As we hit August, it’s time for all of my plant lovers to get serious about planning for the next few months. Regardless of whether you’re trying to plant vegetables, a wildlife food plot, maximize hay or forage production, or help your lawn and ornamental plants thrive, soil testing is a critical part of the process. I’ve written a number of articles over the last five years regarding soil testing, so you might be asking – why this again? Soil tests are used to determine the pH and fertility of soil and provides valuable information for adding lime and fertilizer. I thought I’d share a bit more about soil pH and why it’s so important this week.
When we talk about soil testing, most people think about fertility – nitrogen (N), phosphorus (P) and potassium (K) along with other micronutrients. However, if you speak with a soil scientist, we are often more concerned with soil pH. Soil pH is a measure of hydrogen (H+) and other acidic cations in the soil. The more acidic cations present, the lower the pH and more acidic the soil. Here in Lincoln County, the majority of soil tests we receive are acidic, with a pH of less than 6 (and often lower than 4.5-5).
Soil acidity is caused by a few major contributors. Soil composition, including the parent material it came from, organic matter content, and soil texture can all contribute to soil pH. Areas with heavy rainfall (over 30” annually) and water movement tend to leech basic cations (Ca, Mg, K, and Na) over time, causing the soil to become more acidic too. Finally, crop production and fertilizer use can also influence pH – removing crop materials from a property will reduce soil pH, increasing acidity, and the addition of ammonium-based fertilizers can also cause pH to drop.
The reason soil pH is so important is that it directly impacts the availability of nutrients to plants. At an “ideal” pH between 6 and 7, the nutrients most important for plant growth – N, P, and K, are freely available and the plant can take them in and actually use them. As the pH becomes more acidic, less than a pH of 5.5, the availability of N, P, and K declines – the plant can no longer access these nutrients, so they’re useless – even if they are present in the soil. Another thing that happens is that toxic nutrients like aluminum (Al) and manganese (Mn) become more available. This means that not only are the plants lacking the nutrients they actually need, but they’re also taking in toxic nutrients that decrease their ability to grow. At the proper pH of 6-7, these toxic nutrients are harder for plants to take in.
I bring all this up because most people focus on soil fertility (N, P, K) and disregard soil pH. Without proper soil pH, any money you spend on fertilizer is wasted, because the plants can’t access and use those nutrients. Soil pH has to be corrected first with the addition of a product that has the ability to bind to those acidic cations (H+) and remove them from the soil. While a lot of options for liming materials exist, the gold standard is powdered or granular agricultural lime. I occasionally get asked about liquid lime, wood ash, or other products, and while these may impact soil pH, they usually require applications of large amounts to make a noticeable difference, negating any cost savings compared to ag lime.
If you’re planning a fall vegetable garden, wildlife food plots, or trying to manage other plants on your property, August is a great time of year to run a soil test and build your plan for correcting pH and fertility issues. Soil tests are accepted by the Lincoln County Extension Office M-F, 8AM-5PM, and are $10 each. If you need assistance, call us at 706-359-3233 or email uge3818@uga.edu.
