Ag Geek Speak

6.5 Tiny Bytes: Plant Tissue Testing 101

• A Podcast for Precision Agriculture Geeks • Season 2 • Episode 6

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Plant tissue testing offers farmers and consultants valuable insight into crop nutrient status and helps diagnose field issues when properly conducted. We explain the science behind tissue testing and share practical tips for getting actionable results.

• Tissue testing can help to evaluate nutrient status to understand crop health at various growth stages
• Troubleshoot field issues by comparing samples from healthy and problematic areas
• It is important to sample the correct plant part according to the crop's growth stage
• Mobile nutrients show deficiency in lower leaves while immobile nutrients affect upper leaves first
• Remember to remove soil contamination from samples, especially when checking iron levels
• Tissue tests can help to identify the problem while soil tests help determine corrective actions
• Have a specific goal in mind before collecting tissue samples
• Take both tissue and soil samples when diagnosing nutrient deficiencies


Jodi:

And now it's time for a Tiny Byte of knowledge. Okay, what is three plus seven?

Sarah:

Jodi, what are you doing with that corn plant?

Jodi:

Wait, wait, wait, wait. It's going to give me an answer. I'm giving it a tissue test.

Sarah:

You're giving the corn plant tissue a mathematical test. Yes, Jodi, that is not a tissue test. What is a tissue test? A tissue test is simply taking a part of a plant and we dry down that plant part and we grind it up and we literally test it to see how many nutrients are in that plant tissue. Oh so, jodi, let's get to the brass tacks here and talk about the real topic of today's tiny bite. Why would we do a plant tissue test? What are the reasons for plant tissue testing?

Jodi:

There's a couple of really good reasons to go out and test plant tissue, and one of the first one is just to evaluate nutrient status. Right, so figuring out, at this part of the growing season, what is the nutrient content, what is my nitrogen status, what is my sulfur status? How is my corn plant or my other crop holding up at this part of the growing season? What is the nutrient content? What is my nitrogen status? What is my sulfur status? How is my corn plant or my other crop holding up at this point in the growing season? I think really the most valuable way that we can use tissue tests is to troubleshoot issues in the field.

Sarah:

I don't know if you've ever seen situations where you got a yellow blob in the middle of the field and the rest of the field is green.

Jodi:

Absolutely.

Sarah:

Absolutely.

Jodi:

Yeah, I mean some of these. These things just pop up. Sometimes it's a it's an herbicide issue, maybe it's SCN, you don't. Sometimes you don't even know where to start, and so a fantastic way to help figure out what's going on is doing a plant tissue test, where you've got a good plant tissue test versus a bad plant tissue test from that area in the field that looks different from everything else.

Sarah:

So when you're doing plant tissue testing then just to emphasize that point when you're troubleshooting you are usually taking plant samples from both the good area in the field as well as the bad area and then comparing those results at the end to see what kind of differences are going on in the field.

Jodi:

If you're really confident that okay, I'm looking at a nutrient deficiency here, then sure you can probably get away with just doing a good plant tissue sample. If you're trying to figure out an unknown is this herbicide and you're trying to rule out things, it's really important to have both that good and bad sample, just so you can compare those numbers to each other.

Sarah:

There are definitely some things to keep in mind when you're out tissue sampling. First of all, you need to make sure that when you are taking that plant tissue sample, that you are sampling the right part of the plant for the stage that that particular crop is in. And usually when you're working with a specific lab, they're going to have guidelines as to what plant part you should be sampling at different times of the growing season.

Jodi:

Let's think back to a couple of tiny bite episodes ago and which we'll link it out in the show notes. But, like we talked in the episode, plant nutrients can be mobile or immobile and so if we're looking at nitrogen at the seedling growth stage of corn, if we're collecting from different parts of that plant, from the lower leaves to the top part of the leaves, the nutrient content in each of those individual leaves that you're collecting from different parts of that plant, from like the lower leaves to the top part of the leaves, the nutrient content in each of those individual leaves that you're collecting from the top of the plant to the bottom of the plant, is going to vary.

Sarah:

Absolutely so. For example, nitrogen, a plant mobile nutrient, and so the deficiency symptoms show up first at the bottom of the plant. If you sample that lower plant tissue on that plant, you're going to have less nitrogen in that concentration than at the top of the plant. Inverse, if you were to be in an iron situation where you've got an iron deficiency situation going on, that is a plant immobile nutrient. In other words, the deficiency symptoms show up first at the top of the plant and last at the bottom of the plant. So if you sample at the top of the plant and last at the bottom of the plant, so if you sample at the top of the plant you're going to have less iron in that plant tissue than if you're sampling at the bottom. So you need to know at what crop stage you need to be sampling what part of the plant, because we do have a standard set of plant tissue analysis methods and they are calibrated to be working with specific plant parts at specific crop stages.

Jodi:

And this is kind of a nerdy aside speaking of iron tissue testing, when you're sampling, like, say, if you ever wanted a tissue sample for iron deficiency, just keep in mind that there is a level of iron in all the soil right, and so if you ever get any sort of soil on those leaf tissues, that can affect the results.

Sarah:

It's a great point, Jodi, because when you select that plant tissue to be submitting for iron, you should really try to brush that soil off as much as you possibly can.

Sarah:

When I was in a research situation, we actually had protocols for actually washing that leaf tissue. Obviously, we don't have the luxury of carrying around a five-gallon bucket with us through a half section, so that's always an interesting situation, right? It's really important to make sure that you get as much soil off of that as possible, and I think it goes to remind ourselves that tissue sampling it isn't necessarily indicative of an exact quantity of the nutrients that's in the plant. It is really an indication about whether you are dealing with nutrients in a sufficiency or a deficiency situation. You can't use plant tissue sample results to determine the amount of fertilizer that it takes to correct a nutrient deficiency in the field, but it can tell you if what you're looking at is in fact a nitrogen deficiency or a potassium deficiency or an iron deficiency. It'll help you narrow down what your problem is and from there you might need more information to help determine what you need for that corrective action.

Jodi:

Yeah, absolutely. It's so important to have a goal in mind of what you're doing with the tissue test. You're going to find out that the data that you get doesn't have a whole lot of value if you're just going out to the field and collecting a tissue sample. What are you doing with that tissue sample? Are you trying to evaluate whether or not you need to apply additional nutrients? Are you trying to diagnose a specific issue in one part of the field? It's really, really important to get specific on what you're trying to do. And so, with Sarah's example, right, like, if we're going to go out and figure out, if try to figure out if we're deficient in nitrogen, we might want to also, at the same time that we're collecting that good and bad tissue sample, to take a good and bad soil sample with that so that we can figure out. Okay, if I get back with a deficiency for nitrogen in this tissue in my bad sample, that soil test will tell me how much additional nitrogen I'm going to need.

Sarah:

Your tissue sample is going to tell you what the problem is and your soil sample is going to tell you what the corrective action is that you need. Furthermore, if you take that soil sample from the good area and the bad area, it's going to reinforce what your tissue sample results are.

Jodi:

So when you want to go out and take a plant tissue sample, remember to have a goal in mind. Look at the instructions on the bag, make sure you're collecting the correct part of the plant and then have an idea of what you want to do with those results once you get them back.

Sarah:

And if you are trying to troubleshoot an issue going on in the field, make sure that you're pulling samples from both the good area and the bad area.

Jodi:

All right, you should know now what three times seven is.

Sarah:

Don't ask your corn plant math problems. That's not going to solve any problems. Just take a good tissue sample.

Jodi:

Tune in next time for a tiny bite of knowledge from GK Technology, where we have a map and an app for that.