How to sample

Determining Your Sampling Area

Learn about setting the boundaries for your sampling

This goes back to the question, what do you want to know? You must decide what that is, and then we can help you decide where sample points should be placed.

1. For example, if you have areas that have poor plant production, or high disease incidence, you will want to sample each area separately.
2. If you have areas treated with different materials, and you want to determine the effect of each treatment, a non-treated area is used as a "control", a treated area is used to figure out the effects of a product, management, or disease on the food web or on soil chemistry. Then we know what needs to be fixed.
3. Another case is when one section of a field, or the farm has high production, or lots of weeds, and another doesn’t. Why the difference? This MAY be due to microbial differences in the soil, or in chemistry. SFI can determine if it is soil biology giving those differences, while a good soil chemistry lab can tell you if the reason is chemically based. Often, both will indicate changes, and most of the time, the biological assessment will let you understand WHY there is a difference.
4. Another example, does addition of kelp meal or ammonium nitrate grow better tomatoes? Take a set of three samples from the non-treated "control", the area to-be-treated with kelp, and the area to-be-treated with ammonium. This established whether the food web in each area started out the same, or if there were differences to begin. These differences can then be taken into account in statistical analysis. Apply the treatments, making sure to treat the control with the same amount of water as used in the treatments to apply the chemicals. Then take a set of three samples from the kelp area, and a set of three samples from the ammonium nitrate area after applying the treatments. You must decide how long after application you believe the treatments will have an effect, or sample with time to determine when the maximum effects were seen.
5. If you put the kelp on a sandy soil, and the fertilizer on a clay soil, comparing the two areas after treatment will show differences. But is it because of the kelp or fertilizer, or the differences in organisms between sand and clay soils? If you demonstrated that the food web was the same before doing any management in the two different soils, it is safer (but still questionable) to ignore the differences in soil type.
6. The same can be said for different plant types. For example, sweet peas and snap peas usually respond the same way to most management practices, and so extrapolating results seen in sweet pea to what we would expect in snap peas is usually safe. But there are differences in the species of bacteria and fungi around the roots of these two different plant species. Thus, it is possible that each plant species will react differently in some situations. We haven't found those situations yet, but they will be discovered someday. So, extrapolation is probably safe, but not entirely safe.
7. Extrapolation of results across any grass species is not acceptable. Different grasses do better when the soil food web has nearly a 1:1 ratio of fungi to bacteria, while bunchgrasses do better with a ratio closer to 0.5. We can use these differences to select for one grass species over the other. Therefore, results observed from a sweet corn trial cannot be extrapolated in exactly the same way for field corn.

How long after applying treatments should you assess the foodweb?

1. If you want to know the immediate, direct impact of the treatment, take samples 3 days after applying the treatments.
2. If you want to know the short-term outcome of all the interactions started by applying the treatments, sample after 7 days.
3. If you want to know the effect on longer-term, plant-responses, sample at 1 month (especially for mycorrhizal colonization, you must want this long), or longer.
4. To monitor effects of all treatments or management from year-to-year, sample once a year at the same time each year.