Soil testing can be one of the best things we do in terms of providing actionable data. Many turf managers utilize soil tests to determine what products to put down for the upcoming season and then never look at that soil test again. I think we can get more out of soil testing programs, but first I want to talk about a few of the basics on soil sampling. None of the data that we collect is meaningful if we aren't sampling correctly.
Here are the three most important rules when it comes to sampling:
1. Use a Consistent Sampling Depth - This is crucial. There is a debate on whether or not to sample at 4" or 6" depths. I generally recommend 4" sampling for fine turf, however, the depth is less important than the consistency of depth. If you choose 4", make sure that all sample cores are 4". Some shouldn't be 5" and others 3". There are a couple reasons for this.
Laboratory calculations and fertilizer recommendations are based off of knowing the weight of a soil. We always assume that an acre of soil 6" deep weighs 2 million pounds. From this we can calculate how many pounds per acre of fertilizer should be applied to achieve a desired increase in nutrient levels. If your depths are inconsistent, your recommendations will not be accurate.
Soils are stratified and not uniform throughout different depths. Layers of organic matter or immobile nutrients like Phosphorus can skew test results.
2. Collect a Representative Sample – Soil test reports are only as good as the samples used to generate them. If only small areas are sampled to generate recommendations for much larger areas, it may lead to the over or under application of fertilizers. I generally recommend pulling one sample for every 2,000ft2 or so with a minimum of 5 cores. Some may say that randomness is important, but representative is far more important than random. Pulling samples in a grid pattern can be acceptable although it isn’t random. I do recommend avoiding sampling the same locations every time soil tests are done.
3. Sample at the Same Time Each Year – Soils are incredibly dynamic and complex ecosystems that are constantly changing and evolving. All other things constant, we would still likely see different soil test results depending on whether we test in spring, summer or fall. I generally recommend testing in the fall at the end of the growing season, however, testing in early spring is acceptable as well.
When these two rules are followed, we generate meaningful data that can be tracked over time. This allows us to learn how grass on our site uses nutrients. Are there nutrients that we are accumulating over time? For example, if my soil potassium goes up year after year after year, that means I am applying more potassium than the grass can use. There are potential cost savings to recognizing this.
At FGS Consulting, we are passionate about helping our clients dial in their nutrient plans to ensure they are applying the right amount of fertilizers. No more, and no less. We’d love to see how our professional agronomist can help you develop the best fertility plan for your site.
Comments