Where to test: choosing sample points
Since you cannot test all of the soil at all of your project sites, you will need to select a few places to test. This is called ‘sampling‘.
The exact locations where you will do the tests are called the ‘sample points‘. A key principle is that each time you test, you will do the tests at the same set of sample points, so that you can track changes to that soil over time.
The method for choosing your sample points is called the ‘sampling pattern‘. To get meaningful data from your soil sampling, it is important to choose a sampling pattern and depth that fit your objectives. There are three basic pattern strategies: random, grid or zone sampling. We recommend using the Zone sampling strategy, which is good for projects where we want to monitor our efforts over time.
Zone Sampling Strategy
If you already know parts of the field that behave differently (due to soil type, past management, terrain, or yield history), divide the field into a few “management zones.” Then, sample each of these zones separately by taking a soil sample composite from it. Zone sampling uses existing knowledge – like soil maps or yield data – to draw boundaries.
Examples of zones: [XXXXXX to be added by PI team]
Action Learning: Identify the different zones in the land that your project covers.
You could draw a sketch map of the site(s), or use an existing base map, and mark the zones. Seek input from people that know the ground well – project participants or field staff perhaps.
How do I choose where to sample?
Sampling points should be representative of the different zones that the project covers, and be accessible over time.
Our advice is to focus on as many sampling points (per zone) as you can realistically keep track of. In other words, the number of sampling points selected depends on your capacity for monitoring.
Generally, more sampling points means more significant results, but it also means more effort (time and resources) are required. We advise starting with a few zones (and sampling points) first, and gradually expanding so that the whole project area is represented.
If there are 10 zones, select the 5 most important ones, and define at least 2 sampling points in each. In subsequent years you can do the same for the other zones, or increase the number of sampling points per monitoring area.
Action Learning:
[XXXX to be added by PI team]
How to record your chosen sampling points (when in the field)
1) Mark the location: GPS or name it and mark it (to be able to come back)
When defining sampling points, mark these physically (using sticks and labels) and digitally by recording their geocoordinates and depicting them in the digital polygons/map of the project site.
2) Take a photo at the same location, same direction (a ‘point photo’). It will also allow us to see the vegetation and its evolution.