Soil acidity a very important environmental factor that can affect plant growth, and limit your crop production. Some plants such as azaleas and camellias are acid-loving, while others such as clematis prefer a much more alkaline soil to call home.
Soil acidity or alkalinity is defined by the amount of calcium-rich lime in the soil and the type of soil itself. Soil acidity and alkalinity are expressed by their pH; a pH lower than 7.0 connotes an acid soil while one with a pH higher than 7.0 is alkaline.
As a rule, soils found in moist climates tend to be more acidic while those in dry climates are more alkaline. For maximum plant growth and health, you must adjust your soil to suit the acid needs of the plants you plan to use.
Soils can be acidic because of the composition of the parent material (rocks) from which they were formed. Or it becomes acid via a number of processes. Cropping and use of nitrogen fertilizers are two main sources of soil acidity while another contributor is rainfall.
Crop Removal: Calcium, magnesium, and potassium are essential nutrients for plant growth. Plants naturally remove these nutrients from the soil and they are also remove through harvesting. This can leaf to an acidifying effect on soil.
Fertilizers: Nitrogen fertilizers have a greater acidifying effect on soils than other fertilizers. Two processes are involved. First, commonly used nitrogen fertilizers contain ammonium nitrogen. Soil bacteria convert ammonium to nitrate (through a biochemical process called nitrification. Hydrogen is released and free hydrogen ions cause an increase in acidity. The second acidifying effect comes from nitrate that is not taken up by the growing crop. Nitrates are very soluble and, if not consumed by plants, will move downward with soil water and may be carried below the root zone. They take with them other nutrients that have a positive charge, most likely calcium and magnesium, and their removal in this manner has the same acidifying effect on soils as removal by a crop.
Rainfall: Soils can become acid even in the absence of crop removal or fertilizer applications. Rainfall is considered a natural cause of acidity because of the downward movement of water through the soil and the removal of nutrients from surface runoff and erosion.
Most garden supply centers sell soil testing kits, and some will even test a soil sample for you. Also, if you live near a university with an agricultural extension, your chances of getting a professionally conducted soil test are very high.
If you go the soil pH test kit route, your kit will probably consist of a test tube, some testing solution and a color chart. Put a sample of your soil in the tube, add a few drops of test solution, shake it up and leave it for an hour or so to settle.
The solution in the tube will change, after which you can compare the color of your sample with the color chart that came with the kit to determine the pH of your soil sample. Higher end soil testing kits also usually include a booklet that will tell you how to interpret the results of your tests.
When you’ve identified the pH of your soil, you can change it to be more acid or alkaline depending upon the result your test obtained and the soil needs of the plants you want to plant. Usually, it’s easier to make soils more alkaline than it is to make them more acid—and because different soil types react in differently to added lime, clay soils and peaty soils require more lime than sandier soils.
Making highly acidic soil more balanced can be a lengthy project. It’s better to test your soil each year and make the indicated adjustments gradually. In addition to lime, adding hardwood ash, bone meal, crushed marble or crushed oyster shells will also help to raise the soil pH.
If your soil needs to be more acidic, you can use sulfur to lower the pH. Mix the sulfur thoroughly into the soil before planting. Sawdust, composted leaves, wood chips, cottonseed meal, leaf mold and peat moss will also lower the soil pH.
New gardeners rarely understand the whole issue of pH soil balance, but as you become comfortable with your new hobby and want to introduce a wide variety of plant species, it is important that your soil condition are optimal for your garden plants. For many, the process may seem complicated but it really needn’t be. Just test your soil conditions once a year and then either plant in that area according to the soil, or adjust the soil conditions to meet the needs of your existing plants.
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Remember:
A soil test determines the soil pH. Soil pH indicates the acidic level of a soil. A pH less than 7.0 indicates an acid soil.