How to sample

Guiding principles

What tests to do?

State the question you are trying to answer very clearly. The tests you need then should become clear.

1. What information will give you the ability to make decisions? What knowledge is needed?
2. The accuracy of the information you obtain is only as good as the accuracy of the sample. If you collect the wrong sample, you can’t get the information you need.
3. When doing organism assessments, what part of the plant will be most affected by organisms? When doing soil chemistry, what part of the plant will be most affected? Take samples in those places where the plant will be most affected, most rapidly, relative to what you think is most important.
1. Keep this in mind when looking at drip wells versus drive lanes, etc.
2. Soil surface sample, or 10 inches down?
3. Spring, summer, autumn, winter? What season tells you the most information? What season can you affect the plant most by altering organisms or chemistry?
4. How many sub-samples do you need to take to accurately represent what you want to know about?
4. There is a best soil food web, and a best foliar food web for each combination of crop type, climate region, soil type, amount of organic matter and water supply. The ideal food web balance for row crops in Arizona is different than the ideal balance for fruit trees or grapes in California.
5. For example, you want to know if your soil is healthy. That means a full food web analysis is needed, since you don’t know what part of the food web may or may not be "out of whack".
6. If you have done a food web analysis in the past, and know your soil lacks fungal activity, for example, then all you need to assess is fungal activity, and probably total fungal biomass. Perhaps mycorrhizal colonization as well, since this assay includes disease encountered on the root system, as well as insect feeding damage.