Plant growth is dependent upon several nutrients. Having a soil test performed on your garden soil will tell you how much of these nutrients are in your soil. Typically a soil test report will indicate the level of nutrients in your soil and the pH value. The report will also make recommendations for things you need to add such as the amount and type of fertilizer or lime. Armed with this information you can customize the fertilizer and / or lime applications for your specific plants or vegetables. By following these instructions you can reduce issues with under or over fertilization.
Recommended Method of Soil Sampling
To prepare a sample of your soil for testing you should take at least 12 samples down to a 6 inch depth. Soil samples from lawns only need to be taken to a depth of 2 or 3 inches. Thoroughly mix these samples in a clean bucket or container. Do not use a container that may of any residual fertilizer or pesticides in it as this will alter the results of the test. Allow the sample to dry out before preparing it for shipment to the lab for testing.
Each sample should be at least 2 cups of soil. Extension agencies offer many types of analyzes for soil so be sure to mark off what you want properly on their forms. Typically they will ask what you are planning to grow in the soil the sample came from.
What the Soil Test Will Provide
The soil pH value.
The current soil levels of phosphorus, potassium, calcium, magnesium, zinc and manganese.
Fertilizer and lime recommendations (if needed) for the plants you are growing.
How Many Samples to Take and When
Plants, vegetables and lawns require different levels of nutrients for best growth. This means you should take separate samples from each of these areas. It is generally recommended to take a soil sample every year. This can be done at any time but for the best results take your samples a few months before planting or establishing perennials. For lawns you should sample a few months before the recommended fertilization time. This will allow time for the fertilizers and soil amendments to react with the soil.
Soil Test Results
Your soil test report may vary depending on the laboratory performing the test. If you have gone through your county Extension office they will most likely receive a copy of the report also.
Some soil test reports will have a bar graph representing the amount of soil nutrients found and the soil pH value. One section shows how much lime (if needed) to add for each 1000 square feet and refer you to specific comments. The comments page will tell you what type of fertilizer you need, how much you need and how to apply it. These recommendations are specific for whatever type of plant you want to grow, based on your selections when submitting the sample for testing.
Your Soil Test Report
Soil pH: The soil pH scale runs from 0 to 14 and measures how acidic or alkaline the soil is. A soil pH of 7 is neutral while numbers below 7 indicate acidic and numbers above 7 indicate alkaline. Nutrient availability is directly affected by soil pH. Plants perform best in different soil pH ranges. Acidic soils, pH levels of 5.0 to 5.5 are ideal for azaleas, rhododendrons, blueberries and conifers. Slightly acidic soils, pH levels of 5.8 to 6.5 are ideal for vegetables, grasses and ornamentals. Soil pH values above or below these ranges may result in less vital growth or symptoms of nutrient deficiencies.
Nutrients: There are three categories of nutrients for optimum plant growth: primary, secondary and micronutrients. The primary nutrients, nitrogen (N), phosphorus (P) and potassium (K) are needed in larger quantities compared to the other nutrients. The secondary nutrients, calcium (Ca), magnesium (Mg) and sulfur (S) are required smaller quantities but are still essential for good plant growth. Plants only require very small amounts of the micronutrients which include zinc (Zn) and manganese (Mn). Maintaining the soil pH at the proper value will correct most deficiencies of micronutrients.
Nitrogen: Nitrogen testing is not recommended because the levels of available forms of nitrogen are very water soluble. The available nitrogen moves quickly through the soil with rain and irrigation. This causes fluctuations in the amount at the roots of the plants. The recommendations for how much nitrogen needed are based on the type of plants you stated were being grown in the sample tested.
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