The words "loam" and "topsoil" are often used interchangeably to refer to rich soil used to improve rocky or infertile soil, but there are some important distinctions between the two terms.
Topsoil or Loam?
Topsoil refers to any type of soil that makes up the upper layer of soil. Loam is used to describe the texture of soil. Loam can be topsoil, but not all topsoil is loam.
Topsoil is the result of organic matter decaying and rocks weathering over hundreds of years. Organic matter usually comprises between 2 and 10 percent of topsoil, resulting in it being darker in color than the subsoils.
Loam consists of clay, sand and silt. The best loam is about 25 percent clay, 25 percent silt and 50 percent sand. That composition allows loam to hold enough moisture for plants, while still draining adequately for air circulation.
Loam Is Best Topsoil
Loam is the best topsoil because of its composition. Large particles of sand provide good aeration, while small pieces of clay hold moisture. Silt is smaller than sand, but larger than clay, and has the properties of both. Loam may be called sandy loam, silty loam or clay loam, depending upon the proportions of each component.
Topsoil should be bought from a reliable vendor. A soil test should be done to determine the pH and soil texture. Topsoil should contain organic matter, but should not include any rocks, trash or debris. If putting soil in your garden, also make sure it is relatively free of roots and seeds of noxious weeds, particularly ground ivy and crabgrass. It should have a fresh clean odor—not sour or chemical-like.
Topsoil can be amended to make it more like loam. Heavy clay soils can be mixed with sand and silt, while sandy soils can be amended with clay. These techniques can be labor-intensive and work best for relatively small areas, such as garden beds.
Loam soil is known for being able to easily retain water, as well as for its moist and gritty texture. Some soils naturally have a loamy texture, while others require some amendment in order to have loamy traits.
Loam soil is popular for gardening because of its capacity to retain a lot of moisture while enabling the water to still be able to freely move about. Loam soil also drains well, which allows sufficient amounts of air to travel to the roots of plants. Unlike sandy soil types, loam soil is efficient for nutrient retention, and it's much more fertile.
It is helpful to be able to know how to identify whether a specific soil is loam soil. The particles of clay, silt and sand that are contained within loam soil are evenly blended together. Unlike clay soils, loam soil is neither tenacious nor stiff. It has a high porosity, which permits high air circulation. Loam soil feels crumbly and rich and usually has a dark appearance.
Soil Specific Gravity
As it relates to gardening and garden chemistry, specific gravity describes the compactness of your garden's soil. Some common specific gravities for soil types are:
Sand = 2.63
Silt = 2.7
Clay = 2.9
Since clay has a high specific gravity compared to other soils, it is more compact. Plant roots will have a hard time growing and spreading out. Clay soils are often amended to reduce their specific gravity for this reason.
Organic soil blends are typically much less dense. Their specific gravity is typically below 2.0, depending on the manufacturer. Organic soils are as a result much less dense and easier for gardening use, making them widely used by gardeners.
Alluvial Plains (Delta)
The Arkansas Delta is the eastern part of the state that runs along the Mississippi River. The soil found in this area is a loose, mineral-rich soil that may even contain traces of valuable materials such as gold and others gems. Created by river erosion, this soil is extremely rich and fertile.
Loess (Crowley's Ridge)
Crowley's Ridge is a small rolling hill that rises above the flat, alluvial plains of the Delta. The soil found here, called loess, is an accumulation of wind-blown silt and bits of clay. It is quick to erode when introduced to water or wind, and is also very fertile soil.
Sandy Loam (Coastal Plain)
The West Gulf Coastal Plain in Arkansas is around the southeastern part of the state, near Louisiana. Characterized by farms and lush forests, the soil found here is sandy loam. Loam, composed of sand, silt and clay, is moist and fertile. As it is easier to till than some soils, farmers often choose to farm on this land.
Residual Shale and Sandstone (Ouachitas)
The Ouachita Mountains run from Oklahoma through central Arkansas, with the Ouachita River running through. The soil found here includes shale and sandstone, which are sedimentary soils that contain mostly clay and tiny particles of crystals such as quartz. As opposed to looser soils, shale is typically found in gray, rock-like sheets with layers that easily break off.
Residual Limestone (Ozarks)
The Ozark Mountains run along the northern part of Arkansas. The soil found here is residual limestone, which is a sedimentary rock made up of silt, sand, clay and often traces of marine organisms' skeletal structures, such as coral. Limestone can erode over time.
The best soil for water retention contains plenty of organic matter. Sandy soils allow water to drain too quickly, and clay soils prevent water from draining into the soil.
Stony Loam Soil
Very stony loam soil prevails in many parts of Oregon. Baker County is predominately composed of stony loam. Clay and silty lake bed sediments, carried by glaciers, makes up the soil content. In many areas, these sediments have washed over and covered the tailings of gold dredging activities from the late 1800s.
Oregon Soil Distribution
In Clackamas County, on the Warm Springs Indian Reservation, sandy loam is present. In the Upper Deschutes River Area of Deschutes County, fertile sandy loam supports abundant crop production. Throughout the state the most productive soils are deep and well drained. They occur on the valley bottoms, close to large streams and rivers. The soils consist of materials that were carried by fast-moving flood waters and contain a large percentage of sand and silt.
Soil in the Willamette Valley of Oregon is remarkably fertile. Carried by floods and glaciers, the soil is deep and productive. The broad plain of the Willamette Valley is bound on the west by the Oregon Coast Range and on the east by the Cascade Range. The rich, loamy soil of the valley floor grows an abundance of varied crops. The Willamette Valley is composed of an old volcanic, sedimentary seabed that has been overlaid with silt, gravel, rocks and boulders that were carried by the Missoula Lake floods from Montana and Washington over 10,000 years ago. Red Jory soil, commonly found above 300-foot elevations is found in 4- to 6-foot layers and provides superior drainage. Soil found below the 300 foot elevation is composed of sedimentary-based soil.
Break up your soil to a depth of 12 inches using a spade, shovel, garden fork or tiller.
Fill a wheelbarrow with compost and move it to your garden.
Transfer compost in piles from your wheelbarrow to your garden using a shovel.
Spread the compost with your rake so that it covers the garden soil to a depth of 4 inches.
Turn the compost into the garden soil to a depth of 12 inches.
Water your garden deeply with a garden hose so that compost can soak into the soil.