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SOILS |
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KEY CONCEPTS
II. Soil Horizons
III. Soil Formation
V. Soil Modifications
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SOIL MODIFICATIONS
Mechanical modification is merely a means of improving soil structure by digging, in one form or another. A shovel, spade, garden fork or rototiller mechanically modifies soil. Dig or till when soil is neither too wet nor too dry.
COMPACTION reduces pore space in soil. It can result from improper digging or tilling. When preparing to install a lawn or garden, avoid use of heavy machinery. Rototill only when necessary. Observation shows that earth worms leave rototilled soil. Rototilling also lessens BIOLOGICAL DIVERSITY in the soil. Both factors have a negative impact upon the overall quality of garden soil. Digging in or walking on wet soils causes compaction. Once organic matter has been tilled into the soil, keep off the soil. Use paths or lay down boards that distribute weight more evenly over an area. A good rule is to work the soil no more than necessary to achieve desired soil structure. Some gardeners DOUBLE DIG to increase soil pore space. This is a very labor-intensive method of cultivation. When double digging, it is wise to add amendments recommended in a soil test.
Another way to improve the quality of soil is by the addition of various amendments, such as fertilizer, peat moss, compost, manures, worms, INOCULANTS, SHARP SAND, lime, "green manures" or COVER CROPS, mulches and SEWAGE
SLUDGE*. Humus, peat moss, sludge, manures and cover crops will increase water-holding capacity of sandy soil by increasing surface area to which moisture can cling. They also can be used to break up clay by forming aggregates.
*CAUTION: Sewage sludge may contain heavy metals such as copper, zinc, nickel, lead and cadmium. Carefully read the label. These products should not be used in vegetable gardens. Some "organic fertilizer" products are sewage sludge.
Fertilizers, sludge, manures and green manures add some nutrients. Lime and sulphur are used to adjust pH. In small areas, sharp sand can be added to clay soil along with organic matter to alter the soil's texture. Gypsum is sold as a soil conditioner for poorly-drained clay soil; however, it does not improve soil structure or drainage. Gypsum is a source of calcium and sulfur, but these elements are in good supply in Ohio soils. The only reason to use gypsum in Ohio is in soil that is contaminated with salt.
A gardener's most valuable soil amendment is humus, often referred to as "gardener's gold" or "back gold." Composting is the production of humus from selected garden and kitchen wastes. Microbes break down organic raw materials into humus, as they do leaves on the forest floor. Composting is a great way to get rid of yard waste and improve soil structure with no negative impact on the environment.
HUMUS is organic matter in a form plants can use. It adds small amounts of nutrients. Humus improves soil structure, water-holding capacity and nutrient-holding capacity. It costs almost nothing to produce and diverts yard waste from landfills.
Humus has an advantage over the use of unprocessed organic matter such as fresh grass clippings, garden debris, leaves, sawdust and wood chips. Microbes use nitrogen in the process of breaking down this organic matter. Nitrogen is the single most important nutrient in plant growth. Because decomposition depletes nitrogen, nitrogen should be added where large amounts of unprocessed organic matter are used.
These are the benefits of adding humus to garden soil:
- There is scientific evidence that fruits and vegetables grown in humus have a higher sugar content. This gives them a "sweeter" taste.
- The darker color of humus increases the absorption of sunlight. Highly organic soil warms up faster in spring.
- Humus improves the "crumb structure" of soil, preventing a hard crust from forming on the surface. Germinating seedlings can easily push through and roots can easily grow.
- Humus attracts earthworms that burrow up from nutrient-rich subsoil, depositing nutrients in the topsoil layer.
A pile is the ideal form of making compost in the small home garden. Local ordinances should be checked before starting a compost pile. For this method, a minimum of one cubic yard of space (3'x 3'x 3') is needed. The ideal ratio of dry (brown) organic matter to wet (green) organic matter should be 30 to 1. This means 30 bushels of dry leaves or straw to 1 bushel of grass clippings. An easier method to approximate this ratio is to add equal weights of dry and wet materials.
Additions to the compost pile can include the following:
Dry Organic Material:
newspaper/paper (no glossy paper)
hay or straw
branches, evergreen needles
sawdust
dried leaves
Wet Organic Material:
any green plant materials
nongreasy kitchen scraps (eggshells, vegetable and fruit
scraps)
manure (no cat, dog or human feces)
A compost pile produces humus over a period that varies from a few weeks to a year or longer. Composting methods that produce high temperatures (140 degrees F) will kill weed seeds and disease organisms and break down most pesticides on plant material. Plant material treated with insecticides, miticides or herbicides should be composted for a minimum of 6 months.
[diagram of compost pile]
Layers of organic matter should be 2 to 4" thick. Smaller pieces of matter decompose more quickly. A shredder-chipper or lawn mower can assist in this process. Air space and water are both essential for decay. Layers should be loose and moist. The moisture level should be that of a wrung-out sponge. Adding a few shovelsful of garden soil and turning the compost promotes faster decomposition. The addition of fertilizer containing nitrogen speeds decay if you lack enough green material. It adds to the nutrient value of the finished product. Lime is often added to the compost pile, but is not necessary.
Composting is not an exact process. Realistically, gardeners will compost the plant materials they have available to them. It may not consist of the ideal combination of wet and dry material. This may add to the time needed for decomposition. A properly constructed compost pile is practically odorless. The only time an odor problem will arise is when thick layers of fresh grass clippings are added.
Trench composting is a method of COLD COMPOSTING used for gardens or small farms. Dig a long trench 6-8 inches deep between crop rows. Place disease-free, organic litter not treated with pesticides in the bottom of the trench. Cover with a few inches of soil. Do not add more than a few inches of soil because more biological activity occurs closer to the soil surface. Decomposition takes one season. Even very fibrous garden waste, such as tough stalks, decompose in one year with this method. Peas and beans can be planted directly in the trench. These two vegetables are able to "fix" nitrogen in their roots. The action of decomposition will not disturb their nitrogen requirements.
GREEN MANURES or cover crops are another means of protecting and improving soil quality. For example, winter rye or annual ryegrass is planted in fall to be turned into the soil in spring. Sowing time varies with the cover crop to be grown. Green manure benefits the soil in several ways:
- provides organic matter
- holds nutrients that may be lost over winter
- reduces erosion and loss of topsoil
- LEGUME cover crops can increase amount of nitrogen in soil
- a deep-rooted cover crop allowed to grow for a season in hard soil (HARDPAN) greatly improves the soil's tilth
Notice that green manures do not necessarily add nutrients (except for legumes). Actually, they remove nutrients as they grow. Their decomposition, after being turned, again takes nitrogen from the soil. However, green manures will hold animal manure nutrients in the soil. Turn these cover crops into the soil at least two weeks before planting. Never allow them to go to seed.
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