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Mike Howell (00:08):
The Dirt, with me, Mike Howell, an eKonomics podcast where I present the down and dirty agronomic science to help grow crops and bottom lines. Inspired by eKonomics.com, farming’s go-to informational resource, I’m here to break down the latest crop nutrition research use and issues helping farmers make better business decisions through actionable insights. Let’s dig in.
(00:38)
Well, hello again, everyone. Welcome back to The Dirt. We have with us today Dr. Jeff Schoenau with the University of Saskatchewan. Jeff’s, good to have you with us this morning.
Dr. Jeff Schoenau (00:47):
Hey, it’s great to be here, Mike. Happy to be on the podcast.
Mike Howell (00:51):
Jeff, if you would give us a little bit of background about yourself. Tell us where you are and what you do.
Dr. Jeff Schoenau (00:55):
Sure thing. I’m a professor and I hold the Saskatchewan Ministry of Agriculture Chair in Soil Nutrient Management and I’m at the University of Saskatchewan in Saskatoon, Saskatchewan, which is a province in the center of Canada. I’ve been there since 1989. I finished my PhD in 1988, so I’ve been there since doing research teaching and extension work on soil fertility and fertilizers, soil management, soil nutrient cycling, and I also farm with my spouse Lynn on a 1600 acre grain farm in south central Saskatchewan. That grain farm also serves as a location for a lot of the research work that myself and my graduate students do.
Mike Howell (01:33):
That’s pretty convenient. Jeff, if you would, tell us a little bit about the crops that you grow in your area. I know things are a little different in Western Canada than they are here in the southeast United States, probably don’t have very much cotton up in that area.
Dr. Jeff Schoenau (01:46):
Nope, not too much cotton at all, but we grow quite a diverse array of crops. A very common rotation that’s used here would be a cereal grain legume oil seed rotation, so something like a wheat P canola rotation would be very common, three year rotation, four year rotation, sometimes with some other cereals put in there like flax or barley, some other pulse or grain legume crops like lentils are in there as well. So small grains. We don’t grow a lot of corn here in Saskatchewan, but there is some. There also are some soybeans as well, but those crops tend to be more common moving towards the southeast into Manitoba and then of course, as you’re well aware, into the US Midwest there, south of Manitoba into North Dakota and Minnesota.
Mike Howell (02:32):
Okay. Thanks, Jeff, for that background and a little bit of what’s going on in Canada this morning. If you’re ready, let’s go ahead and dig in. Let’s get to the dirt and today we’re going to be talking about zinc. First off, what is the function of zinc within a plant?
Dr. Jeff Schoenau (02:45):
Well, I guess we always need to remember that the zinc is an essential element. It’s a micronutrient, so it’s required in relatively small amounts, Mike. Typical zinc concentrations in plants might range from 20 to a hundred ppm, so not a lot there, but nonetheless, it’s an essential element. It has to be there for the crop to grow, develop, reproduce, produce seed. What does zinc do in the plant? Zinc’s, very important in photosynthesis. It plays a lot of roles in the plant as well. Things like enzyme function activation, which is really important in lots of processes in the plant like protein production and photosynthesis obviously.
(03:21)
Also zinc’s a regulator of hormones in the plant and hormones play a lot of important functions in the plant in how it grows and develops. Without zinc certainly or zinc deficient conditions, yield definitely suffers. And interestingly, zinc also plays an important role in the viability of seeds. It’s very important in germination. It plays a lot of functions. In zinc deficiency, often we see in the leaves, smaller leaves and that’s why we sometimes refer to zinc deficiency as little leaf disease and sometimes also produces some chlorosis or yellowing in between the veins. It’s a very important micronutrient element in plant nutrition.
Mike Howell (04:00):
Okay. Jeff, thanks a lot. Probably 30 years ago here in the deep south, we were predominantly cotton producers. Mississippi had 1.2 million acres of cotton at one time and for various reasons we made a shift at that time away from cotton and grow a lot more grain crops now, predominantly corn. And when we made that switch, we started seeing zinc deficiencies show up a lot more often. Do some crops need more zinc or do they just show that deficiency symptoms more?
Dr. Jeff Schoenau (04:26):
That’s a very good example there, and corn is a high zinc user and also up here in the Great Plains in western Canada, we also find that legumes in particular, are grain yield legumes that we grow like peas and zinc and beans are also high zinc users as well. In cereals, zinc is very, very important for the production of those crops as well. I guess when it comes to zinc deficiency and issues of deficiency, up here, widespread zinc deficiency is not common, but it does show up in certain areas, in certain locations even within the field, so we tend to see zinc deficiencies sometimes localized within fields.
(05:03)
And oftentimes, Mike, they’re associated with specific soil conditions. So where we find zinc deficiencies to arise, and I think we can say this in a general sense, would be soils that are high pH that are oftentimes calcareous, meaning that they contain a high content of calcium carbonate or lime. Also, a sandy texture tends to contribute to zinc deficiency because the minerals that supply zinc are oftentimes found in the clay sized fraction rather than the sand sized fraction. And of course, anytime you’re pulling off big yields year after year, especially with crops that are high zinc users, taking that off the field, that can also contribute to zinc deficiency as well.
Mike Howell (05:41):
Jeff, you mentioned soil pH and our listeners are going to start thinking, I prompt all of our speakers to talk about soil pH because every guest I’ve had on has mentioned soil pH at some time, but I promise we didn’t talk about this beforehand, but the relationship between all of these nutrients and soil pH is so critical. And, listeners, if you’ve missed some of these previous episodes, I encourage you to go back and listen to the episodes we did about soil pH and making sure that pH is in the correct range for what crops you’re growing.
(06:07)
Jeff, let’s move on a little bit. What form of zinc is going to be available to plants? Most of these nutrients can take on different forms. What’s going to be the best for plants to be able to take up?
Dr. Jeff Schoenau (06:18):
Micronutrient chemistry in the soil is always interesting and that applies to zinc as well. Total concentrations of zinc, that’s the total amount typically around that maybe 40 to 60 part per million range and about five to 10% of that total zinc is actually what we would call plant available, Mike. And we can measure that with a soil test. We can measure the concentration of it using some type of an extraction. We can measure a supply rate using a ion exchange resin membrane probe here in Canada. In Saskatchewan, we use, we call it the PS probe, and really what the plant available form is chemically is a KAT iron zinc Zn with two positive charges and also chelated forms of zinc in the soil are important.
(06:59)
We’re talking about a chelated form of zinc, is that zinc like other micronutrient metals, namely copper and iron, tend to be reactive in the soil with soluble organic matter. And what happens is the zinc reacts with soluble organic matter there present in the soil and forms this complex or chelate that keeps that zinc soluble and enables it to move in the soil to where the root is and be taken up. The interaction that zinc has with organic matter in the formation of these chelates is really important in its availability and that also comes through as well into micronutrient fertilizers because some of the micronutrient fertilizers that are available are also sold in chelated form.
Mike Howell (07:38):
Okay, great information. Jeff, you kind of touched on zinc being mobile within the soil and how it moves in that soil solution. What about when it gets in the plant? Is it considered mobile within the plant or did it kind of stay in one place?
Dr. Jeff Schoenau (07:50):
I would say it’s not highly mobile in the plant, Mike. It moves in the phloem, and so that poses sometimes a little bit of challenge for the plant to mobilize zinc from the vegetative portions into the seed of the plant. And even in the soil, I think, we would consider zinc to not be highly mobile because it’s very reactive in the soil. The zinc KAT iron will readily react with the soil constituents. It’ll react with oxides and become sob or precipitated. Zinc will react with carbonate minerals very readily and form zinc carbonates, which are insoluble, which can’t move, which limits the bioavailability of that zinc, Mike. Generally, I would say zinc’s not a highly mobile element, and for that reason, placement of zinc can be important in terms of fertilizer management.
Mike Howell (08:34):
That’s right. Jeff, you just mentioned that zinc can interact with the carbon. What about other nutrients in the soil? Don’t we have some reactions with calcium and some other things that can tie that zinc up as well?
Dr. Jeff Schoenau (08:44):
Indeed, indeed. As I said, zinc can react with oxides and forms zinc oxide. Precipitates can react with carbonates to form zinc carbonate minerals that are insoluble. Also, we need to be aware of the importance of balance of zinc with other nutrient elements, including micronutrients and macronutrients like phosphorus. And I guess, when it comes to zinc, maybe one of the first thing this comes to mind when we talk about nutrient balances is that zinc is the potential for phosphorus induced zinc deficiency. And I think probably a lot of folks out there have heard of that. And really what we’re talking about there is we’re talking about if you add a large amount of phosphorus to a soil that is maybe marginally zinc deficient to begin with, the addition of that large amount of phosphorus can induce a rather severe zinc deficiency and cause some rather severe yield reductions associated with that.
(09:36)
And the exact nature of that, Mike, is not very well known, and we’ve actually taken a look at that in some of our research. Originally, it was thought that maybe what’s happening is the phosphorus is reacting with the zinc in the soil and causing it to precipitate out, and so plant can’t take it up. That doesn’t really seem to be the case and it maybe seems to be a little bit more physiological in that high amount of phosphorus actually interferes with uptake and redistribution of zinc within the plant, meaning it stays behind in the roots when you got lots of phosphorus. And some even suggest that maybe that high amount of phosphorus is reducing the amount or the infection of the roots by this beneficial AM fungi that allows it to also access a zinc in the soil as well. So yeah, the mechanisms aren’t really clear on this, but it’s certainly something to be aware of.
(10:19)
One of the other things that we’ve observed as well in some of our recent research, Mike, related to zinc interactions in the soil is it can go the other way as well in that if you add a large amounts of copper and zinc fertilizer to the soil without adding any phosphorus, you can also induce a negative effect and reduce the uptake of phosphorus and the yield of that crop. Bottom line balance is really important for zinc as well as other nutrients. We want to have that appropriate balance so we don’t end up with these negative interactions.
Mike Howell (10:51):
Great information, and that’s something we always talk about is this nutrient balance and making sure we’ve got what the plant needs of each one of these nutrients in the right proportion in that soil. Jeff, if a grower was to determine that he did have a zinc deficiency or his soil test report came back showing that he needed to add some zinc, what are some fertilizer sources that he could use to make sure he gets that zinc in the soil?
Dr. Jeff Schoenau (11:12):
Yeah, there’s a variety of fertilizer zinc sources that are available. One of the most common is a sulphate salt, zinc sulphate, and that’s a widely used zinc fertilizer. There are also other forms of inorganic zinc. Zinc oxides are another source. The zinc oxides tend to be less soluble and less plant available in the short term than the sulphate salts. And then the third category is the chelated forms of zinc. And those chelated forms of zinc tend to be more expensive, but they also tend to be more efficient and as a result, recommended application rates are lower for those chelated forms than they are for the salt of zinc.
(11:48)
I think it’s interesting as well, when we think about method of application of that zinc fertilizer, oftentimes the zinc sulphate forms are soil applied, and what we find is when they’re soil applied at higher rates, let’s say five pounds of zinc sulphate per acre applied in our small grains production system here in western Canada, those soil applied sulphate salts at higher rates can carry over into the following season, meaning that what the crop didn’t use that year, you can get some carryover and benefit to following crops. For the chelated forms because they tend to be applied at lower rates, there is less carryover into the following years.
(12:24)
The other thing I want to touch a little bit on when it comes to fertilizations, Mike, is soil application versus foliar application. And we have found as others in our research work that both soil and foliar applications of zinc can work well. Typically though, those foliar applications are made at a lower rate, especially if they’re a chelated form. So because of that, you don’t see much residual effect or benefit carrying over into the second season. But the higher applications of the soil applied zinc, like a zinc sulphate salt, we do see that carry over effect into a subsequent season or even the season beyond. And that can be important for growers who are looking at replacing what they’re taking out in crop removal and want to maintain their fertility over the long term, Mike.
Mike Howell (13:07):
Perfect. And that could also play a difference in what the grower determines to do is if he’s got rented land or if he owns his land, and has a long-term lease on that, so don’t want to use those expensive products if this may be the last year he’s got that piece of land. So great information.
Dr. Jeff Schoenau (13:21):
Exactly. It just depends kind of on your philosophy and it is possible to do soil building with zinc. And actually some of our research work that we’ve been doing very recently, Mike, has been looking at these eroded knolls. Those are locations in our landscape here in Western Canada that we can particularly identify as oftentimes zinc deficient, potentially responsive to zinc fertilizations. And it fits in nicely with the whole concept of precision fertilization only put that zinc in the areas of the field that need it. We’re looking at how we can build up the zinc fertility of those knolls by applying a zinc fertilizer specifically to those areas. And we are seeing some benefit from it in terms of some yield responses, particularly in our pulse crops like peas.
Mike Howell (14:03):
Okay. Jeff, you’ve mentioned several times your graduate students and your personal farm doing a lot of research, and you’ve mentioned several research trials that you’ve talked about through the course of this podcast. Is there any other pertinent research that you’ve been working on, something our listeners may want to hear more about?
Dr. Jeff Schoenau (14:17):
I guess there’s one thing I would mention a little bit, and that is we think about response to fertilizers not only in yield but also in crop quality. And I think it’s important to say in the case of zinc that in fact the zinc content of grain is very important consideration in human nutrition, Mike. About 30% of the world’s population don’t have enough zinc in their diet. It’s very desirable then to have concentrations of zinc in that grain that they’re consumed in order to meet those dietary requirements. And what’s commonly looked at in grain as an indicator of human bioavailability of zinc is what’s called the phytate zinc ratio. And we look at this ratio phytate zinc ratio because phytate is actually an anti-nutritional and binds zinc up and prevents the human intestine from absorbing it. So we’ve looked at how zinc fertilizations strategies affect this phytate zinc ratio in pulse crops like lentil because lentils that we produce in western Canada are sold to a large extent in the Middle East and in that part of the world, a zinc deficiency is fairly common in the human population.
(15:19)
And so we’re interested. How can we fortify this zinc in the grains that we’re selling to the population in these regions of the world? What we found is that to a certain extent, fertilizations with zinc, and we found particularly foliar applications of chelated zinc were effective in reducing this phytate zinc ratio and increasing the human bioavailability of that zinc. And although our growers don’t get directly paid for that, I mean, doing something that can improve the human nutritional value obviously has appeal when it comes to the marketability of any crop, Mike. So we think about a micronutrient like zinc, not only in terms of its effect on yield, but also its effect on quality. And that translates as well, not just to grain legumes, pulse crops, but also to cereal crops as well.
Mike Howell (16:01):
Great information, Jeff. Yet this world population is continuing to increase. We’re not getting any more farmland produced, so we’ve got to be more productive and we’ve also got to make sure we’ve got all these nutrients in this food that we’re producing to supply the world.
Dr. Jeff Schoenau (16:14):
Indeed.
Mike Howell (16:14):
Jeff, we’ve covered a lot this morning about zinc and zinc nutrition in the plant. Is there anything else we need to touch on this morning?
Dr. Jeff Schoenau (16:21):
I’ve worked for many years with a lot of different plant nutrients in research and looking at the chemistries, their fate cycling, as well as the more practical aspects of plant response, and micronutrients like zinc I’ve always found to be rather challenging in research work because of the variability that we see inherently in the response to a micronutrient. And I sometimes refer to micronutrients as being kind of ghostly, for lack of a better word, and that is the deficiency, the symptoms will appear and then suddenly they’ll disappear. And why is that? Sometimes not really very easily understood or easy to predict. And so seen in our research work soils that test very low and you expect to see a response to the micronutrient tradition, but you don’t. And on the other hand is soil that will test rather high and you don’t expect to see a response, but you do.
(17:07)
And oftentimes it’s just a consequence of environmental conditions, how things like soil temperature and moisture interact with the plant, its rooting system and all of those complex variables interplay to ultimately affect how much zinc that plant sees and the response to the added fertilizer. And it’s not easy to predict. It’s just kind of the nature of the beast. When it comes to making a micronutrient fertilizer recommendations like recommendations for zinc, we always have to be aware that it’s rather hard to conclusively predict whether there’ll be a response or not. And so that needs to be taken into consideration in terms of what the grower expects to see, and they may not see a response that year. But I guess the thing about a plant nutrient like zinc is that it will hang around in the soil, it’ll stay there. If it wasn’t used that year, it’ll carry over and be there for a subsequent year. It’s not easily lost from the soil system. So those are some of the considerations, I think, when we’ve been talking a little bit, Mike, about short term versus long-term plant nutrition planning.
Mike Howell (18:05):
So kind of like an insurance policy, you can kind of build it up and make sure you’ve got enough to cover yourself this year, and if you keep building up maybe one year you can skip that application a few years down the road.
Dr. Jeff Schoenau (18:15):
Indeed. Especially for the folks that are out there and they’re shooting for the top end of that yield curve and they want to make sure that there’s no possible limitation. Those are the folks that are probably most interested in that micronutrient application aspect of their fertility plan.
Mike Howell (18:29):
Jeff, we sure appreciate you joining us today. We’ve covered a lot of valuable information that the growers listening to this podcast will be able to benefit from. Thanks again. I know you got up awful early this morning to record this podcast, and we surely appreciate your time this morning.
Dr. Jeff Schoenau (18:43):
Hey, no, it’s been great there to be with you, Mike, and to share some thoughts with the folks out there.
Mike Howell (18:50):
Listeners, thanks for joining in today. We hope you’ve learned a lot about zinc and how to manage zinc in your fields. We want to remind everyone to please pass a link to this episode along to your friends and neighbors so they can enjoy the podcast as much as you are. Also, I want to remind everyone to tune in again next week when we’ll be visiting with Eric Snodgrass. Now, you probably remember Eric from previous episodes. Eric is with Nutrient Ag Solutions and he’ll talk about the weather forecast and tell us what we can expect as far as weather in this upcoming harvest season. Until next time, this has been Mike Howell with The Dirt.
