Importance of Soil Sampling: Starting with an understanding of what to work with

In order to make decisions for inputs on the farm, it all starts with the ground. To feel more informed in making confident decisions we enlist the help of soil sampling and running requested lab tests to educate ourselves of what exactly the ground is made up of. When soil sampling every step counts. From the environment that an individual is sampling in to how the soil is packaged and sent to the lab to be tested. Consistency is key in order to get the best possible results when testing.

In the north country of Minnesota here, we have to take into account seasonal effects of soil and also crop effects of the soil when we get test results back and are questioning some things. Most specifically potassium and pH values. In high clay soils, which we have plenty of here in Minnesota. Potassium has a tendency to be higher in the winter months due to freeze and water effects of nutrients. Crop effects also influence exchangeable potassium as potassium is a mobile nutrient that is trucked by rubidium to the plant.

Most commonly potassium will test lower following corn than following soybeans because there is a larger uptake of potassium by corn rather than soybeans. Keep this in mind as well when looking at results. When testing for values of pH it can vary depending on nitrogen and sulfur inputs, rainfall or soil buffering capacity. Keeping that in mind when looking at pH results that there are many factors that influence it and it is not a fixed value.

Soil sampling does differ within farming practices. Conventional farming samples are commonly taken in the 0-6” range. Minimal tillage, ridge till and no till samples should be taken 0-3” and then again at 3-7” to properly assess the stratification that is occurring in order to modify fertilizer and soil amendment rates, timing and or placement. The next decision is to sample in grids or zones. There is debate over which is better, but I believe it is a situational decision. It depends on what the goals for each specific field is and also what the pocket book is able to do with such projects. Grid sampling can carry a hefty bill with it for arguably the same information that you would get with zone sampling but in smaller areas. Where zone management sampling is economic and you still get “a look” of what the field is. Again, it comes down to what the goals are and the information wanted. There is no wrong answer. There just has to be educated answers to make decisions for each individual farm.

Soil sampling is the starting line for every input decision and crop decision for each farm and each field. The most valuable tool that is almost undervalued. With this tool it forces to take a step back and gives a visual to look at what needs to be dialed in and what does not. I also highly suggest that if you don’t quite understand the results, to reach out to someone who can help. Always ask questions in order to get a full understanding! Happy farming!