By Darren Hefty
Soil sampling is so important for your profitability and future success. Here are 3 things you need to know when pulling samples this fall.
FIRST STEP: Choose a sampling technique.
- Grid sampling – divide your field up into equal squares (often between 1 and 10 acres – use smaller grids if there is more variance within the field). Send in a sample from each grid. This allows you to apply lime only where needed and to vary the amount of fertilizer you apply based on the potential productivity of the soil. Grid sampling is extremely easy to do with current technology. In fact, you can do it with your smartphone by using the www.farmlogic.com Soil Test Pro App.
- Zone sampling – divide your field up based on soil types or topography. This requires fewer samples to be taken compared to grid sampling. If you’re not sure how or where to start, you can always do grid sampling the first year and then combine similar grids into zones for sampling the next time.
- Composite sampling – using one or two samples for a whole field (field size 40 to 160 acres). This is by far the least accurate way of soil sampling and you often learn absolutely nothing about the field that will help you make your crop plan. For example, look at the picture of the grid sampled field. If you pulled half of the sample where the pH is in the 5’s and the other half of the sample where the pH is in the 7’s, you’d come up with a soil sample where the pH is between 6.5 and 7.0, which is ideal. In that case, you’d make no changes to the soil and continue to lose money. Composite sampling is mostly a big waste of time and money.
SECOND STEP: Pull good samples
When you are probing your soils, make sure you pull consistent samples. For example, if you are using a hand probe that’s fine, just go to the same depth every time. Also, keep your probe straight up and down rather than straight one time and at a sharp angle the next time. Pull several cores in each grid or zone and mix those together for the most representative sample. We encourage you to sample at the same time each year. Whether that’s fall or spring doesn’t make much difference most years, but if you sample in the fall, always sample in the fall. If you sample in the spring, always sample in the spring. This will give you the most consistent results and allow you to better compare soil tests from year to year. Finally, we love 0-6” samples, but it is nice to occasionally see 6-12”, 12-18”, and 18-24” samples in a few spots. Deep samples are important for many reasons, but they don’t need to be done in every spot in every field, in our opinion.
THIRD STEP: Choose a good soil lab
We use Midwest Labs in Omaha, but there are plenty of other good labs out there. Make sure you get soil pH, cation exchange capacity, base saturation (the base saturation numbers must add up to 100%), sulfur, and micronutrient tests. Once you find a good lab, stay there. That way it is easier to track the trends in your soil tests from year to year.