Soil, the basic stuff of life, consists of the upper layer of the earth in which plants grow and obtain their food.
It is formed by physical and chemical weathering due to the interaction between wind, water, heat, cold, ice, plant growth, and animals.
For the most part, soil processes are biological in nature. Therefore, adding organic matter and the following decaying process is essential for healthy soil.
What Makes A Soil’s Make-Up
Soil consists of mineral materials, organic matter, water, and air.
The water and air are not in a continuous liquid or gaseous body but dispersed in the pore spaces between the layers of solid soil particles.
Thus the make-up and handling of your garden soil influence the relative amounts of water and air present.
Soil Moisture
When soil moisture is at its optimum (for plants’ successful growth), soil air’s humidity approaches 100% — a condition that hastens chemical reactions and favors the growth of bacteria and other soil organisms.
Soil Texture
Actually, the texture of your soil depends upon the size of the individual particles. These range from coarse sand and gravel (visible to the naked eye) to medium fine silt particles (visible under a microscope) and very fine clay particles, many of which are sub-microscopic.
Sandy soils are coarse textured, while clays are fine textured. Although sandy soils are called light, they are heavy in weight. On the other hand, clay soils are called heavy but are light by weight when they are dry.
The term soil structure refers to how soil particles are grouped with one another. They may be entirely separate as in sand (single grain structure), or they may be held together by colloidal matter to form a group in which they remain united under ordinary conditions.
Soil Consistency
When soil particles thus adhere, the resulting soil consistency is called crumb structure.
Colloidal particles are plentiful in clay and responsible for their shrinkage, plasticity, and tenacity.
In fact, they are very small, some being only 1/21,000 the size of a large sand particle.
Together, however, these surround the soil particles in a thin film, making the surfaces on which all essential soil activities occur.
Note that this is the only area where root hairs function. Fundamentally, the soil’s physical structure is more important than its richness.
Improving Soil Structure
Working the soil by spading or cultivating and adding humus and plant food are necessary steps in improving its structure.
When so treated, the soil becomes loamy. Good silt loam contains 45% mineral particles, 5% organic matter, 25% soil water, and 25% soil air.
Preparing the soil for a garden by spading (or plowing large areas) is done in spring or fall.
Clay soils benefit from fall spading if organic matter is present or can be added. In any event, the soil should not be disturbed when wet.
During the growing season, cultivation breaks up crusts induced by heavy rains, kills weeds, and helps aeration.
However, if weed control is not a consideration, cultivation should be discontinued. Too much of it impairs good filth.
Strange as it may seem, the value of humus is little understood. Humus has been called the key material of the life cycle.
The wheel of life in the soil is made up of growth and decay, both of which are essential links in the conservation of matter and energy.
Role Of Fungi And Bacteria
Then, fungi and bacteria also play an important role in the soil. For example, decay would not occur without the action of bacteria which convert organic waste into humus by oxidation.
However, their action is slower than that of fungi. Thus, adding small amounts of humus yearly is better than a large quantity every few years.
A small increase in humus content has beneficial effects on the soil far greater in proportion than the amount used.
The Nitrogen Cycle
Soil yields crops. The sun working on green leaf tissue produces carbohydrates and proteins in a process called photosynthesis.
Chlorophyll, or green coloring matter, is a necessary enzyme in this process.
By absorbing water through a plant’s roots, carbon dioxide (CO2), and radiant energy from the sun through its leaves, carbohydrates are stored up.
These are made of carbon (C), oxygen (O), and hydrogen (H) — three of the essential elements. There is no alternative source. These become animal protoplasm.
Work of Bacteria
As soon as animals and plants die, bacteria start working on them to reduce their protoplasm to the simple substances of carbon (C) and nitrogen (N) again.
Bacteria change the protein molecules to ammonia. Then nitrite and nitrate bacteria change them into nitrates which plants can assimilate.
Humus furnishes energy below the ground comparable to photosynthesis in the green plant.
Without humus, the volume of pore space is reduced, and aeration of the soil is impeded. As a result, there is insufficient organic matter for the soil population.
Machinery Of The Soil
Then, the machinery of the soil runs down, and the supply of oxygen (0), water (H20), and salts are reduced. Finally, the synthesis of carbohydrates and proteins is reduced, and plant growth is affected.
We should realize that soil is fertile only when the environment for root growth is favorable, with adequate oxygen (O) and low carbon dioxide (CO2), as well as the right pH, water, nutrients, and lime.
Farm Manure
All good gardeners know that farm manure is an important adjunct to gardening when it can be obtained.
The chief value of manure is in the bacteria that it contains. It is primarily a source of organic matter rather than plant nutrients.
Cow Manure
Cow manure is best for light soils, and horse manure is for heavy soils. Fresh manure may be applied to heavy land in the fall.
It is, of course, high in nitrogen (N) besides containing weed seeds and possibly grubs. Well-rotted manure is applied after spading in the spring.
It is safer and more even in its action than fresh manure but has lost much of its plant food value.
Light Application Of Manure
For a light application of manure, spread 1/16 cord over 1000 square feet.
For a medium application, use a 1/8 cord to 1000 square feet, but for a heavy application, increase the amount of manure to one-fourth cord per 1000 square feet.
(One ton equals one-half cord. One cubic yard equals one-fifth of a cord.)
Use 40 pounds of superphosphate per 1000 square feet with the manure. Actually, using stable manure and superphosphate alone is insufficient to maintain soil fertility.
These must be properly coordinated with lime, commercial fertilizers, leguminous cover crops, good tillage, weed removal, and control of soil water and erosion.
Storing Manure In The Open
If manure must be stored in the open, have flat piles not less than 4’ feet deep with sides steep enough to shed water.
Keep this pile moist and compact. The soil beneath the pile should be puddled or covered with cement. Cover the pile with a thin layer of soil to prevent ammonia loss.
Loose piles, stored in summer, lose two-thirds of their organic matter, nitrogen (N) and potassium (K), in addition to two-fifths of their phosphorus (P) content.
Spreading Manure Directly
Since manure is scarce in many areas, this is an unnecessary waste. Therefore, whenever possible, manure should be spread directly on the fields daily.
If the land is sloping, however, much soluble potash and nitrogen will be washed out in spring thaws.
Superphosphate and peat moss or muck added to hen manure makes a strong but well-balanced plant food.
Use one pound of superphosphate to one bushel of fresh hen manure.
New Nitrogen
Leguminous plants are the foundation on which agriculture rests, and man is dependent. These add new nitrogen (N) to the soil, where humus and manure use old nitrogen over again.
If all available land were put into such crops in a 4-year rotation, these crops would produce 20 times the nitrogen made commercially in this country in a year.
Buckwheat, soybeans, and winter rye are crops that increase the amount of organic matter in the soil when sufficient stable manure is unavailable. Such materials are green manure crops.
Compost Heaps
Compost heaps are an extremely important source of organic matter, which is best applied to the soil as a top dressing in the fall, if not completely broken down or in spring if oxidation is complete.
There are several methods of building a compost heap, but the theory is much the same in all of them.
Alternate layers of manure and vegetable material are piled in varying thicknesses according to the kind of refuse incorporated.
Covering The Finished Pile
Layers of soil are introduced on top of the manure layers and as a covering for the finished pile.
No greasy material should be used. The pile should be kept moist (but not wet) to encourage vigorous bacterial action.
Commercial fertilizers, ground limestone, wood ashes, and superphosphate are usually added to the pile in small amounts.
When manure is not available, the use of bacterial activators can be substituted.
44659 by Kathryn S. Taylor