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Physical Properties of Soil
The physical properties of soil in a lawn are made up of soil "horizons", or layers of soil. There are several types of soil horizons found. Soil horizons can be predominately made of organic material, mineral layers, or layers of hard bedrock. The soil color is also a physical property. If you've ever taken note of the different colors seen in soil, you may have noticed that soil can be dark brown, red, yellow, or even gray. These colors can be caused by the amount of iron in the soil. The texture of soil is also important when determining the physical properties of soil. Soil contains sand and silt in various amounts. Sand and silt are considered to be inactive, since they can't retain water or nutrients. Clay is considered to be active, because it does absorb water.
Soil structure is formed from peds, or units of soil that repeat themselves in certain ways. Soil structure can be granular, prismatic, columnar, blocky, or platy. Some areas of soil are actually without structure, and are referred to as massive or single grain. Massive soil is very compact, and can be made mostly of clay, being void of proper aeration. Single grain often occurs in very sandy soil, where nothing holds the soil together. This soil is not very fertile.
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Chemical Properties of Soil
Elements like hydrogen, aluminum, potassium, magnesium, and calcium make up the chemical properties of soil. These provide nutrients in the soil that help nourish the plants that grow in it. Soil has a pH, or degree of acidity or alkalinity. A pH of 6.0-6.8 is best for growing plants because the absorption of nutrients is best at this pH. Testing the current pH of the soil in your lawn will give you an indication of whether or not your soil is at the proper pH. Any local garden center can test a soil sample for you. Test kits are also available. Fertilizing soil can adjust the pH of that particular soil, making the solubility of nutrients more optimal for growing gardens. Depending on the current pH of the soil, different chemicals are needed to optimize the soil. Adding lime to soil will increase the pH, while adding sulfur will decrease the pH. Depending on the type of soil you have, you will adjust the amount of lime that you add to increase the pH of your lawn. If you have sandy soil, add 4 oz. of lime per square yard of lawn. For clay soils, add 12 ounces of lime, and if your lawn is made up of peaty soil, you'll need 25 ounces of lime.
Knowing the properties of soil in a lawn may just make the difference between a weak, brown, patchy yard, and a lustrous carpet of emerald green grass. Know the soil in your lawn, and you can make the most of it, producing grass to be proud of this summer.
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1. US Department of Agriculture: http://www.nj.nrcs.usda.gov/partnerships/envirothon/soils/soilproperties.html
2. The Garden Helper: http://www.thegardenhelper.com/acidsoil.html