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USDA NIFA | National Institute of Food and Agriculture
Soil Acidification in the Inland Pacific Northwest
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Episode transcription:
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Drew Lyon: Hello, welcome to the WSU Wheat Beat podcast. I’m your host, Drew Lyon, and I want to thank you for joining me as we explore the world of small grains production and research at Washington State University. In each episode, I speak with researchers from WSU and the USDA-ARS to provide you with insights into the latest research on wheat and barley production.
If you enjoy the WSU Wheat Beat podcast, do us a favor and subscribe on iTunes or your favorite podcast app and leave us a review so others can find the show too.
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Drew Lyon: My guests today are Emi Eleccion and Heidi Vandyk. Emi is a senior at WSU Pullman studying biological engineering and serves as a public relations chair for the WSU Biomedical Engineering Society Chapter. Emi has spent the summer investigating the potential of pennycress or stinkweed as a winter annual cover crop by researching the oil synthesis pathways of the plant. Emi’s project has focused on biochemical analysis of lipid content in pennycress leaves to ultimately engineer more efficient synthesis pathways to improve oil content in pennycress seeds.
Heidi is a junior studying biology at Western Washington University in Bellingham, Washington, where she serves as a leader for their Chi Alpha Campus Ministry chapter–I hope I got that Greek lettering correct. Heidi has also been working on this pennycress project, although her research focused more on root development of pennycress. Her project involved exposing developing pennycress seedlings to stressors, like growth hormones, and cold stress for incorporation of pennycress into Inland Pacific Northwest cropping systems.
Outside of their research, Heidi and Emi have been working with two other REEU participants, Nallely Leon and Skyler Allison, to research soil acidity.
So, the USDA-funded Research and Extension Experience for Undergraduates (REEU) program aims to expose students from WSU and other universities to different career paths in agriculture and provide them with skills for advancing their career path. Hello, Emi.
Emi Eleccion: Hi.
Drew Lyon: Hello, Heidi.
Heidi Vandyk: Hello.
Drew Lyon: So, doing research in pennycress, but also kind of investigating soil acidity and liming. Emi, can you tell me what lime is?
Emi Eleccion: Yeah, lime is a really versatile compound, which is calcium oxide. It’s derived from natural deposits of limestone or calcium carbonate, which is rocks formed millions of years ago as the result of shell, coral, algal, and other ocean debris accumulation. It’s used as an agricultural amendment but also in many other industrial processes like plastics, paints, paper, and more. And so, heat treating calcium carbonate or limestone is what reduces it to calcium oxide to lime.
And there are two types of lime. There’s calcitic lime which only contains calcium carbonate or calcium oxide or calcium hydroxide. And this is a liming material and all liming material is assigned a CCE score or a calcium carbonate equivalent, which signifies the neutralizing value that pure calcium carbonate would expect to alleviate soil pH per pound or per acre.
And there’s also dolomitic limes, which contains magnesium carbonate, which is good for soils, which is low in magnesium, which is an essential soil nutrient. And these can be slightly more efficient in neutralizing soil pH and may have CCE values greater than 100 so they can neutralize pH with lesser amounts of the same calcium oxide, but it would do the same effect.
Drew Lyon: Okay, so not all lime is the same is what you’re telling me. There’s different kinds of, different liming capabilities, would you say?
Emi Eleccion: Mm hmm.
Drew Lyon: Heidi, how does applying lime to soil reduce soil acidity or increase pH?
Heidi Vandyk: So, to fully understand what soil acidity is, we need to know what pH is. So, pH is a measure of concentration of potential hydrogen ions. The lower pH measures mean higher acidity and a greater concentration of exchangeable hydrogen ions. And on the flip side, a higher pH reading indicates a more basic and a lower concentration of exchangeable hydrogen.
So, the way that this applies to soil is that when we apply fertilizers, they are very acidic. And not only this, soil acidification also occurs through natural processes. So, when we apply lime, it’s a strong base. And in soils where pH readings are very low and highly acidic, when you add more base, it will raise that pH back up and neutralize the soil, which is important because plants aren’t able to grow and very acidic conditions. So, we need to make sure that that pH is in a mid-range place.
Drew Lyon: Okay. So, it basically removes hydrogen ions from the soil. So, the things that are making it acidic are these hydrogen ions and by putting lime on you remove those or take them out of the soil is that what’s happening there?
Heidi Vandyk: Well, essentially there’s another component to that. There’s a chemical reaction that happens. So, liming materials are oxides, hydroxides, carbonates–and these are all bases. So, the exchangeable hydrogen ions in the soil, they will react to a common liming material such as calcium carbonate and the reaction essentially causes the hydrogen to react with that and produce exchangeable calcium ions, water, and carbon dioxide. And yeah, so essentially what’s happening is the exchangeable hydrogen ions are being used up and converted to natural waste compounds. And the accumulation of the calcium ions in the soil, it will also, in effect, cause a modification in the thickness of the soil layer and will reduce the plasticity of the soil, which will improve soil workability, strength, and compressibility, and will reduce the swelling potential.
And in terms of timing, this will usually take a few days for calcium carbonate, but depending on what liming material you’re using like calcium illuminate, it may take longer. Usually that will take seven days.
Drew Lyon: Okay. Very thorough response to that question. I had never heard it stated that way, so I actually understand it better than I did before. Thanks.
Emi, there’s these different liming sources. So, what are the different methods of applying? I’ve seen a big rock lime and I’ve seen really fine powder. I assume they need to be applied differently. How is lime generally applied?
Emi Eleccion: Yeah, so there [are] a few different ways and I have a few that I can talk about, which definitely doesn’t cover all of them. But, the first would be surface application, which is just ideally an even coverage of the surface applying and if you have finer particles in your lime, ideally the spread width is between six to eight meters to get the fine particles to really equilibrate throughout the soil. However, this is really slow to address subsurface acidity because you’re only applying lime to the surface layer of soil, so that’s something to take account of if you are considering a surface application.
Another application is direct injection. This is kind of a newer current development and it places lime during deep ripping and so when it’s done successfully, subsurface acidity is quickly removed. And with proper distribution, there is yield responses of 20 to 30% in wheat, which is especially nice for places like the Palouse. And it’s especially good if compaction is a problem in your field. But there are also drawbacks of this. You obviously are going to need to spend a lot of money if you need to modify any of your machinery. And it’s also a very slow process of deep injection.
And then there’s also moldboard plowing, which happens when soil is being inverted. And so, the lime is being mixed at a greater depth with greater mixture of the topsoil and the subsurfaces, and this could still take some time for the lime to amend the now topsoil, which will create a barrier for root growth. Working the plow a little shallower at a higher speed may create this sort of angled lime to topsoil layer from the surface of the subsurface, which will provide a pathway for the roots to grow, which kind of alleviates that root barrier that you see with the mixing. And it’s proven really successful in sand plain soils with more mild surface acidity, so I would recommend using this with caution in higher acidic soils.
There’s also rotary spading, which is very effective for deep incorporation of lime up to depths of 30 to 35 centimeters. So, if you are growing crops with, you know, deeper roots, that’s a good option. Spades bury the topsoil while also lifting seams of subsoil to the surface. There isn’t exactly an even spread throughout the profile–there is a good distribution of lime though. So, through the cultivation depth with many areas of higher pH the lime mixed into the subsoil, it really lets the lime cover all your bases. And then this mixing improves contact of lime with acidic soil for rapid and effective neutralization, so higher rates of lime may be necessary as it’s being mixed in a greater volume of soil. And this is more recommended for when you’re incorporating lime to non-wetting soil because this is typically the best and sometimes the only realistic option to recover extremely acidic soil profiles to a reasonable pH.
Drew Lyon: Okay, so lots of different ways to get it on and incorporated depending on the circumstances you’re looking at, it sounds like.
Heidi, I’ve heard about people wanting to ask a question about can they apply sulfur to alleviate pH problems? Is that a possibility?
Heidi Vandyk: Yeah. So, liming with sulfur, that is a common thing that people will do. But it’s not to be confused with normal liming practices, because it will actually make your soil more acidic since sulfur has acidic properties. So, depending on your application in pounds per square feet and depending on your soil type, that will actually have a different effect.
So, gypsum doesn’t actually remediate soil pH because it doesn’t contain that carbonate to neutralize the acidity and it tends to be used as a fungicide and not a treatment for pH. The properties of it as a fungicide, the properties of sulfur is that it’s toxic to pathogens and can kill them through direct contact or fumigation. Essentially you add a solution of lime with additional antifungal flowers of sulfur boiled in water and the sulfur will disrupt the transfer of electrons and cause the reduction of the sulfur to hydrogen sulfide in soil. And this is very toxic to cellular proteins, and it’s also toxic to some plant species. And essentially when you add lime to this sulfur compound, it will reduce the phototoxicity. So that’s why it’s commonly called a liming substance, but it’s actually not solving pH your problem. So, it’s important to note.
Drew Lyon: Actually making it worse, it sounds like, if acidity’s your problem. Okay.
So, Emi, how do you go about calculating a lime requirement for soil?
Emi Eleccion: Yeah. So, soil laboratories first use soil pH to determine if you have a problem with soil acidity. And so, I will always recommend that you test your soil, and recommend to use a soil laboratory that’s familiar with the soil in your region.
So, if you’re in eastern Washington, obviously there’s a great one here at WSU Pullman, and with proper calibration, these results, a buffer test can calculate lime requirement. And there’s a great calculator for that on the WSU Wheat and Small Grains website in the soil tools and calculator section, where it uses things like tillage depth and target pH. Other soil properties like cation exchange capacity, base saturation, soil organic matter content, and exchangeable acidity can be used to measure lime requirement as well. The calculated requirement tells you the amount of base forming cations in the form of lime that is needed to displace the acid forming cations, like hydrogen, based on individual soils’ buffering capacity, and provides lime requirements in pounds or tons per acre.
Drew Lyon: Okay, so that website, smallgrains.wsu.edu, is where you’d find those calculators. And it sounds like it’s not an easy calculation to do on your own. So, finding a calculator is probably a good idea for most people.
So, Heidi, how would a grower choose their method of application?
Heidi Vandyk: Right. So, once you have calculated your lime requirements, there are some next steps to understand how you fully apply that lime. So, you have to consider the environmental factors that are also impacting soil pH, and a few of these are soil layering, climate, and season.
So, when considering the effects of tillage, you have to consider whether you’re using a reduced or inverted tillage methods. And this will actually change the depth and concentration of the acidity issue in your soil, so that’s why it’s important. And in reduced till systems, you will see more highly concentrated and acidic narrow bands of stratification in the topsoil.
And then inversion tillage will actually involve more soil mixing of the layers and will increase depth of the acidified layer and decrease the concentrated acidity. And when you use inversion tillage, it will require more complex methods of testing. And that’s because the mixing of soil layers will actually make the acidity problem less noticeable because that layer is thicker. So that’s why tillage will affect your application method and will affect the amount of lime that’s required to raise that pH back up.
And then the next part of that is climate. So, base cations in the soil will actually be leached in certain climates with heavier rainfall and also greater temperatures will accelerate the time it takes for a liming to actually show results. If your soil is very dry, the liming will not improve your soil pH very fast and it won’t be super uniform in your soil layer. And different soil types as well, such as silt loam and sandy soils, these tend to experience decrease yield with crops. So that’s a factor to consider. And the acidification of soil can also happen in climates with higher organic acids and also organic debris and greater atmospheric acid. So, these are all components that are important when you’re considering how much lime to apply.
And then lastly, simply put, seasonality is also a factor because pH will typically increase during winter months and will decrease in the summer. And so, depending on when you apply the lime–which season–that will also be an important factor to consider. So overall, some recommendations for those who are using liming practices, the saturation of your soil prior to liming is actually recommended so that it can fully incorporate it properly. And the sooner you can saturate the soil, the better. And when you change your liming practices, you should consider the assessment of your climate, the tillage practices, and the season of application. So, these are all factors.
Drew Lyon: Okay. And those factors would also affect, I would assume, how and when you sample for pH so you know what you have. And then, I guess, the other factor that comes in that’s kind of a moving target is just the economics of it because we don’t live near lime sources. And so, it’s kind of expensive to get lime here. But all those factors need to come together. So, it sounds easy–your soil is becoming acidified but how you go about dealing with it varies. And so, people need to understand it.
And so, it sounds like you two learned a lot during your summer internship in REEU program. Did you enjoy it?
Emi Eleccion: Yeah. A lot.
Heidi Vandyk: Yeah. It was great.
Drew Lyon: Alright. Well, hopefully we can continue that program in the future years. I’m glad you had a good time. I’m glad you shared some of that information with us today. Thanks for being my guests today.
Emi Eleccion: Yeah, thank you.
Heidi Vandyk: Thank you so much.
Drew Lyon:
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Thanks for joining us and listening to the WSU Wheat Beat podcast. If you like what you hear don’t forget to subscribe and leave a review on iTunes or your favorite podcast app. If you have questions or topics you’d like to hear on future episodes, please email me at drew.lyon — that’s lyon@wsu.edu — (drew.lyon@wsu.edu). You can find us online at smallgrains.wsu.edu and on Facebook and Twitter [X] @WSUSmallGrains. The WSU Wheat Beat podcast is a production of CAHNRS Communications and the College of Agricultural, Human, and Natural Resource Sciences at Washington State University.
I’m Drew Lyon, we’ll see you next time.
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The views, thoughts, and opinions expressed by guests of this podcast are their own and does not imply Washington State University’s endorsement.