Soil testing is an essential part of understanding any landscape and providing proper care. Soil tests can reveal the soil pH levels, macro nutrient levels, micro nutrients, and organic content with a reading on microbial activity. If a lawn is to be maintained organically then these readings are even more critical and should be performed more frequently than with a traditional lawn care regime. There is some confusion in the proper way to test soil and where to take soil for testing, but it can be done very easily and usually at no to low cost by following these steps.
Step 1: Pull soil cores from many points in the lawn to be tested
To take a good reading soil must be tested from several spots throughout the property. One location may result in a deceptive reading if that particular spot has, for instance, an excess of nitrogen. Pull cores from eight to twelve points in the lawn. Try to get a mix of all of the conditions existing in a landscape. Cores should be pulled from about two to three inches deep, where the roots are actually growing. It will do no good to just test the top layer of soil. Ideally the soil should fill up around half of a one quart zip lock bag.
Once the soil is placed in a bag remove any debris such as grass, moss, sticks, or other surface organic matter. Removing all debris is necessary to get a good organic soil content reading. Most tests produce an organic content reading by weighing the soil then burning it and weighing it again. Organic matter will burn off, because it is carbon based, leaving a clear amount of organic material defined by the before and after weight. If grass clippings are left in the soil it will throw off the test by creating more before weight.
Step 2: Find a testing location
Most state universities have a cooperative extension or agricultural dept. that tests soil at little to no charge. Due to the test being low-cost it can take a few weeks for results but worth the wait because the testing done is very comprehensive and easy to read. Here is a link, to the UCONN co-operative extensions soil testing page with their guidelines. In the future I will post a link to each states page, until then you can search engine your respective universities agricultural department.
Another faster but paid solution is agricultural stores. Most offer paid soil testing. The most notable store in the northeast is Agway, here is a link to their page. The paid testing has a variety of test options from just pH levels to the full test of everything from soil type and composure to CEC and more. The tests vary in price and can be expensive if you are not careful, hopefully you are near a university in your area and have the time available to wait for the test to be performed.
Step 3: Reading your test results
The test is not too confusing, just read it line by line. A test will tell things like pH level and how much lime to apply to achieve neutral. Some nutrient levels are rated in a verbal scale, for instance potassium is rated from very low to very high, and then corrective action is left up to the applicator discretion.
A list of the potential readings are as follows:
- Nitrates- Nitrogen is rated from low to high and is used by a plant to stimulate growth.
- Phosphates- Phosphorus is used by plants for seed germination. There is much controversy surrounding the use of phosphorous and even full bans in place in some states see here for more info . It can cause many problems in water sources and should only be used when seed germination is desired, even if a soil test reflects low amounts.
- Potassium- Potash is a salt that helps plants retain water and is used to help store carbohydrates in the roots. It will return a value from low to high on a soil sample.
- pH- Soil pH tests levels on a numeric scale from 1 to 14. 1 thru 6.9 is acidic and 7.1 thru 14 is basic see image below. A perfect 7 is neutral, turf grass likes to be in the range of 5.5 to 7 and if you are there corrective action is not necessary. However if you do need to change pH levels, lime will raise your pH and sulfur will lower pH. Most soil tests recommend the amount per thousand square feet that should be applied.
pH is an important metric because certain nutrients become available depending on the soil acidity. I have included an image below with a scale of optimal pH levels for certain nutrients.
- Organic Matter- The amount of organic matter is important for the natural sustainability of your landscape. Organic microbes produce nutrients on their own and can naturally feed your lawn. Also all organic fertilizers are dependant on microbial activity to break down the fertilizer and convert it to a usable nutrient, so organic gardeners and lawn care professionals must pay close attention to this value. Organic matter is usually rated from low to high.
How often should testing be done?
Soil tests can be performed once every three years in ideal conditions. Of course it depends on the property, results desired, and the customers budget but that being said three years is a good benchmarking period. If you are trying to move a particular value, like pH, remember that it can take years for lime or sulfur to have an impact. Just be patient and follow the appropriate course provided by your soil testing.
Have you had any experience with soil testing? Is there something I missed or that you feel needs to be said? Then please join the conversation and comment below. Thanks for reading.