and transpired by weeds. And this is the way weeds do their greatest injury to crops during dry weather. The remedy is easily pointed out. Kill the weeds or do not let them get a start.
There is another way, which we are not apt to notice, by which water may be lost from the soil. When the soil in the pans in a previous experiment (page 26) had been wet and set aside a few days it became very dry. How did the water get out of this soil? That at the surface of the soil evaporated or was changed into vapor and passed into the air. Then water from below the surface was pumped up by capillary force to take its place just as the water was pumped up in the tubes of soil. This in turn was evaporated and the process repeated till all of the water in the soil had passed into the air. Now this process is going on in the field whenever it is not raining or the ground is not frozen very hard.
Water then may be lost by evaporation.
How can we check this loss?
Suppose we try the experiment of covering the soil with some material that cannot pump water readily.
Experiment.—Take four glass fruit jars, two-quart size, with straight sides. If you cannot get them with straight sides cut off the tops with a hot iron just below the shoulder; tin pails will do if the glass jars cannot be had. Fill these with moist soil from the field or garden, packing it till it is as hard as the unplowed or unspaded soil. Leave one of them in this condition; from two of them remove an inch or two of soil and replace it in the case of one with clean, dry, coarse sand, and in the case of the other with chaff or straw cut into half-inch lengths. Stir the soil in the fourth one to a depth of one inch, leaving it light and crumbly. Now weigh the jars and set them aside. Weigh each day for several days. The four jars illustrated in Fig. 30 were prepared in this way and allowed to stand seven days. In that time they lost the following amounts of water:
Amounts of water lost from jars of prepared soil in seven days.
No. 1 packed soil—lost 5.5 oz. equal to about 75 tons per acre.
No. 2 covered with straw—lost 2 oz. equal to about 27 tons per acre.
No. 3 covered with dry sand—lost 0 oz. equal to about tons per acre.
No. 4 covered with crumbled soil—lost 2.5 oz., equal to about 34 tons per acre.
Why did not 2, 3 and 4 lose as much water as No. 1?
The soil in jar No. 1 was packed and water was pumped to the surface by capillary force and was evaporated as fast as it came to the surface.
In No. 2 the water could rise rapidly until it reached the straw, then it was stopped almost entirely. But the straw being coarse, the air circulated in it more or less freely and there was a slow loss by evaporation. In jar No. 3 the water could rise only to the sand, which was so coarse that the water could not climb on it to the surface, and the air circulated in the sand so slowly that there was not sufficient evaporation to affect scales weighing to one-quarter ounce. No. 4 lost less than No. 1 because, as in the case of the sand, the water could not climb rapidly to the surface on the coarse crumbs of soil. The loss that did take place from No. 4 was what the air took from the loosely stirred soil on the surface with a very little from the lower soil. Simply stirring the surface of the sod in No. 4 reduced the loss of water to less than half the loss from the hard soil in No. 1.
This experiment gives us the clew to the method of checking loss of water from the soil by evaporation. It is to keep the water from climbing up to the surface, or check the power of the soil to pump the water to the surface by making it loose on top. This loose soil is called a soil mulch. Everything that we do to the soil that loosens and crumbles the surface tends to check the loss of water by evaporation from the soil below.
CHAPTER VII
SOIL TEMPERATURE
We learned that roots need heat for their growth and development. Now what is the relation of the different kinds of soil toward heat or what are their relative powers to absorb and hold heat?
Experiment.—Some days before this experiment, spread on a dry floor about a half bushel each of sand, clay and decayed leaf mould or black woods soil. Stir them occasionally till they are thoroughly dry. When they are dry place them separately in three boxes or large flower pots and keep dry. In three similar boxes or pots place wet sand, wet clay, and wet humus. Place a thermometer in each of the soils, placing the bulb between one and two inches below the surface (Fig. 31). Then place the soils out of doors where the sun can shine on them and leave them several days. If a rain should come up protect the dry soils. Observe and make a record of the temperatures of each soil several times a day. Chart the average of several days observations. Fig. 32 shows the averages of several days observations on a certain set of soils.
It will be noticed that the temperature of the soils increased until the early part of the afternoon and after that time they lost heat.
HOW SOILS ARE WARMED
Experiment.—Hold your hand in bright sunlight or near a warm stove or radiator. Your hand is warmed by heat radiated from the sun or warm stove through the air to your body. In the same manner the rays of the sun heat the surface of the soil.
Experiment.—Take the stove poker or any small iron rod and hold one end of it in the fire or hold one end of a piece of wire in a candle or lamp flame. The end of the rod or wire will quickly become very hot and heat will gradually be carried its entire length until it becomes too hot to hold. This carrying of the heat from particle to particle through the length of the rod is called heating by conduction. Now when the warm rays of the sun reach the soil, or a warm wind blows over it, the surface particles are warmed and then pass the heat on to the next ones below, and these in turn pass it to others and so on till the soil becomes heated to a considerable depth by conduction.
A clay soil will absorb heat by conduction faster than a sandy soil because the particles of the clay lie so close together that the heat passes more readily from one to another than in the case of the coarser sand.
If the soil is open and porous, warm air and warm rains can enter readily and carry heat to the lower soil.
You have noticed how a pile of stable manure steams in cold weather. You doubtless know that manure from the horse stable is often used to furnish heat for hotbeds and for sweet potato beds.
Now the heat which warms the manure and sends the steam out of it, and warms the hotbed and sweet potato bed, is produced by the decaying or rotting of the manure. More or less heat is produced by the decay of all kinds of organic matter. So if the soil is well supplied with organic matter, the decay of this material will add somewhat to the warmth of the soil.
HOW SOILS LOSE HEAT
Wet one of your fingers and hold your hand up in the air. The wet finger will feel colder than the others and will gradually become dry. This is because some of the heat of your finger is being used to dry up the water or change it into a vapor, or in other words to evaporate it.
In the same manner a wet soil loses heat by the evaporation of water from its surface.
Experiment.—Heat an iron rod, take it from the fire and hold it near your face or hand. You will feel the heat without touching the rod. The heat is radiated from the rod through the air to your body and the rod gradually cools. In the same way the soil may lose its heat by radiating it into the air. A clay soil will lose more heat by radiation than a sandy soil because the clay is more compact.
CONDITIONS WHICH INFLUENCE SOIL TEMPERATURE
It will be noticed that the dry soils are warmer than the wet ones. Why is this? Scientists tell us that it takes a great deal more heat to warm water than it does to warm other substances. Therefore when soil is wet it takes much more heat to warm it than if it were dry.
It will be seen that of the dry soils the humus is the warmest. Why?
Experiment.—Take two thermometers, wrap the bulb of one with a piece of black or dark colored cloth and the bulb of the other with a piece of white cloth, then place them where the sun will shine on the cloth covered bulbs. The mercury in both thermometers will be seen to rise, but in the thermometer with the dark cloth about the bulb it will rise faster and higher than in the other. This shows that the dark cloth absorbs heat faster than the white cloth. In the same manner a dark soil will absorb heat faster than a light colored soil; therefore it will be warmer if dry.
Why was the dry clay warmer than the dry sand?
Because its darker color helped it to absorb heat more rapidly than the sand, and, as the particles were smaller and more compact, heat was carried into it more rapidly by conduction.
Why were the wet humus and clay cooler than the wet sand?
As they were darker in color and the clay was more compact than the sand, they must have absorbed more heat, but they also held more water, and, therefore, lost more heat by evaporation.
Of the dry soils, then, the humus averaged warmest, because, on account of its dark color, it absorbed heat more readily than the others. The dry clay was warmer than the sand on account of its color and compact texture. Of the wet soils the sand was the warmest, because, on account of its holding less moisture, less heat was required to raise its temperature and there was less cooling by evaporation, while the other soils, although they absorbed more heat than the sand, lost more on account of greater evaporation, due to their holding more moisture. Why are sandy soils called warm soils and clay soils said to be cold?
How may we check losses of heat from the soil?
If we make a mulch on the surface of the soil evaporation will be checked and therefore loss of heat by evaporation will be checked also. The mulch will also check the conduction of heat from the lower soil to the surface and therefore check loss of heat by radiation from the surface.
VALUE OF ORGANIC MATTER
Figure 33 illustrates a simple way to show the value of organic matter in the soil. The boxes are about twelve inches square and ten inches deep. They were filled with a clay subsoil taken from the second foot below the surface of the field. To the second box was added sufficient commercial fertilizer to supply the plants with all necessary plant food. To the third box was added some peat or decayed leaves, in amount about ten per cent. of the clay subsoil. The corn was then planted and the boxes were all given the same care. The better growth of the corn in the third box was due to the fact that the organic matter not only furnished food for the corn but during its decay prepared mineral plant food that was locked up in the clay, and also brought about better conditions of air and moisture by improving the texture of the soil. The plants in the second box had sufficient plant food, but did not make better growth because poor texture prevented proper conditions of air and moisture. "And that's another witness" for organic matter. Decaying organic matter or humus is really the life of the soil and it is greatly needed in most of the farm soils of the eastern part of the country. It closes the pores of sandy soils and opens the clay, thus helping the sand to soak up and hold more moisture and lessening excessive ventilation, and at the same time helping the roots to take a firmer hold. It helps the clay to absorb rain, helps it to pump water faster, helps it to hold water longer in dry weather, increases ventilation, favors root penetration and increases heat absorption. We can increase the amount of organic matter in the soil by plowing in stable manure, leaves and other organic refuse of the farm, or we can plow under crops of clover, grass, grain or other crops grown for that purpose.
CHAPTER VIII
PLANT FOOD IN THE SOIL
We learned in previous paragraphs that the roots of plants take food from the soil, and that a condition necessary for the root to do its work for the plant was the presence of available plant food in sufficient quantities.
What is plant food? For answer let us go to the plant and ask it what it is made of.
Experiment.—Take some newly ripened cotton or cotton wadding, a tree branch, a cornstalk, and some straw or grass. Pull the cotton apart, then twist some of it and pull apart; in turn break the branch, the cornstalk and the straw. The cotton does not pull apart readily nor do the others break easily; this is because they all contain long, tough fibres. These fibres are called woody fibre or cellulose. The cotton fibre is nearly pure cellulose. |
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