Soil testing is a somewhat broad term used to describe one or more methods of soil analysis, which can be conducted for a variety of reasons, including estimating the amount of available essential plant nutrient elements in the soil, or for engineering purposes, in order to learn more about the ground conditions at a building site.
In agriculture, soil tests are primarily performed to determine the amount of available plant nutrients and the pH levels of the soil, as well as the soil composition. When conducting soil testing on farmland, you’ll want to take around 10-20 sample points per 40 acres of growing field. Soil tests can show different results depending on the location and depth of the test. Some parts of the field may show completely different results from other parts of the field in terms of soil composition, nutrient levels and pH levels, so it’s important to take several samples to get a clearer picture of the overall fertility of the soil.
When taking soil samples it’s important to know that the soil chemistry may change between the time the sample was taken and the time it’s analyzed in the lab, so ideally, the soil sample should be analyzed within a 24 hour period from when the sample was taken. If it’s not possible to have the sample analyzed within 24 hours, you can freeze the sample until you can get it tested.
So, what exactly happens to the soil sample when it reaches the lab for testing? Most commercial labs tests soils for plant nutrient levels, including primary nutrients like nitrogen (N), phosphorus (P), and potassium (K), as well as secondary nutrients like sulfur, calcium, and magnesium. Minor nutrients like manganese, iron, zinc, copper, chlorine, boron, and molybdenum can also be detected and measured. Soil tests can also determine the pH levels of the soil, which is an important factor for plant growth.
There are many commercial labs that perform these types of soil tests. A quick internet search can help you find a local lab to take your samples to. There are also DIY tests you can perform yourself that test for the major nutrients, as mentioned above, as well as pH level. These can be purchased at many farming co-operatives, hardware stores and gardening centers. DIY soil testing kits generally range in price from $25 for a simple test kit to several hundred dollars for more advanced, electronic testing kits.
The information that is revealed by a soil test can help you determine what crops might perform best in your field. Soils low in pH and low in essential plant nutrient elements may need to be amended to balance the pH and increase the nutrients available. Agricultural lime is often used to alter the pH level of the soil by increasing the pH level to make the soil less acidic. Crushed limestone is largely made of calcium carbonate and some magnesium carbonate, so adding lime to increase the pH level will also add these two secondary nutrients.
Advancements in technology have also allowed growers to get a better idea of the variations in plant nutrients levels, water drainage and ground temperatures in their fields. Known as precision agriculture, it allows growers to identify any problem areas in their fields, which they can then treat as needed. This not only saves money (you only apply amendments where they are needed as opposed to the entire field), but it also provides detailed maps of the fields that can be used for other purposes, such as the use of autonomous tractors and harvesters.