Now what are the uses of these parts of the flower?
If we watch a flower of the peach or cherry from week to week, we will see that the pistil develops into a peach or cherry which bears within a seed from which a new plant will be produced if the seed is placed under conditions necessary for germination or sprouting.
FIG. 70.—FLOWER OF CHERRY.
a, pistil; b, stamen; c, corolla; d, calyx; e, section of
flower showing ovary with ovule.
(Drawing by M.E. Feltham.)ToList
FIG. 71.
1. Flower of apple; b, stamens; c, corolla; d, calyx. 2. Section
of same; a, style; e, compound ovary; f, filament; g, anther.
(Drawing by M.E. Feltham.)ToList
FIG. 72.
A. Pistil of flowering raspberry; e, ovary; t, style; s,
stigma. B. Stamen of flowering raspberry; f, filament; g,
anther; p, pollen.ToList
FIG. 73.—FLOWER OF BUTTERCUP.
c, petals; d, sepals; h, ripened pistils, or fruit.
(Drawing by M.E. Feltham.)ToList
The pistils of the flowers of other plants will be found to develop into fleshy fruits, hard nuts, dry pods or husks containing one or more seeds.
The work of the pistil or pistils of flowers then is to furnish seeds for the production of new plants.
The botanists tell us that a pistil will not produce seeds unless it is fertilized by pollen from the same kind of flower falling on its stigma.
The work of the stamen then is to produce pollen to fertilize the pistils. Pistils and stamens are both necessary for the production of fruit and seed. They are therefore called the essential or necessary parts of the flower.
The botanists also tell us that nature has provided that in most cases the pistils shall be fertilized by the pollen of some other flower than their own, as this produces stronger seeds.
How is the pollen carried from flower to flower?
Go into the garden or field and watch the bees and butterflies flying about the flowers, resting on them and crawling into them. They are seeking for nectar which the flower secretes. As they visit plant after plant, feeding from many flowers, their bodies become more or less covered with pollen as they brush over the stamens. Some of this pollen in turn gets rubbed off on the stigmas of the pistils and they become fertilized. Thus the bees and some other insects have become necessary as pollen carriers for some of the flowers and the flowers in turn feed them with sweet nectar.
This gives us a hint as to one use of the corollas which spreads out such broad, brightly-colored, conspicuous petals. It must be that they are advertisements or sign boards to attract the bees and to tell them where they can find nectar and so lead them unconsciously to carry pollen from flower to flower to fertilize the pistils. The act of carrying pollen to the pistil is called pollination, and carrying pollen from the stamens of one flower to the pistil of another flower is called cross pollination.
If we examine a blossom bud just before it opens we will see only the calyx. Everything else will be wrapped up inside of it. Evidently, then, the calyx is a protecting covering for the other parts of the flower until blossoming time.
The corolla will be found carefully folded within the calyx and also helps protect the stamens and pistil.
Some flowers do not produce bright-colored corollas to attract the bees, for examples, the flowers of the grasses, wheat, corn, and other grains, the willows, butternuts, elms, pines and others. But they produce large amounts of pollen which is carried by the wind to the pistils.
You have sometimes noticed in the spring that after a rain the pools of water are surrounded by a ring of yellow powder and you have perhaps thought it was sulphur. It was not sulphur but was composed of millions of pollen grains from flowers. One spring Sunday I laid my hat on the seat in church. When I picked it up at the end of the service I found considerable dust on it. I brushed the dust off, but on reaching home I found some remaining and noticed that is was yellow, so I examined it with a magnifying glass and found that it was nearly all pollen grains. Then I rubbed my finger across a shelf in my room and found it slightly dusty; the magnifying glass showed me that this dust was half pollen. This shows what a great amount of pollen is produced and discharged into the air, and it shows that very few pistils could escape even if they were under cover of a building.
To make sure of cross pollination nature has in some cases placed the stamens and pistils in different flowers on the same plant. This will be found true of the flowers of the squashes, melons and cucumber. Below some of the flower buds will be seen a little squash, melon or cucumber (Fig. 75). These are the ovaries of pistils and the stigmas will be found within the bud or will be seen when the bud opens. But no stamen will be found here. Other flowers on these plants will be found to possess only stamens. These staminate flowers produce pollen and then die. They do not produce any fruit, but their pollen is necessary for the little cucumbers, squashes and melons to develop.
Another example is the corn plant. Here the pistils are on the ear, the corn silk being the styles and stigmas, while the pollen is produced in the tassel at the top of the plant.
With some plants we find that not only are the pistils and stamens in separate flowers but the staminate and pistilate flowers are placed on different plants. This will be found true of the osage orange and the willow.
In many flowers that have both stamens and pistils or are perfect flowers the stigmas and pollen ripen at different times.
With some varieties of fruit it is found that the pistils cannot be fertilized by pollen of the same variety. This is true of most of our native plums. For example, the pistils of the wild goose plum cannot be fertilized by pollen of wild goose plums even if it comes from other trees than the one bearing the pistils. They must have pollen from another variety of plum.
Many times it happens that a farmer or a gardener wants to start a strawberry bed and buys plants of a variety of berries that have the reputation of being very productive. He plants them and cultivates them carefully, and at the proper time they blossom very freely, and there is promise of a large crop, yet very few berries appear and this continues to be the case. Not satisfied with them he buys another variety and plants near them, and after that the old bed becomes very productive. Now why is this? It happens that the flowers of some varieties of strawberries have a great many pistils but no stamens, or very few stamens, and there is not pollen enough to fertilize all of the blossoms, and when such a variety is planted it is necessary to plant near it some variety that produces many stamens and therefore pollen enough to fertilize both varieties in order to be sure of a crop. Those strawberries which produce flowers with only pistils are called pistilate varieties, while those with both stamens and pistils are called perfect varieties (Fig. 78). In planting them there should be at least one row of a perfect variety to every four or five pistilate rows.
FIG. 74.
A magnolia flower showing central column of pistils and stamens, the
pistils being above and the stamens below them.ToList
FIG. 75.—FLOWERS OF SQUASH.
A, pistillate flower; B, staminate flower. A means of insuring
cross-pollination.ToList
We have learned that certain varieties of plums cannot be fertilized by pollen from the same variety, and to make them fruitful some other variety must be planted among them to produce pollen that will make them fruitful. This is more or less true of all our fruits. Therefore it is not best generally to plant one variety of fruit by itself. Not knowing this some orchardists have planted large blocks of a single variety of fruit which has been unfruitful till some other varieties have been planted near them or among them.
A knowledge of the necessity of pollination is very important to those gardeners who grow cucumbers, tomatoes, melons and other fruiting plants in greenhouses. Here in most cases the pollination is done by hand.
We noticed that nature provides that most of the flowers shall be cross pollinated. This is particularly true of the flowers of the fruit trees, and for this reason it is impossible to get true varieties of fruit from seed. For example, if we plant seeds of the wine sap apple, the new trees produced from them will not produce the same kind of apple but each tree will produce something different and they will very likely all be poorer than the parent fruit. This is because of the mixture of pollens which fertilize the pistils. Knowing this fact the nurseryman plants apple seeds and grows apple seedlings. When these get to be the size of a lead pencil he grafts them, that is, he digs them up, cuts off the tops away down to the root and then takes twigs from the variety he wishes to grow and sets or splices these twigs in the roots of the seedlings and then plants them. The root and the new top unite and produce a tree that bears the same kind of fruit as that produced by the tree from which the twig was taken.
These are a few of the reasons why it is well to know something about flowers and their work.
FIG. 76.—FLOWER OF A LILY.
Notice how the stigma and the anthers are kept as far as possible from
each other to guard against self-pollination and to insure
cross-pollination.ToList
FIG. 77.
Bud and flower of jewel-weed, or "touch-me-not." A. Interior of bud.
Stamens are seen, but there appears to be no pistil. B. Section of
bud showing the pistil concealed behind the stamens. C. Bee entering
flower comes in contact with stamens and is loaded with pollen. D.
Same bee entering older flower. The stamens have ripened and been
pushed off by the lengthened pistil, which is brushed by the back of
the bee, and thus is pollinated. This is a contrivance to insure
cross-pollination.ToList
FIG. 78.
A. Pistillate flower of strawberry. B. Perfect flower of strawberry.
(Drawing by M.E. Feltham.)ToList
The pistil develops and forms the fruit of the plant. This fruit bears seed for the production of new plants. This fruit may be a dry pod like the bean or pea, or it may be a fleshy fruit like the apple or plum. Now the developing pistil or fruit may be checked in its work of seed production by insects and diseases, and to secure good fruit it is in many cases necessary to spray the fruits just as the leaves are sprayed, to keep these insects and diseases in check.
The fruits of most plants, like the leaves, need light and air for their best development, and it sometimes happens that the branches of the fruit trees grow so thick that the fruits do not get sufficient light and air. This makes it necessary to thin the branches or in other words to prune the tree. Some trees also start more fruit than they can properly feed and as a result the ripened fruits are small and the tree is weakened. This makes it necessary to thin the fruits while they are young and undeveloped.
What is a fertile soil?
The expression a fertile soil is often used as meaning a soil that is rich in plant food. In its broader and truer meaning a fertile soil is one in which are found all the conditions necessary to the growth and development of plant roots.
These conditions, as learned in Chapter II, are as follows:
The root must have a firm yet mellow soil.
It must be well supplied with moisture.
It must be well supplied with air.
It must have a certain amount of heat.
It must be supplied with available plant food.
In order to furnish these needs or conditions the soil must possess certain characteristics or properties.
These properties may be grouped under three heads:
Physical properties; the moisture, heat and air conditions needed by the roots.
Biological properties; the work of very minute living organisms in the soil.
Chemical properties; plant food in the soil.
Three very important physical properties of a fertile soil are its
Power to take water falling on the surface.
Power to absorb water from below.
Power to hold water.
The fertile soil must possess all three of these powers. The relative degrees to which these three powers or properties are possessed determine more than anything else the kind of crops or the class of crops that will grow best on a given soil.
These powers depend, as we learned in Chapter IV, on the texture of the soil or the relative amounts of sand, silt, clay and humus contained in the soil.
The power of admitting a free circulation of air through its pores is also an important property of a fertile soil, for air is necessary to the life and growth of the roots. This property is dependent also on texture.
Two other important properties of a fertile soil are power to absorb and power to hold heat. These depend upon the power of the soil to take in warm rain and warm air, and also upon density and color. The denser or more compact soil and the darker soil having greater power to absorb heat.
The compactness of the soil which gives it greater powers to absorb heat weakens its powers to hold it, because the compactness allows more rapid conduction of heat to the surface, where it is lost by radiation.
The more moisture a soil holds, the weaker is its heat-holding power, because the heat is used in warming and evaporating water from the surface of the soil.
These important properties or conditions of moisture, heat and air, are, as we have seen, dependent on soil texture and color, which in turn are dependent upon the relative amounts of sand, clay and humus in the soil. We are able to control soil texture and therefore these physical properties to a certain degree by means of tillage and the addition of organic matter or humus (see Chapter IV).
Biology is the story or science of life; and the biological properties of the soil have to do with living organisms in the soil.
The soil of every fertile field is full of very small or microscopic plants called bacteria or germs. They are said to be microscopic because they are so small that they cannot be seen without the aid of a powerful magnifying glass or microscope. They are so small that it would take about 10,000 average-sized soil bacteria or soil germs placed side by side to measure one inch.
A knowledge of three classes of these soil germs is of great importance to the farmer. These three classes of germs are:
Nitrogen-fixing germs.
Nitrifying germs.
Denitrifying germs.
We learned in Chapter VIII that nitrogen is one of the necessary elements of plant food, and that although the air is four-fifths nitrogen, most plants must take their nitrogen from the soil. There is, however, a class of plants called legumes which can use the nitrogen of the air. Clover, alfalfa, lucern, cowpea, soy bean, snap bean, vetch and similar plants are legumes. These legumes get the nitrogen from the air in a very curious and interesting manner. It is done through the aid of bacteria or germs.
Carefully dig up the roots of several legumes and wash the soil from them. On the roots will be found many small enlargements like root galls; these are called nodules or tubercles. On clover roots these nodules are about the size of the head of a pin while on the soy bean and cowpea they are nearly as large as a pea (see Fig. 34). These nodules are filled with bacteria or germs and these germs have the power of taking nitrogen from the air which finds its way into the soil. After using the nitrogen the germ gives it to the plant which then uses it to build stem, leaves and roots. In this way the legumes are able to make use of the nitrogen of the soil air, and these germs which help them to do it by catching the nitrogen are called nitrogen-fixing germs.
The work of these germs makes it possible for the farmer to grow nitrogen, so to speak, on the farm.
By growing crops of legumes and turning them under to decay in the soil, or leaving the roots and stubble to decay after the crop is harvested, he can furnish the following crop with a supply of nitrogen in a very cheap manner and lessen the necessity of buying fertilizer.
Almost all the nitrogen of the soil is locked up in the humus and cannot in that condition be used by the roots of plants. The nitrogen caught by the nitrogen-fixing germs and built into the structure of leguminous plants which are grown and turned under to feed other plants cannot be used until the humus, which is produced by their partial decay, is broken down and the nitrogen built into other substances upon which the root can feed. The breaking down of the humus and building of the nitrogen into other substances is the work of another set of bacteria or germs called nitrifying germs.
These nitrifying germs attack the humus, break it down, separate the nitrogen, cause it to unite with the oxygen of the air and thus build it into nitric acid which can be used by plant roots. This nitric acid if not immediately used will unite with lime or potash or soda or other similar substances and form nitrates, as nitrate of lime, nitrate of potash or common saltpetre. These nitrates are soluble in water and can be easily used by plant roots. If there are no plant roots to use them they are easily lost by being washed out of the soil. The work of the nitrifying germs is called nitrification.
To do their work well the nitrogen-fixing germs and the nitrifying germs require certain conditions.
The soil must be moist.
The soil must be well ventilated to supply nitrogen for the nitrogen-fixing germs and oxygen for the nitrifying germs.
The soil must be warm. Summer temperature is the most favorable. Their work begins and continues slowly at a temperature of about forty-five degrees and increases in rapidity as the temperature rises until it reaches ninety or ninety-five.
The nitrifying germs require phosphoric acid, potash and lime in the soil.
Direct sunlight destroys these bacteria, therefore they cannot work at the surface of the soil unless it is shaded by a crop.
From this we see that these bacteria or germs work best in the soil that has conditions necessary for the growth and development of plant roots.
These germs live on the coarse organic matter of the soil. Like the nitrifying germs they need oxygen, and when they cannot get it more readily elsewhere they take it from the nitric acid and nitrates. This allows the nitrogen of the nitrates to escape as a free gas into the air again, and the work of the nitrogen-fixing and nitrifying germs is undone and the nitrogen is lost. This loss of nitrogen is most apt to occur when the soil is poorly ventilated, because of its being very compact, or when the soil spaces are filled with water. This loss of nitrogen by denitrification can be checked by keeping the soil well ventilated.
By the term chemical properties we have reference to the chemical composition of the soil, the chemical changes which take place in the soil, and the conditions which influence these changes.
The sand, clay and humus of the soil are made up of a great variety of substances. The larger part of these act simply as a mechanical support for the plants and also serve to bring about certain physical conditions. Only a very small portion of these substances serve as the direct food of plants and the chemical conditions of these substances are of great importance.
In Chapter VIII we learned that plants are composed of several elements and that seven necessary elements are taken from the soil. These seven are nitrogen, phosphorus, potassium, magnesium, calcium, iron and sulphur.
Now a fertile soil must contain these seven elements of plant food and they must be in such form that the plant roots can use them.
Plant roots can generally get from most soils enough of the magnesium, calcium, iron, and sulphur to produce well developed plants. But the nitrogen, phosphorus and potassium, although they exist in sufficient quantities in the soil, are often in such a form or condition that the roots cannot get enough of one or more of them to produce profitable crops. For this reason these three elements are of particular importance to the farmer for, in order to keep his soil fertile, he must so treat it that these elements will be made available or he must add more of them to the soil in the proper form or condition.
Nitrogen in the soil.—Plant roots use nitrogen in the form of nitric acid and salts of nitrogen called nitrates. But the nitrogen of the soil is very largely found in the humus with the roots cannot use. A chemical change must take place in it and the nitrogen be built into nitric acid and nitrates. This, we have learned, is done through the aid of the nitrifying germs.
Phosphoric acid in the soil.—Phosphorus does not exist pure in the soil. The plant finds it as a phosphoric acid united with the other substances forming phosphates. These are often not available to plants, but can to a certain extent be made available through tillage and by adding humus to the soil.
Potash in the soil.—The plant finds potassium in potash which exists in the soil. Potash like phosphoric acid often exists in forms which the plant cannot use but may be made available to a certain extent by tillage, the addition of humus, and the addition of lime to the soil.
Lime in the soil.—Most soils contain the element calcium or lime, the compound in which it is found, in sufficient quantities for plant food. But lime is also of importance to the farmer and plant grower because it is helpful in causing chemical changes in the soil which tend to prepare the nitrogen, phosphoric acid and potash for plant use. It is also helpful in changing soil texture.
The chemical changes which make the plant foods available are dependent on moisture, heat, and air with its oxygen, and are therefore dependent largely on texture, and therefore on tillage.
When good tillage and the addition of organic matter and lime do not render available sufficient plant food, then the supply of available food may be increased by the application of manure and fertilizers.
It will be seen that all these classes of properties are necessary to furnish all the conditions for root growth.
The proper chemical conditions require the presence of both physical and biological properties and the biological work in the soil requires both chemical and physical conditions.
From the farmer's standpoint the physical properties seem to be most important, for the others are dependent on the proper texture, moisture, heat and ventilation which are controlled largely by tillage.
Therefore the first effort of the farmer to improve the fertility of his soil should be to improve his methods of working the soil.
Every one of these properties of the fertile soil, and consequently every one of the conditions necessary for the growth and development of plant roots, is influenced in some way by every operation performed on the soil, whether it be plowing, harrowing, cultivating, applying manure, growing crops, harvesting, or anything else, and the thoughtful farmer will frequently ask himself the question: "How is this going to effect the fertility of my soil or the conditions necessary for profitable crop production?"
The important factors in maintaining or increasing the fertility of the soil are:
The mechanical operations of tillage, especially with reference to the control of soil water.
The application of manures and fertilizers, especially with reference to maintaining a supply of humus and plant food.
Methods or systems of cropping the soil, with reference to economizing fertility.
The more important tillage tools and tillage operations we studied in Chapters XI and XII. They will be noticed here only in connection with their influence over soil water, for in the regulation of this important factor in soil fertility the other conditions of fertility are also very largely controlled.
"Of all the factors influencing the growth of plants, water is beyond doubt the most important," and the maintaining of the proper amount of soil water is one of the most important problems of the thinking farmer in controlling the fertility of his soil.
The decay of mineral and organic matter in the soil, and the consequent setting free of plant food, can take place only in the presence of moisture. The plant food in barn manures and crops plowed under for green moisture, can be made available only when there is sufficient moisture in the soil to permit breaking down and decomposition.
The presence of moisture in the soil is necessary for the process of nitrification to take place.
Soil moisture is necessary to dissolve plant food. Plant roots can absorb food from the soil only when it is in solution, and it seems to be necessary that a large quantity of water pass through the plant tissues to furnish the supply of mineral elements required by growth.
Moisture is necessary to build plant tissues. The quantity of water entering into the structure of growing plants varies from sixty to as high as ninety-five per cent, of their total weight.
During the periods of active growth there is a constant giving off of moisture by the foliage of plants and this must be made good by water taken from the soil by their roots.
In a series of experiments at the University of Wisconsin Agricultural Experiment Station, it was found that in raising oats, every ton of dry matter grown required 522.4 tons of water to produce it; for every ton of dry matter of corn there were required 309.8 tons of water; a ton of dry red clover requires 452.8 tons of water to grow it. At the Cornell University Agricultural Experiment Station, a yield of potatoes at the rate of 450 bushels per acre represented a water requirement of 1310.75 tons of water.
The soil which is occupied by the roots of plants receives moisture in the form of rain, snow and dew from above and free and capillary water rising from below.
"Free water is that form of water which fills our wells, is found in the bottom 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." Free water is not used directly by plants unless they are swamp plants, and its presence within eighteen inches of the surface is injurious to most farm plants. Free water serves as the main source of supply for capillary water.
"Capillary water is water which is drawn by capillary force or soaks into the spaces between the soil particles and covers these particles with a thin film of moisture." It is a direct source of water to plants. Capillary water will flow in any direction in the soil, the direction of flow being determined by texture and dryness, the flow being stronger toward the more compact and drier parts. If the soil is left lumpy and cloddy then capillary water cannot rise readily from below to take the place of that which is lost by evaporation. If, however, the soil is fine and well pulverized, the water rises freely and continuously to supply the place of that taken by plant roots or evaporation from the surface.
Some farm lands contain too much water for the growth of farm crops; for example, bottom lands which are so low that water falling on the surface cannot run off or soak down into the lower soil. The result is that the spaces between the soil particles are most of the time filled with water, and this checks ventilation, which is a necessary factor in soil fertility. This state of affairs occurs also on sloping uplands which are kept wet by spring water or by seepage water from higher lands. Some soils are so close and compact that water falling on the surface finds great difficulty in percolating through them, and therefore renders them too wet for profitable cropping during longer or shorter periods of the year. Nearly all such lands can be improved by removing the surplus water through drains. (See Chapter XXV.)
Percolation and ventilation of close compact soils can be improved by mixing lime and organic matter with them.
In some sections of the country, particularly the arid and semi-arid sections of the West, the soil does not receive a sufficient supply of rain water for the production of profitable yearly crops. These soils are rendered unfertile by the lack of this one all important factor of fertility. They can be made fertile and productive by supplying them with sufficient water through irrigation.
The crop-producing power of some lands is lowered even in regions where the rainfall is sufficient, because these lands are not properly prepared by tillage and the addition of organic matter to absorb and hold the water that comes to them, or part of the water may be lost or wasted by lack of proper after-tillage or after-cultivation. This state of affairs is of course improved by better preparation to receive water before planting the crop and better methods of after-cultivation to save the water for the use of the crop.
Aside from what is used by the crops the soil may lose its water in the following ways:
Rain water which comes to the soil may be lost by running off over the surface of the land. This occurs especially on hilly farms and in the case of close, compact soils.
Water may be lost from the soil by leaching through the lower soil.
Water may be lost from the soil by evaporation from the surface.
The soil may lose water by the growth of weeds which are continually pumping water up by their roots and transpiring it from their leaves into the air.
Plowing and soil water. One of the first effects of deeply and thoroughly plowing a close, compact soil, is that rain will sink into it readily and not be lost by surface wash. In many parts of the country, especially the South, great damage is done by the surface washing and gulleying of sloping fields.
The shallow layer of soil stirred up by small plows and practice of shallow plowing so prevalent in the South takes in the rain readily, but as the harder soil beneath does not easily absorb the water the shallow layer of plowed soil soon fills, then becomes mud, and the whole mass goes down the slope. Where the land is plowed deep there is prepared a deep reservoir of loose soil that is able to hold a large amount of water till the harder lower soil can gradually absorb it.
The soil stirred and thoroughly broken by the plow serves not only as a reservoir for the rainfall, but also acts as a mulch over the more compact soil below it, thus checking the rapid use of capillary water to the surface and its consequent loss by evaporation. The plow which breaks and pulverizes the soil most thoroughly is the one best adapted to fit the soil for receiving and holding moisture.
If the plowing is not well done or if the land is too dry when plowed and the soil is left in great coarse lumps and clods, the air circulates readily among the clods and takes from them what little moisture they may have had and generally the soil is left in a worse condition than if it had not been plowed at all.
Fall plowing on rolling land and heavy soil leaving the surface rough helps to hold winter snows and rains when they fall, giving to such fields a more even distribution of soil water in the spring.
Spring plowing should be done early, before there is much loss of water from the surface by evaporation.
Professor King, of the University of Wisconsin Agricultural Experiment Station, carried on an experiment to see how much soil water could be saved by early plowing. He selected two similar pieces of ground near each other and tested them for water April 29th. Immediately after testing one piece was plowed. Seven days later, May 6th, he tested them for water again and found that both had lost some water, but that the piece which was not plowed had lost 9.13 pounds more water per square foot of surface than the plowed piece. This means that by plowing one part a week earlier than the other he saved in it water equal to a rainfall of nearly two inches or at the rate of nearly 200 tons of water per acre.
These operations when properly and thoroughly done tend to supplement the work of the plow in fitting the soil to absorb rain and in making a mulch to check loss by surface evaporation. The entire surface should be worked and the soil should be left smooth and not in ridges. Rolling cutters and spring-toothed harrows are apt to leave ridges and should have an attachment for smoothing the surface or be followed by a smoothing harrow. Cultivators used to make mulches to save water should have many narrow teeth rather than few broad ones. If a large broad-toothed tool is used to destroy grass and large weeds it should be followed by a smoother to level the ridges and thus lessen the evaporating surface. The soil should be cultivated as soon after a rain as it can be safely worked.
Rolling compacts the soil and starts a quicker capillary movement of water toward the surface and a consequent loss by evaporation. When circumstances will permit, the roller should be followed by a light harrow to restore the mulch.
Ridging the land tends to lessen the amount of moisture in the soil because it increases the evaporating surface. It should be practiced only on wet land or in early spring to secure greater heat.
Drains placed in wet land remove free water to a lower depth and increase the depth of soil occupied by capillary water and therefore increase the body of soil available to plant roots.
Humus, as we learned in Chapter IV, has a very great and therefore important influence over the water-absorbing and water-holding powers of soils. Therefore, any of the farm practices that tend to increase or diminish the amount of humus in the soil are to be seriously considered because of the effect on the water content of the soil. For this reason the application of barn manures and green crops turned under tend to improve the water conditions of most soils.
The mixing of heavy applications of coarse manures or organic matter with light sandy soils may make them so loose and open that they will lose moisture rapidly. When this practice is necessary the land should be rolled after the application of the manure.
Constant tillage hastens the decay of organic matter in the soil. Hence any method or system of cropping which does not occasionally return to the soil a new supply of humus tends to weaken the powers of the soil toward water.
All of the operations and practices which influence soil water also affect the other conditions necessary to root growth; namely, texture, ventilation, heat, and plant food, and those operations and practices which properly control and regulate soil water to a large degree control and regulate soil fertility.