By Tim Daly
Soil testing helps you know the pH and nutrient levels of your soil though plants do not need soil to grow; however, soils store the nutrients, air, heat, and water plants need in order to thrive. Soil is actually a living, breathing mixture of a multitude of minerals, organic matter, and water. Soil is a source of support for the plant roots and holds the moisture and necessary nutrients for plant use. There are many soil types, and they differ in texture, structure, pH, nutrient and water holding ability.
Texture is the finess or coarseness of the soil particles and it refers to the relative proportions of different size soil particles. The smallest size is clay, followed by silt. And the largest particle size is sand. You can determine the presence of the three types by rubbing a small amount of moist soil between your fingers. Sand has a gritty feeling, silt is greasy, and clay has a slippery feel. Clay soils contain more nutrients than sandy soils since they have greater surface area. If fertilizer is applied to sandy soils, it may be immediately available, but will leach out rather quickly. In clay soils or sandy soils with organic matter, such as compost, added to it, the nutrients will adhere to the surface of the soil particles and are less likely to leach out. Organic matter has a positive effect on the structure and texture of the soil by increasing the nutrient holding and water holding capacity of sandy soils, as well as improving the drainage and workability of clay soils.
Plants require several important nutrients for growth. The macronutrients are the ones they need most, and are nitrogen, phosphorus, and potassium. The secondary nutrients, which are needed in lower quantities, are magnesium, calcium, and sulfur, where as the micronutrients are required in very small amounts, and they are zinc, iron, manganese, and a few others.
One of the most important components of soil fertility is soil pH, which refers to the acidity or alkalinity of the soil. pH is a scale of 0 to 14, with 7 being neutral. Below 7 is acidic and above 7 is alkaline. The scale is logarithmic meaning a pH of 6 is 10 times more acidic than 7, and a pH of 5 is 100 times more acidic, and so forth. Soil pH is important because it has a pronounced effect on nutrient availability in the soil. A majority of plants thrive in soils with a pH of 6.0 to 6.5. However, some plants, such as azaleas, rhododendrons, and blueberries, require a lower pH of 4.5 to 5.5.
A soil with a pH that is too acidic or too alkaline will lead to nutrient deficiencies. The nutrients become insoluble and unavailable to the plants from the soil when the pH is incorrect. However, iron and manganese are more available at lower pH, and that is why some plants need to be grown in a more acidic soil since they have a higher iron requirement.
How to take a soil sample: say you have a lawn of bermuda grass. You need to dig down four to six inches with a small shovel or soil probe in many different areas of the lawn since the soil pH and fertility can differ significantly from one end of the lawn to the other. Put the sample cores in a bucket, mix them together, and then take a small sample, perhaps six ounces or so, and place into a plastic bag. Bring the sample into the Gwinnett County Extension office, located 750 S. Perry St. Suite 400, Lawrenceville, GA 30045. There, you will obtain a small sample bag, fill out your contact information and the type of plant material being grown, and then place the soil sample into it. For a fee of $8.00 per sample, it will be sent off to the University of Georgia Agricultural and Environmental Services lab for analyses. You will receive the results in 7 to 14 days by mail or e-mail.
Soil testing allows you to know the pH and nutrient availability of the soil for your plant material, and can save money on fertilizer and lime. For more information on soils and soil testing, please contact the Gwinnett County Extension office.
Timothy Daly is the Agricultural and Natural Resources Extension Agent with Gwinnett County Extension office. He can be contacted at 678-377-4010 or timothy.daly@gwinnettcounty.com
