Intensive grid soil sampling is the base for any good soil fertility program. The vast majority of the acres in this area are grid sampled every four years and the information is used in the basic and advanced discussions on how to best manage inputs.
Does Time of Year Matter?
Grid soil sampling can be done any time the ground isn’t frozen or when a person can effectively get through the standing crop and still sample effectively; however, is there a certain time of year that is better?
From an agronomic standpoint there can be some differences in sample results depending on the time of year a sample is taken. Potassium, in particular, can be impacted by soil moisture at the time of sampling and by the tie-up of potassium in plant stover. In dry fall conditions the results can be skewed as discussed in this ISU Extension publication. Therefore in those dry scenarios, after plant sampling can actually provide more accurate results.
The best agronomic recommendation for timing is that once you move to an after plant sample is to keep the sample rotation with that same timing moving forward to get the best comparison information.
What Size Grid is Ideal?
Generally, the more intensive the soil sample, the more accurate it becomes. Regular composite sampling without the use of GPS or grids is a method that will average out whatever area that sample is taken from, often these are 20-40 acres in a normal soil sample. Once you move to grid soil sampling, the standard sizes start with 10 acre grids, then 4.4, 2.5, and 1.1 acre grids. There are differences in accuracy;
- 10 acre grids are 50% more accurate than a composite sample
- 4.4 acre grids are 70% more accurate than a composite sample
- 2.5 acre grids are 90-95% more accurate than a composite sample
- 1.1 acre grids are 95+% more accurate than a composite sample
Usually 10 acre grids are not used for variable rate fertilizer or lime applications because they are simply too large of an area to average the sample and reliably apply any variable rate nutrient. Once samples are moved to the smaller sizes, then it becomes a matter of weighing economics vs. agronomic. Well over 75% of the grid samples taken are 2.5 acre grids which are quite a bit more accurate than a 4.4 and tend to be cost effective. The standard timing is to resample every 4 years, however with the impending large input price increases on the horizon, there are some sampling every 2 years to enhance the decision making.
Does Method Matter?
Quality soil sampling is key to getting good results. At FCS we partner with SoilView to do our sampling services. This video showcases how the SoilView sampling method ensures the highest quality.
Sample Now, Pay in January 2022
At FCS, we can grid sample your field and your won’t have to pay until January of 2022! This allows to get the sampling complete and get the results in advance of any fall application.
Contact your trusted FCS Agronomist with any questions.