ZONE SOIL SAMPLING
Zone soil sampling is a form of sampling that uses management zones to gain a better understanding of soil fertility. To clarify, by dividing a field into zones that respond similarly to applied fertilizer the soil test results are more consistent and accurate. Because fertilizer prescriptions rely on good soil test results, they also become a better custom fit for the field.
Agronomists will tell you that collecting soil test results over time adds value. That is to say, watching the nutrient level trends move as crops cycle through the years, is as important as the value of the soil test itself. Crop consultants dive deep into understanding why zones respond differently than other.
Similar to any other management zone, soil sampling zones should start simple and evolve over time. For example, zone samples may start by following terraces and waterways. These basic features are are easy to group into simple management zones. This is a pretty common practice that originated from the soil sampling methods many universities have taught for decades.
A zone soil sample is basically the evolution of the composite soil sampling method. Originally, we had features that were easy to see like drainage but with today’s technology the layers available have expanded. For example, soil texture mapping and yield analysis provide many added layers to base management zones on. Finally, the key is to refine the boundaries of the zone as you learn more about the field.
Zone samples can be captured with GPS as points or as polygons. After sample zones have been created a decision has to be made. There are at least two methods that could be used:
- Collect random soil sample cores within each of the zones.
- Drop a point for each spot where soil sample cores will be collected.
Some crop consultants prefer to use points in order to pull samples from the same locations year after year. The result is a very consistent soil sample.
On the other hand, other consultants prefer to randomly sample within the zones. Similar to the traditional sampling method universities have taught for years. So, the debate rages on as to which method is better than the other.