Here is a great article on soil testing by Janet Carson with the UA Cooperative Extension Service.
Soil is an important part of growing a garden, yet it is often taken for granted. People spend thousands of dollars planning a landscape, buying the plants, but without a decent soil to grow in, the results, may not be what you had in mind. So lets get to the root of the problem.
Traditionally, Arkansans complain about the lack of soil, and the abundance of rocks. Or they may have "gumbo"–i.e., heavy clay, pure sand, or it’s so acidic, you could make vinegar from it. Fortunately, there isn’t a soil or planting site out there, that can’t be amended or corrected. It just may take a while. Learning your problems before planting, will make solving them much simpler.
Your first step should be to have a soil sample tested. This is a very simple process. Take a shovel and go six to ten places in the area you are planning to plant in. Dig down six inches –which may require a pick axe, but we do need a full soil profile. Then take a slice of the full six inch profile and place it in a bucket. Repeat this process six to ten times. By now, you have probably worked up a sweat, and gotten a great exercise workout. Mix this soil together, to get a good representation of what you will be growing in, and take a pint of it to your local county extension office. It should be relatively dry, since it will be shipped in a cardboard box, so let it air dry first.
If you will be growing distinctly different plants–such as lawns, vegetable gardens, perennials, etc, you can have several different soil samples tested. Simply repeat the same process for each one. A full pint of soil is needed for each sample you want tested. If you have a problem area in the yard, you may want an isolated sample from it to compare with the rest of the yard. Don’t divide your yard into too many samples, unless you plan to fertilize each area separately.
When you take your samples to the county extension office, they will ask you some routine questions to fill out the accompanying soil sampling form. In addition to the pertinent personal information, such as name and address, you will also be asked what you will be growing. If you are having more than one soil sample tested, you will also need an identifying name for each sample. Vegetable, lawn and flowers would suffice, just make sure you know what the name corresponds to, should you use something like 1, 2 or 3. Now all you have to do is wait on your report, which should be mailed to you within a week or two.
At this time, there is no fee associated with the routine soil testing process in Arkansas. Fees associated with fertilizer sales pay for this service.
When you receive your soil report, it may look a bit confusing. There are a lot of numbers and nutrients listed. There will also be a recommendation for the plants you are growing, as to fertilizer and liming needs. A fact sheet entitled "Understanding the Numbers on Your Soil Test Report" should accompany each soil test report. This should help to explain the level of the nutrients in your soil—what is high, and what is low, and even what some of the terms mean. Some people prefer to just follow the recommendations, and ignore all the numbers.
Some key items to look for include the pH of the soil. The pH of the soil is a measure of acidity or alkalinity, often referred to as a sweet or sour soil. Many soils in Arkansas are acidic, but knowing how acidic can determine your liming needs, if any. Many garden plants like slightly acidic soils, and some even prefer it–azaleas, gardenias and blueberries in particular. An optimum soil pH range for most plants is 5.8 to 6.3. Slightly lower or slightly higher isn’t a big deal, but some plants will suffer in soils with strongly acidic soils, while acid lovers struggle when it is higher than 6.5. If it has been determined that your soil sample is too acidic, there will be a recommendation of how much lime should be applied to get your soil in the proper range. Lime does not move quickly in a soil, so applying it prior to planting, where it can be tilled into the soil is ideal. If by chance, your soil is too alkaline, elemental sulfur or aluminum sulfate will be recommended to lower the pH.
Nutrients needed for plant growth are all listed in the soil report. They include phosphorous, potassium, calcium, magnesium, iron, manganese, copper and zinc. Nitrate-nitrogen and sulfate-sulfur are also there. On the soil report there will be a listing of each of these nutrients and a rate or level that they have been extracted from the soil, usually in pounds per acre. An example, for phosphorous: values below 20 are low, 20- 40 is moderately low, 40- 60 is medium, 60-80 moderately high, with 80- 100 being high. Again, the fact sheet will give you a comparison level.
Salinity or E.C. is another important consideration. Remember that all fertilizers are basically salts, and too much salt in the soil can cause injury to plants. This is also included on the report, and includes all soluble salts. If the readings are too high, there will be no fertilizer recommendations or fertilizer reductions until these levels go down.
There are other numbers and terms listed, which are important to soil scientists, and may stand out if there is a problem, but should not be of a huge interest to the home gardener. Knowing your soil pH is important, and getting your nutrient levels in line is also needed for good plant growth. If you have specific questions, call and visit with your local county extension agent.
If there are problems to your soil site, amending is important. But do remember, if you alter your soil with lots of organic matter or other amendments, it will change all your nutrient and pH levels, and it is important to test your soil again. Fall is an ideal time to test your soil, since often plants are nearing the end of their growing cycle, fertilization is ending, and you can prepare for next year in advance. Plus, you beat the spring rush, when everyone else is thinking about it.
This story first appeared in the AR Gardener Magazine.
By: Janet Carson
(Testing picture from http://blog.statcounter.com/2007/11/)