3.5 Tiny Bytes: Understanding Plant Nutrient Mobility

Awareness of nutrient mobility in plants drastically improves in-field diagnosis of crop issues. In this episode, we dive deep into plant nutrient mobility and how nutrient mobility impacts visual symptoms in the field.

• Discussion on the concept of nutrient mobility 
• Insights into mobile vs. immobile nutrient deficiencies 
• Importance of tissue testing for accurate diagnoses 

Relatively immobile nutrients (symptoms will appear on newest leaf tissue): S, Zn, Fe, Cu, B, Ca, Mn, Mo, Ni

Relatively mobile nutrients (symptoms will appear on oldest leaf tissue): N, P, K, Mg

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Cover art diagram courtesy of the 4R Plant Nutrition Manual, IPNI 2012 (https://www.canr.msu.edu/news/identifying_nutrient_deficiency_symptoms_in_field_crops)

https://gktechinc.com/

Chapters

• 0:00 Tiny Bite of Knowledge
• 33:00 Nutrient Mobility Explained
• 8:05:00 Common Nutrient Deficiencies Recap

Transcript

Sarah: 0:00

And now it's time for a tiny bite of knowledge, Jodi. Why is my corn purple? I don't know. Sarah, Did you give enough fertilizer? I don't know. I've just never seen purple corn before.

Jodi: 0:24

Okay. So maybe if you've been around nutrient deficiencies for a while, you might think are we doing a podcast on phosphorus deficiency, which we typically associate with purple corn? But what we want to talk about today is the mobility of nutrients in plants and why we might see certain nutrient deficiencies on the upper or the young parts of plants or the lower parts of plants.

Sarah: 0:47

That's absolutely correct If we back up one second. My professor at NDSU, dr Goose, used to classify nutrients according to their soil mobility and their plant mobility. Today we're talking about plant mobility. Some nutrients move easier in plants than others and at the very outset most nutrients are mobile within the plant when they are not under any stress. However, once stress occurs or a nutrient is deficient, the plant automatically wants to send that nutrient to the younger tissues and the growing points at the top of the plant. That is its desire. It's going to try to preserve that area that's actively growing to the best of its ability. But some nutrients just don't move that easily in the plant, and so when you see a nutrient deficiency or discoloration of leaves on the upper or the lower part of the plant, that is explaining what type of nutrient it is and whether that nutrient is plant mobile or immobile in the plant.

Jodi: 1:53

Sarah, what are some of the nutrient deficiencies we typically expect to show up on the older part of the plant instead of the younger part of the plant? Or what are those nutrients that are more mobile in the plant versus non-mobile?

Sarah: 2:07

Yeah, it corrects Nutrients like nitrogen, phosphorus and potassium. Those are plant mobile nutrients. So when those deficiencies start to occur, what the plant is going to do is take those nutrients out of the bottom leaves and translocate those nutrients to the top of the plant where that younger tissue is growing, where that growing point is actively growing, so that the plant can really help keep that growth happening. So that's why when you see a phosphorus deficiency or a nitrogen deficiency or potassium deficiency, you're going to see those occurring on the bottom part of the plant first going to see those occurring on the bottom part of the plant first.

Jodi: 2:48

What nutrients might we expect to be plant immobile or appearing first in those new parts of the plant, versus the old Nutrients like iron?

Sarah: 2:54

zinc and sulfur, copper. Those are all nutrients that are plant and mobile and around, especially in the areas where iron chlorosis occurs. We see that frequently, that classic interveinal chlorosis of the upper leaves. Those nutrients they just can't easily move from the bottom tissues and translocate it up to that growing point so that younger tissue, that growing point, can be maintained and grow successfully. As a matter of fact, in some of the iron chlorosis work that I've seen locally there's actually been an effort to foliar feed iron into the plant with sprays. And what would happen when they would spray is that just where that spray would hit, the leaf would green up. However, they would block part of the leaf with a sticky note and the iron couldn't even translocate to the part of the leaf that didn't actually directly receive the application because it's just that immobile in the plant. So if you're trying to diagnose a nutrient deficiency in the field, first take a look at the plant and see where the discoloration or the affected leaves are occurring. Are they occurring on the upper part of the plant or the lower part of the plant?

Sarah: 4:11

Sulfur is also an interesting one. Sulfur actually looks an awful lot like nitrogen. However, it starts on the upper leaves and the upper tissues. But once it gets to be so sulfur deficient the whole plant starts to take to look yellow. And the way the pattern is for sulfur it's very similar to nitrogen, especially in wheat. Oftentimes a sulfur deficiency can get confused with a nitrogen deficiency in wheat because it goes from being those initial stages of that upper tissue turning yellow to the whole plant canopy turning yellow so quickly. So that's a place where if you put nitrogen out there and it doesn't green up, I would argue that most of the time if you see a yellow plant canopy in a small grain, it's probably nitrogen deficient. But if you put nitrogen on there to remedy it and it doesn't fix it, it was probably sulfur. Check it out.

Jodi: 5:05

And this is a really, really good place to plug tissue testing in terms of its ability to help diagnose some of these issues, or say if you're not as familiar with diagnosing these issues in a new crop or you're.

Jodi: 5:17

Or say if you're not as familiar with diagnosing these issues in a new crop or you're in a new place and not as familiar with what the practices are and what commonly occurs. Do take a diagnostic tissue test and what's important right is that you follow the instructions of whatever lab you're submitting that tissue test to and you're taking a test of both a plant that looks like it has that deficiency and collect it from an area where it does not look like they have a deficiency or that issue. That way, you can compare when you get the tissue test results back. Okay, what are my levels in the area of the field that I collected that looked like it had a deficiency versus where it wasn't? Because, yeah, I mean, some of these nutrient deficiencies can look pretty similar, and so having a tissue test is a really good way to diagnose that, get a cook result and help you apply only what you need.

Sarah: 6:03

Just like Jodi said, you need to take one from the area that's deficient and you need to take another sample from the area that is not displaying those symptoms so you can really compare those results, because it really will help you understand what that deficiency is. You need to be able to compare those sample results and, of course, the topic is mobile and immobile nutrients.

Jodi: 6:25

We haven't even touched on what some of these nutrient deficiencies can look like outside of nutrient deficiency. So taking a tissue test is a good way to hone in on what you're looking out and diagnosing what you got in the field.

Sarah: 6:37

It's pretty simple when you see something yellow, you see yellow corn to think right away that it's nitrogen. I have had farmers and agronomists confuse that with potassium and in my opinion I don't think those two things look at all the same, but they're yellowing of the leaves on the bottom, so I can see how that can get mistaken pretty easily. Also, note the misapplication of some herbicides can actually cause some purpling. So to verify whether it's phosphorus or not or something else, it's always a great idea to start with that phosphorus tissue test because it's a much cheaper test to run than an actual chemical analysis or pesticide analysis an actual chemical analysis or pesticide analysis.

Sarah: 7:22

Also, keep in mind that when you are taking that tissue sample, it's really important to take the right part of the plant that the instructions say to take for the stage of the crop that you are in. And that all comes back to the plant mobility. If you're at different stages in crop growth, those nutrients are going to be mobilized to different areas of the plant. So that's why you need to be making sure that you're at different stages in crop growth, those nutrients are going to be mobilized to different areas of the plant. So that's why you need to be making sure that you're sampling the correct part of the plant for the stage that that crop is in.

Jodi: 7:46

So, to wrap this all up again, when we're talking about plant mobile and plant immobile nutrients, when we're talking about plant mobile, these are nutrients that the plant can actually remobilize from a lower part of the plant and put up to the top of the plant, and so we're going to see these deficiencies in the old leaf tissue first. Those nutrients that are plant immobile are the ones that the plant can't remobilize and move someplace else. Sarah, do you want to give us a recap of what our common plant mobile nutrients are and what our common plant immobile nutrients?

Sarah: 8:17

are, Again, our plant mobile nutrients, for the most common nutrients that we're handling are nitrogen, phosphorus and potassium, and our most common nutrients that we handle that are immobile and you will see their deficiencies.

Jodi: 8:30

The immobile nutrients at the top of the plant sulfur, zinc, iron, copper, boron and, if you don't remember these, listen back to the podcast, do a quick Google search and that'll help you a ton when you're out there trying to diagnose nutrient deficiencies out in the field.

Sarah: 8:46

Absolutely, absolutely Purple corn.

Jodi: 8:50

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