We've started this innovative technique of testing the sap in our plants (very similar to a blood test in an animal) to see what's going on inside...
This is Leah taking leaf samples in our tomato field a few weeks ago.
We begin to sample at 7:00am so that the leaves can retain sufficient leaf-tension and moisture in transit. Each sample includes one set of 100 grams of young, fully developed leaves and one set of 100 grams of old, vital leaves. Each crop varies in how many leaves it takes to get to 100 grams: tomato leaves are quite small, so we need about 100 young leaves for 100 grams, and 50-60 old leaves for 100 grams. Zucchini leaves are so big that we only need 3-4 old leaves and 6-8 young leaves to reach 100 grams each!
Correctly identifying young, fully developed leaves vs. old, vital leaves is perhaps the most important part of the sap analysis sampling process. This is because some nutrients are mobile, some are partially mobile, and others are immobile. Nutrient mobility means that the plant can “move” the nutrient from old tissue to new tissue. Mobile nutrients include macronutrients like nitrogen, phosphorus and potassium; deficiencies of these nutrients in old leaves indicate that the plant has begun to move them from old to young leaves, which means the plant will soon need to be supplemented. Nutrients that are partially mobile and immobile include micronutrients such as copper, manganese, zinc and boron. Plants can’t “recycle” immobile nutrients, so we look for deficiencies of these nutrients in young leaves. The results of these tests give us a snapshot of what the plant currently has to metabolize for growth, which is a good indicator of what nutrients it will need in the near future. This allows us to amend our soil in time so that the plants are receiving exactly what they need, when they need it, particularly during the time when they are fruiting, since they expend a tremendous amount of energy and resources to produce fruit.
Leaves must be sampled very carefully as even the slightest amount of contamination will alter the results. We have to wear gloves, sterilize the scissors we use to cut the leaf, and place leaves into untreated paper bags. We cut each leaf right at its base to ensure that no petiole remains – since the petiole contains nutrients, it can influence what is going on inside the leaf.
Once the samples have been collected, we place each set into a ziplock bag and put the corresponding label on the bag. We have to pack the samples with icepacks to make sure the leaves survive the two-day journey to Ohio. There, Crop Health Labs repackages the leaves and overnights them to the Netherlands, where the analyses take place.
We sample each crop every two weeks. Depending on the crop, we sample three to four different times, which makes the whole process last six to eight weeks. Typically we begin to sample just before the plants begin to fruit, and then continue while it fruits. Results arrive one week after each sampling, which gives us time to apply organic amendments to our soil before the next sampling occurs. The results from the next sampling then show us whether or not our amendments actually helped the plants.
This year, we did sap analysis with our strawberries, tomatoes, zucchini, cucumbers, potatoes and we're starting on the fall brassicas...
A huge thank you to Leah for taking the samples for us all season. We really couldn't be doing this without her working with us this year. It's been fascinating to see how our plants respond to what's in the soil and what we apply. Farmers often think that if nutrients are in the soil (via a soil test) that they're in the plant. The next step for most farmers is to take leaf samples, but that only tells you what was going on in the plant a few weeks prior. And there is nothing to be done with that information - essentially it's too late to make any difference in the health of the plant. But with this real-time information provided by the sap test analyses, we are able to work with our plants to give them what they need, when they need it. And healthier plants produce healthier food for you!
We hope this wasn't too technical (or boring) for you! We think it's pretty cool and we're excited to share it with you!