Many people understand the basics of soil sampling but here is something most never think about, sticking with a lab. I have submitted around 175,000 soil and forage samples in my career and most have went to two different labs and there is a reason for this. There are 1000s of forage and soil testing labs across the US and they they have different calibrations, testing procedures and standards. In the case of soil sampling, there is the standard samples as well as the Haney Method.
If I took 10 soil cores per spot and 10 different spots per food plot and sent the cores to 10 different labs, the results would vary. The results in itself are not a be all end all. What I always look for is change or “benchmarking.” I am looking for if your nutrient levels are moving down, moving up or staying relatively balanced. There can be variation in soils across one field. There can be differences in nutrient levels, depending on the time of year. There can be differences and anomalies with how one samples a fiend. For example using shovel versus a soil sampling probe can lead to different values. Whether you take 6 samples per field or 10 samples per field makes a difference.
So many people sample in the spring but most farmers fall sample once the crops have ceased growing. Let’s say you had a previous years soil sample and planted soybeans this year. You put down 300 pounds per acre of 9-23-30 fertilizer. You hoped for 50 bushels of soybeans per acre. What happens if you had a drought and the growth and yield were much lower than expected. Many don’t consider that the plants might have only uptaked ½ the nutrients you put down. We might have an existing build up of nutrients because of the growing season. Knowing this, you now have some months to work with your food plot advisor to decide on a nutrient program based on the intended plot to plant the next growing season.
When I work with clients, I try to get past soil samples and compare them to current values. I also try to get people to take plant tissue samples, as that is “reality” where as soil samples are more a baseline or benchmark. In my case I always look to soil sample and compare them to the plant tissue samples. In the end, choose one lab and try to stay with one lab. If you switch to a new testing lab, I’d recommend getting another set of samples within the first 12 months, then you can choose to wait another 2-3 years to collect new samples.
Food for thought. I’m happy to answer any questions.