Bernardita Sallato describes methods to evaluate limiting factors related to plant nutrition in orchards. Recording from WSU virtual workshop Soil Health in Orchards with project support from the Washington State Tree Fruit Research Commission.
| Audio | Visual |
|---|---|
| Thank you, Tianna. She asked me for a very challenging task to talk about techniques to maintain adequate plant nutrition in 15 minutes. | Title slide. Presentation title: Techniques to Maintain Adequate Plant Nutrition. Author information: Bernardita Sallato, WSU Extension. |
| So what I wanted to do, and you’ve heard this concept a lot, is to think about the limiting factors. So I wanted to focus on the tree fruit industry in apples and cherries mostly, what the need, how the plants get these nutrients, and what factors can affect the uptake of these nutrients, especially in our region, in Eastern Washington. | Slide appears over background image of an orchard. Three bullet points are listed: What is needed, How to get it, and Factors. |
| So the most important, and I wanted to go through a priority list, so the most important factor that the trees need to uptake nutrients is actually light. Because the most important nutrients are carbon, hydrogen, and oxygen. And these nutrients account for 95% of the dry matter of the plant. So the most important condition factor for having a good nutrient uptake and nutrition in the plant is actually the sunlight, so we need good exposure, and of course, the water. With these two elements and the air, having the sunlight energy, we can create the photosynthetics and have a good supply for that main portion of the tree. | Slide appears over background image of an orchard containing the chemical formula for part of the photosynthetic process, a drawing of the sun, and a drawing of an irrigation line within the orchard. |
| But of course we want to focus in this talk on what we call the essential nutrients, the macronutrients, the ones that are demanded in higher quantities. These are nitrogen and potassium, that’s why I put them in bigger bubbles there. But we also need to think about other essential nutrients, we call them secondary macronutrients: calcium, sulfate, phosphorus, and magnesium. And there’s a lot of others that I am not adding here, but some that are very important especially for our region where we have alkaline soil, are the micronutrients: Boron, Zinc, Copper, Manganese, and Iron. Why I put this slide in the roots is because these nutrients are mostly uptaken by the roots of the tree. | Slide appears of a tree with exposed roots. Colorful bubbles containing the abbreviated element names appear around the roots of the tree as they are mentioned. |
| So to understand better, and to be able to manage better the nutrition, we need to understand that, because the pathway is through the roots and the root hair, roots are very important. You have heard a lot of talks, Andrew, David, and Tom, we all have talked about the importance of having good healthy root hairs, because that’s the pathway of nutrients. Now, there are differences between nutrients. Most of them go through mass flow, that means they go with the flow of water. So nitrogen, magnesium, sulfate, copper, manganese, boron, molybdenum, they all go with the water flow that gets into the plant. That means that we need to have uptake of water. So moisture and transpiration are also very important factors to be able to have these nutrients in the plant. Other nutrients that are macro and in very high demand are potassium and also phosphorus. Those two are moving into the root zone through diffusion, and this I drew it as a circle of high concentration around the roots. Its from higher concentration to lower concentration. So the roots are always uptaking these nutrients and reducing that concentration around the root zone. So there’s some movement there, again the diffusion also needs moisture in the soil. And there are other elements like zinc and iron that they move in both ways: mass flow and diffusion. | Slide titled “Nutrient Uptake” appears. The main graphic is a close up drawing of a root, with the root hairs and root tip labeled. There are areas of water around the root with red dots to indicate the elements that are taken up by mass flow. There are areas of soil around the root with multicolored dots to indicated that the elements are contained within the soil. There are also three circles of different colors contained within each other. The outer circle is touching the root hairs and contains the least elemental dots, indicating that the root uptake of nutrients creates and area of low concentration. Middle circle is further from the roots and has a higher concentration of dots, and the inner circle, which is furthest from the roots contains the highest concentration of dots. On the right side of this drawing there is a chart titled “Main Pathways” which states whether the mentioned nutrients are uptaken via mass flow, diffusion, or both. |
| This is a range of adequate levels, I’m not gonna stay in this table very long. I just want to show that we have this range of adequate levels in our tree fruit webpage. And if you try to maintain the soil within this range, you are probably very good in terms of the chemistry for nutrient management. | Slide titled “Soil analyses” appears, it is a chart with three columns: Soil, Range, and Method. It indicates the ideal levels of several of the mentioned elements for plant growth, as well as the supplemental nutrients used to maintain them. |
| Now I’m going to start focusing on those factors that are very important in our soils in Eastern Washington. So one of them is the soil pH, and soil pH can affect the root uptake of the nutrients in two ways. One is because the roots do like for pH… they are more comfortable within a pH of 5.5 to 6 or 7, but also because the nutrient availability changes in different types of pH. So you can see here that most of the nutrients are available within that range of 6 to about 8, most of the nutrients are available. | Slide titled “Soil pH” appears. It contains a chart of nutrient availability based on pH. There is a pH scale ranging from 4 to 10 along the top of the chart, and each element is represented by a horizontal bar with a color gradient that gets darker to indicated higher availability at a certain pH. There is a red box around the pH range of 6 to 8. All elements have moderate to high availability in this pH range. |
| Now, in our soils in Eastern Washington, where we have our larger production area. A lot of our soils are within the range that I’m showing now, the 7.5 to 9. You can see here, that especially phosphorus can be very deficient with high pH or not available, the same way with all the metals. The metals like iron, manganese, boron, copper, and zinc, they reduce their availability. So under these conditions, the most important practice that you should be trying to do is to manage the pH. | Slide remains the same but the red box shifts to contain the 7.5 to 9 pH range. In this range, the phosphorus along with the metal and metalloid elements have lower availability. |
| This is an example of the effect of high pH in soil, this is iron chlorosis in cherries. And its this very characteristic yellowing and chlorosis in leaves. | Slide titled “Iron Chlorosis (Fe)” appears with a photo of a small cherry tree with significant yellowing of the leaves. |
| And this is a very similar symptomatology in apples. One thing that is very unique to iron chlorosis is that the symptoms of the plant are the best indicator of that deficiency. And because iron is affected most dramatically with the change of pH, sometimes it covers the deficiency of other metals like manganese, copper, and zinc. So if you have iron chlorosis in your orchard, or in your plant, you most likely have high pH and you have to manage the pH before you want to manage the nutrition of those elements. | Photo appears on the slide of a zoomed in photo of apple leaves that show significant yellowing. |
| These are other examples of consequences of high pH in soils. I’m going to show one here that is important especially when we don’t put phosphorus in our soils at planting we have this brownish border in the leaf that is related to phosphorus. And I’m gonna leave the other two maybe for questions because that’s a whole new story. | Slide appears with three photos, the first is an apple with brown pitted spots on it’s skin, the second is a pear with brown spots in it’s flesh, and the third is a plant with dark brown coloration on the outside of the leaves. The mouse moves to point to the browning of the leaves in the third image. |
| In Washington, what has led to high pH, in most cases its because we call the caliche. It’s a layer of calcium carbonate, that, when it’s in contact with water, you can see here the chemical reaction, it releases OH. | Slide titled “Caliche = high pH” appears. It contains a photo of the calcium carbonate, seen as white mineral deposits in the soil, as well as a graphical representation of calcium carbonate in soil reacting with water. To the side there is a chemical formula of calcium carbonate reacting with carbon dioxide and water to produce carbonic acid and OH. These products are then shown in a chemical formula to react with Calcium |
| And so that increases the pH of the environment. And that increase in pH, is due to the parental material, which is the mineral of the soil. The problem is that it’s hard to manage, so you have to live with it. The buffer capacity means that you can reduce the pH by different management practices, but it will always go back to the normal, high levels of pH. So it’s a lifetime effort. | An arrow and a bullet point list appears under the chemical formula of carbonic acid and OH reacting with calcium. The bullet points state that this chemical reaction increases pH and has high buffer capacity. |
| Now, besides reducing the nutrient availability, the calcium carbonate in some areas can also be a physical impediment, because it creates a layer that reduces the possibility for roots to go and penetrate. So they normally stay in the upper layer of the soil, but also it reduces the water movement through the soil, so its a layer and a physical impediment of movement of water. And because this layer is very variable in the orchard in depth, the variability of this layer can create a high variability of growth and impediments throughout the orchard. | A slide titled “Soil limitations” appears. It contains an image of tree roots which are unable to penetrate the calcium carbonate layer of the soil. The calcium carbonate layer is seen as white mineral deposits in the soil, and the roots are shown to be growing above this layer. Three bullet points appear next to the photo stating that the caliche causes reduced nutrient availability, physical impediment, and reduced water movement. |
| So with that, I want to go back to the idea that we need to maintain healthy roots because those are the first and most important ways that the nutrients will be taken up. So if we think about the limiting factors that we mentioned before, you know, light exposure, we need water, and of course we have healthy roots. | Slide titled “Healthy Roots” appears. It contains a small image of an apple with the label “Fruit”, a small image of an apple tree with the label “Shoots”, a large up close image of tree roots with the label “Roots”, and a medium sized drawing of nutrients transferring from the soil to the root tips with the label “soil”. |
| Now because healthy roots can be affected by many factors, I’m gonna go back to this physical barrier. And I want to show this one because it’s been very common at least in the Yakima Valley, that sometimes we don’t have the calcium carbonate layer, but we do have a layer of compacted clay. And this is very common in the soils in Washington with different formation, and where we have different layers of texture soil. So in this case we have a layer of more clay type of soil that is more compacted so the roots grow only in the surface of that soil and you have less area for growth. | Slide appears containing a drawing of a tree and it’s root system below the soil and an image of tree roots. In the image, there is a lighter colored layer of compacted clay within the soil. The roots in the image do not grow into this layer, and remain close to the surface. |
| But there are other limiting factors. So just to think about in your soil, again like I mentioned before in the video, doing a profile a bit in your ground will sometimes help you to identify right away what could be the limiting factor before you have to do any other type of analysis. Because these are one big priority, if you don’t have roots, you wont have apples. | Images appear on screen of a hole filled with water, a white mineral on the surface of the ground, and of an orchard that is covered in ice. |
| Now I’m gonna go to the topic of nutrition in the soil. | The slide titled “Healthy Roots” appears again, but the image titled “soil” is enlarged to indicated that it is the focus of this section. |
| And I’m gonna only focus, because of the short time, I’m only gonna focus on those that I think are very important for Washington tree fruit growing. This is a prospection that I did for a project with the USDA, and we evaluated all the nutrient analysis and physical properties of soil. And here I want to show that, for example, calcium, that is one element that growers put a lot on a weekly basis throughout the season because of the bitter pit problem and calcium related disorders. Only three soils were low in calcium availability. This is the line that we consider an adequate range. The rest of the soils were within the adequate range and even in the very high range of calcium availability. | A slide titled “Soil Ca in WA” appears containing a bar graph of calcium availability in 80 different soil samples. The y-axis is labeled Ca (meq/100g) and ranges from 0 to 30. A yellow line runs horizontally at 5 on the y-axis indicating the ideal level for calcium availability. Only 3 of the tested soil samples fall below this line with most samples being far above this line in terms of available calcium. |
| Now when we plot the calcium levels in the soil with the potassium levels in the soil, another cation, that’s where we see most of the problems; because I have never seen values this high in my life and I have done a lot of soil samples, especially back in Chile where I come from. Anyway so here is the 200 parts per million which is recommended for tree fruit growing. You can see that when we have low values of calcium available, we also have low values of potassium available. And these soils are sandy soils in Mattawa, and it’s really common in a sandy soil where you have both in limiting quantities. But that’s very easy to manage, I think. What is more challenging is when you have adequate levels of calcium in the soil, especially in the mid range, but you have these levels of 700 parts per million, 800 parts per million, because then you have a big imbalance of cations in your soil. | Another graph is overlayed on the previous graph. The new graph is of potassium availability. The y-axis is labelled “K mg/kg” and ranges from 0 to 800. A white line runs horizontally at 200 on the y-axis indicating the ideal level for potassium availability. The potassium levels are low for the same three soil samples, and many of the soil samples have potassium very high above the ideal range despite the calcium levels being adequate for those samples. |
| And we know that when we have a cation imbalance we might have difficulties for uptake. Here is a chart that shows with ammonium, ammonium also has a charge, and when we have too much ammonium in the soil, we have a very big decline in potassium when that ammonium increases. So it reduces the availability of potassium. | A slide titled “Balance” appears containing a line graph plotting the decline in potassium as more ammonium is introduced into the soil. |
| This is also one very well known in this region, when we have high levels of potassium, we can affect the uptake of calcium and magnesium. The upper line is magnesium, and it declines when we increase potassium. And the lower line is the decline of calcium availability. So within these nutrients, there’s also differences in the impact of availability for these different nutrients. So calcium is really impacted by high levels of potassium, and you can see here in the range of 200, it really reduces calcium availability. | Another line graph appears on screen plotting the decline in both leaf calcium and leaf magnesium as the potassium levels is increased. The decline in calcium is much sharper than the decline in magnesium. |
| Okay, so I’m not sure how I’m doing with time, but I want to talk about something a little bit more practical about the “When?”. When we need to then start thinking about these nutrients, and I’m gonna focus on the most complex one. | Slide titled “When?” appears with a background of a blooming orchard. |
| Well, before that, I’m gonna talk about the conditions in the spring. Why is the spring so important? Because we’ve been measuring, and this has also been confirmed with that work by Denise Nielson and others, that root growth starts requiring moisture at developmental states, but also requires temperature in the soil. And what we have seen is that, in apples and in cherries, the temperature required for root growth is about 59 Fahrenheit, which is around 15 degrees Celsius, to start growing. And in some cases we might have two peaks of growth. And those timings are when the roots are uptaking most of the nutrients. | Slide titled “Root growth” appears with a line graph of tree growth. The x-axis is dates from April 1st to October 21st, and the y-axis is temperature in Fahrenheit from 0 to 80. There are two arrows indicating growth peaks at 59 degrees and 70 degrees. There is also an image of tree roots in an orchard shaded by a wooden board which is propped up by a smaller piece of wood. |
| This is work done by Denise Nielsen, and it also shows, not only when the roots are growing, but also shows the use of nitrogen by the plants in different states. And the most important part here that I want to highlight is that the first state of growth, and this is also for cherries, in other words, everything relies on the reserves that are in the roots, the healthy roots, from the previous year. And around 40 to 60 days after full bloom is when you actually start using the nitrogen that is in the same season, the uptake of nitrogen from the same season. Keep this in mind for what I’m going to be speaking about later, but everything needs to be analyzed in combination to be able to make a good management decision. | Slide appears containing a line graph of nitrogen usage by shoots, spur leaves, and fruit. The y-axis is labelled “N (g/tree)” and the x-axis is labelled “Day of the year”. There is a vertical line at 140 days that indicates when the tree stored nitrogen moves into spur leaves, shoots, and fruit as well as arrows pointing to bud break, full bloom, petal fall, and end of cell division on the x-axis. |
| So this is a very busy slide, I don’t like very busy slides, but it’s important just to show the complexity of nitrogen, and this is the cycle of nitrogen. What I want to show here is that whatever we put in the soil, either manure, compost, or fertilizer, will mineralize. It will take some time depending on the source and the condition of the soil, but it will end up in the form of ammonium and nitrate. Both forms are the forms that the plants can uptake, they are available forms of nitrogen for the plant to uptake. Now ammonium, because it has a charge, can be absorbed to the clay particles of the soil. So that’s a good thing for ammonium in terms that we don’t lose it right away because it can be absorbed into the clay particles. But if we put ammonium under very hot condition and dry condition, we can lose that ammonium in the volatilization process. So that’s the good part, the absorption, that it stays longer in the soil, but also it can volatilize. In very high pH, in pH above 8.5, it can also be lost by volatilization. | A diagram appears illustrating the nitrogen cycle in the soil, including plant uptake, soil nitrogen forms, and transformations of the nitrogen into different forms. |
| Now ammonium eventually will become nitrate in the soil. And nitrate, the problem that we have is that it doesn’t have a positive charge so it doesn’t stay in the clay particles and it can be leached. If we don’t also have oxygen in our soil, if we irrigate too much and we have lack of oxygen, the microorganism need to nitrify the nitrogen. So we can also lose it by denitrification. The main point here is that there’s many losses in the nitrogen application. So, let’s think about the states of root growth in the spring. The requirement of the plant to uptake nitrogen especially in the spring 40 to 60 days after full bloom. So then, when do we need to apply nitrogen? It’s during that period of root growth. If you apply nitrogen before, in the cold soils, or during the winter, or even in the fall, you’re most likely gonna lose that nitrogen. So it’s not a very efficient way to manage nitrogen in the soil. | An additional graphic is added to the diagram demonstrating ammonium becoming nitrate and leaching from the soil. |
| And to finish up with this, I’m not sure, I think I don’t have any more time. But just to finish this, as a contrast, phosphorus is completely the opposite. We don’t lose phosphorus in the soil by these other ways that we lose nitrogen so it stays in the soil. So the timing for phosphorus could be any time of the year, whenever you feel it is more practical for your orchard to apply the phosphorus. The downside of that is that it doesn’t move very much so it’s hard to reach to deeper zones if our roots are growing deeper in the soil. It’s a little bit more of a challenge | A diagram appears illustrating phosphorus cycling in soil, showing plant uptake, soil phosphorus forms, and processes that limit availability. In contrast to the nitrogen cycle diagram, there are far fewer processes in which the phosphorus is lost. |
| So with that, I’m gonna leave you with this phrase from my colleague, Andrew McGuire here in the meeting, that I think is fundamental. For me it’s very hard to give one recommendation for everybody, because I think it has to be done block by block. So the biggest question is, go and try to identify what is that problem in your soil, to be able to manage that nutrition. | Slide appears with background of a zoomed in picture of tree roots. Text on slide reads “Soil (health) evaluation begins by asking “What’s the problem with my soil?”. |
| With that, I’m finished and open for questions | Slide appears with information on the 2020 Soil Health in Orchards Workshop. |
