Oct 20, 2020
In this episode, we discuss the importance of what is in our soil and how its nutrients or contaminants affect plant growth and the food we eat. Dr. Ganga Hettiarachchi, is one of the world’s leading scientists in the fields of trace metal and nutrient chemistry in soils. Hettiarachchi's research at K-State focuses on understanding the chemistry of both nutrient and contaminant elements in soils, with the goal of developing solutions to agricultural or environmental problems.
Soil Chemistry: What’s In It For Us? – food science from the ground up, with Dr. Ganga Hettiarachchi, professor in the Department of Agronomy at Kansas State University
I think current practices. Most of the time if you think about farmers, they try to do the best they can do to protect their soil. I mean, that doesn't really, they do not want to do things to harm their soil.
Something to chew on is a podcast devoted to the exploration and discussion of Global Food Systems produced by the Office of Research Development at Kansas State University. I'm Maureen Olewnik, coordinator of Global Food Systems.
I’m Scott Tanona. I'm a Philosopher of Science.
And I'm Jon Faubion. I'm a Food Scientist.
Hello everybody and welcome back. The food we eat is a product of many factors including seed quality and variety, weather conditions during the growing season, and processing and storage. But one of the most critical aspects of growing food is what it is grown in the soil. Soil provides nutrients to the growing plants through its components, which include minerals, water, organic matter and microorganisms. Additionally, soil provides a critical avenue for carbon dioxide sequestration, a major factor in reducing greenhouse gas. In this podcast, we will be talking with Dr. Ganga Hettiarachchi, Professor in the Department of Agronomy in Kansas State University's College of Agriculture. Ganga is one of the world's leading scientists in the fields of trace metal and nutrient chemistry and soils. Her research at K State focuses on understanding the chemistry of both nutrient and contaminant elements in soils with the goal of developing solutions to agricultural or environmental problems. I'd like to welcome Ganga to Something to Chew On and look forward to hearing more about you personally and about your profession.
Thank you for inviting me. So I was born and raised in a suburb of Colombo, Sri Lanka. And then when I was about to go to university, I had opportunity either to go into Agriculture Science to go into geo sciences. And my mom was leaning towards geosciences, because that means that I could go to university from home, because it was a university, the base we noted before that was in Colombo, and then the Agricultural Sciences, it was in a different city, my dad thought that doing Agricultural Sciences, more like applied sciences would be beneficial. So he encouraged me to actually take opportunity, although it was in a different city and go and do that. And then while I was doing my Bachelor's, third year, we get an opportunity to so we do sort of agriculture courses, starting from Agricultural Engineering, Agricultural Economics, to Soil Science, Food Science, Animal Science, everything pretty much. And then third year, we get a chance to select what area we want to specialize in. And then finally a fourth year we do only that and then we have six months research projects as a bachelor student during doing like 100 on a degree BSC honors degree. So I chose Soil Science, I could have gone and do some other things. Because the prospects job prospects for Soil Science wasn't that great at that time in Sri Lanka, but because my desire for Soil Science, I stick with that and I did my specialization in soil science, and I did a project related to phosphorus chemistry to my final year. And then I got a opportunity to come to US on a Fulbright scholarship to do my Masters. And I came to Kansas State University and did my Masters and stayed at Kansas State University. Same progresses. Dr. Gary Pierzynski and did my PhD in soil chemistry as well. Only difference was when I was doing my master's I did again Phosphorus Chemistry, but I changed my focus and did more like Environmental Chemistry focusing on contaminants and how to handle soil contamination, remediation focus, more specifically, incident stabilization of soil lead, cadmium and zinc. And then I took a I did a postdoctoral fellowship at USBC National Risk Management laboratory at Cincinnati, Ohio. And I went back to my university because I was actually when I was doing my Masters and PhD, I was on study leave as an assistant lecturer at the same university. I did my bachelor's, so I went back and work as a Senior Lecturer over there for two years, and took a position as a research scientist and Adelaide, Australia. So I was at the University of Adelaide and the CSIRO, Commonwealth Science and Industrial Research Organization for three years before came on to this position. So I actually replaced since Dr. Pierzynski, decided to go to Administration, I was the replacement for his position.
So you shifted when you started your masters, it was you shifted into more of the environmental side and looking at the chemistry of environmental contaminants what led to that shift?
How is it actually it's the same principle a lot of people ask me that, because I focus on soil contamination remediation, that came for my PhD and then when I was in Australia, I was again working on nutrient chemistry, phosphorus and micronutrients. It same principles only saying is, when it comes to nutrient as a soil chemist, I tried to find ways I can maximize nutrient availability to plant and synchronize nutrient availability to replant update, who couldn't have enough is again understanding chemistry of that, and then trying to minimize the bioavailability of it. For example, when I was doing my PhD, I was looking at things in Southeast Kansas and the tri-state mining area, we are seeing wholesale issue concentration was too high. So that seemed was causing phytotoxicity. We cannot get any plants to grow in those mining materials. So I was trying to see how we can minimize zinc bioavailability so that we can get grass growing and the with growing grass minimize contaminated material moving from by being by water. And then when I was in South Australia, I was looking at zinc as a nutrient, because in most of the strain in South Australia has lot of high pH, high Calcareous area soils, so zinc is not available for plan to take up. Most crops are suffering from zinc deficiency. So I was looking at things over there are two ways to maximize things bioavailability so I think it's the same principle, same understanding, just looking at depending on situation, looking at either to increase bioavailability you decrease bioavailability.
And the results of your research get promulgated out through by what way how do they actually reach the people that might benefit by it?
Yeah, so in various ways. So the when we were dealing with so the first project after I moved to K State as a faculty member, it was funded by US EPA, and that's to looking at Urban gardening, sustainable gardening at brownfield sites. So brownfields are actually sometimes not necessarily contaminated, maybe mildly contaminated, but because of perceived contamination is abandoned or underutilized. So looking at those kind of soils, and then how to get those to put into urban gardening or some other use. So in that project, we actually directly dealt with communities. We chose the Brownfield sites to establish our test plots, working with communities, so we had that direct community involvement, as well as other part of it for research, research, technical assistance, kind of programs to we needed to work with communities, we made a lot of the factsheet for people to use, as well as we did lots of workshops, different places. So through workshops and things like that when I was in Australia working on micronutrient and ways to enhance micronutrient availability. We use again, journals that, oh, the magazines actually goes to farmers. So I remember when I receiving sometimes directly phone calls from farmers, actually, just before they are deciding to apply fertilizer, asking me why I think that liquid would work better for their soils compared to granules. And I had that similar experience over here. After one of my PhD students, like most recent papers, Jay Weeks will know Him. And then I got an email from a farmer named Brisca. Asking about, again, the same type of questions. So I think sometimes it's great again, that that person like that was published in the recent paper was published in Science Society of America journal, that's not what actually reads the farmer, based on that case are the key sorry, the the kind of intervene, I think that was what elegent farmers so I think they we do need to be do we should not think that publishing in, although that is our goal, progressional goal to publish in peer reviewed journals. But at the same time, we do need to do those kinds of interviews, those kinds of workshops and things like that, so that information will get to farmers, gardeners, who in uses.
I was just going to ask you were talking about the Brownfields and identifying contaminants in inner cities and those types of things. Did you get to the point to where you were working with actually cleaning those up? How does that happen? How do you clean up an area once it's contaminated that way?
So the then doing brownfields work, we were supposed to actually not just go to any brownfields. The EPA grant required us to actually go to brownfields where communities intend to have decided you can convert that to transform that into an urban garden or a community garden. So we work with those communities to assess thing when we were doing that process, since we cannot actually test everything under the sun to we do some kind of history information, trying to gather industry information, using Sanborn map, talking to neighbors talking to community and then then trying to kind of narrow down what things need to be tested. And we had seven sites within that project. And first site was in Kansas City, Missouri and then the second site was Tacoma, Washington, Seattle, Washington, and then site was Indianapolis, Indiana, one was Pomona, California, and then we had a sighting feeling as well to all those places after talking to them we sometimes we only tested for inorganic contaminants, because we found that the most common contaminants most common contaminant been those brownfields thats lead. Sometimes it was lead and arsenic sometimes it was we thought that cadmium is also another common contaminant, but we did did not find it by contaminated with all three and Indian qualified we found in addition to lead arsenic, we found polycyclic aromatic hydrocarbon concentration to be elevated as well. So, depending on site see what we found were different. And then if it is organic contaminant more and then we try to see what other ways to degrade that enhance degradation of that, but with inorganic contaminants, we were not trying to remove thee they are not degrading they are they are most of these inorganic contaminants are persistent. Only thing we can do is we can look at ways to transform the those into less mobile for more or less bioavailable form. So useful amendments and use other understanding about that particular chemical and that particular soil and treat are try best way to keep it in place. So that it will not move from soil to plant. And in any way. The something like lead is not something easily moving from soil to plant. Even if it's more it actually stays in growth rather than moving from room to shoot. So the understanding how they behave in soil and how they behave in plan, like the uptake and all that we can decide what's the best approach?
And do you set when you go into a site? Do you set specific thresholds that you would consider these sites that ought to be remediated? Or how are those…
So how that works. So we do know that when soil lead concentration, so if you look at EPA, the residential swill lead limit is 400 milligrams per kilogram. But that was determined, we decided, based on 10 micrograms per deciliter of children's blood lead concentration. In 2012, the CDC had a group of scientists looking at all the health sciences looking at all the effects of a bad lead on children health. And the recommendation was that no blood level is safe for children. CDC cannot go, I mean, going forward two micrograms per deciliter is not practical. So they went with this 95th percentile, which was five micrograms per deciliter limit. And currently CDC is in considering to actually bring it down further to three micrograms per deciliter. So, after CDC is the change from 10 to five, actually, EPA did not do any kind of change to the residential soil lead limit. But we all know that based on to whom we talk to me know that this this concentration of soil lead could be 150 200. But again, as a soil scientist, I know that the what really matters is not the total concentration, you could have even 400 to 400 or higher, so lead by the city is not bioavailable, then it might be safer than a soil with 159 milligrams per kilogram of lead. But but but the lead is bioavailable. So I know, I think that what we use is not the total concentration, we look at total concentration because that's what mostly people want to know. But at the same time we make decisions based on bio accessibility. Because bio accessibility is we do have tests, proven tests with animal to animal feeding studies, that we can mimic gastro intestinal dissolution of soil lead, and then determine what's the the amount of lead that can be bio the maximum amount of lead that can be bio accessible to human child or the adult human if they accidentally ingest that soil to other decisions we made based on both?
And are these treatments, radiation treatments that you would apply to the soil? Are they if this were to roll down to the level of the producer? Would it be the gardener or the farmer or the land owner or teller would they be the ones that would be having the responsibility of doing these treatments?
Yeah, so yeah. And then most of the time these soil amendments as is towns are things that province will gardeners use. For example, when it comes to that it's it is phosphorus to all of us use phosphorus as fertilizer and fertilize other garden I mean loans and everything with phosphorus. So, the reason phosphorus is the most effective treatment for to reduce lead bioaccessibility phosphorus can induce formation of lead phosphate and specific group of lead phosphate known as Title Five and that has very little solubility even if it is subject to very acidic summer conditions. So So phosphorus or either depending on soil properties, we may not be directly recommending to use straight fertilizer. It may be that the organic source of phosphorus, organic source of phosphorus that slowly releasing phosphorus and maintaining phosphorus in a high enough level to promote these kinds of transformation and reduced bioaccessibility of lead, because you know that phosphorus has two sides. So these kinds of benefits are they are it's a fertilizer plant with two compete their lifecycle to we need to maintain good, good phosphorus levels. But at the same time, the phosphorus nitrogen ending up in surface water can cause eutrophication. Considering all that some of those sides, if we find that the extractable levels of phosphorus is already high than what we recommended could be slow releasing fertilizers mostly like organic, like, like compost. Did I answer your question?
Yes, you did. Thank you very completely.
I know that you had mentioned the Dr. Jay Weeks a little bit earlier. And I've visited with him in the past, actually, he was one of our hosts for a period of time. And we talked a lot about sequestration of co2 and with global warming and everything we know about co2 in the atmosphere. Can you tell us a bit about how that system works? And is that something that you're working on as well?
Yeah, I work on it. And before I had a PhD student and actually working on entirely that over PhD, and then if we look at why we are interested in a carbon soil carbon sequestration and so it depends on the AVI looked at what the carbon dioxide concentration in the atmosphere and what's the carbon dioxide concentration and a carbon concentration in the an organic carbon specifically in the top one meter of soil. And then you see that the top one to one meter of soil contains organic carbon two to three times higher than what we have in the atmosphere. And then simply will do we know that the geologic carbon tools can be much high and then the other marine and environment carbon and can be high, but if you consider why we consider as soil carbon sequestration as a mitigation efforts, the soil is in direct contact with the atmosphere. So soil can be a simple source for carbon. So I do know that the soil can be your thing to the photosynthesis and photosynthesis processes using carbon dioxide and water, when sunlight is there to convert inorganic carbon to organic carbon, and then this organic carbon gets into soil. And then the part of it can be composed and release carbon dioxide back. And at the same time, there can be waste with this carbon this because the organic carbon actually going to be part of what we consider as soil organic carbon or the humors. And then finding ways to keep this carbon in soil longer, longer. We consider the call as carbon sequestration. So the I was interested in like, I'm always interested in understanding basic, like mechanisms. My whole research interest is understanding mechanisms of any processes that I'm interested in. So, we were interested in looking at the temperate soils like Mali soils from that was Dr. Chuck Rice's Long Term field study is actually close to 30 years now. And at the time we sample it, it was over 23 years, and I post on the continuous court. And they had these treatments, different levels of nitrogen fertilizer, and also to two different sources of nitrogen fertilizers. And then looking at the carbon sequestration mechanisms, like how carbon getting sequences, how soil mineralogy can impact that sequestration. And then also we compare that system with a long term field studies about that long, more than 22 years long study from Brazil as well, because soil types are different. So no farm soil that was a Mali soil. And then we consider those soils that are relatively younger. And then when we consider the Brazil that soil goes and oxic souls and that was highly weather and high in iron, aluminum and manganese, oxy hydroxide. So there are mechanisms. When we look at carbon sequestration mechanisms, you could see that more influence from a mineralogy and it doesn't mean that when you go to moleculer levels and looking at that level, even in Mali soil they're both in their contribution from mineralogy. So initial contribution from mineralogical evidence And in both systems, again, you know that the all of us as researchers, we have interest. And then sometimes depending on funding, we move from one to another to at the moment I do not have active projects that looking at carbon sequestration. But I am always interested in that aspect of the potential of soil to the carbon soil carbon sequestration to be mitigation efforts for climate change.
Is this something that takes a little bit of doing to get farmers to buy into the idea of changing their methods to to help enhance co2 sequestration? Is it something where they're going to have to change what they're doing? Or are there current practices that will work well into that?
I think current practices, most of the time. If you think about farmers, they try to do the best they can do to protect their soils. I mean, that doesn't really they, they do not want to do things to harm their soils. So the those both those studies, I mentioned, one in North farm and the one in Brazil, actually both had killed and Northfield system that we compare. So you know that no note here low reduce tail is something that farmers moving towards most farmers, it's hard for us to find feel sometimes that continuously. So the no till practices, adding the residue back into soil, use cover crops, and all sorts of those things that you mean opportunities for farmers to increase, soil carbon levels increase, as well as not just increase temporary but but maintaining good soil carbon levels. That's something farmers actually willing to do, I think, not just you know, having incentives by having an incentive, definitely will help. But you can see the incentive, I actually read recent articles related to getting prairies to enhance carbon sequestration, and Texas and they were talking about how that can work, how the farmers to keep those things or how people to maintain those kind of natural areas, as is goodwill college, because the public company is they are looking for ways to get carbon clean. So maybe they can work with people who are maintaining prairies and contribute into this carbon sequestration, reclaiming carbon so they can work together. So there can be not not just government incentives, there can be like private entities that are willing to work with and do this kind of creating carbon trading. So those kinds of things could work, I think farmers why they would consider doing this because they know that if they can maintain good organic carbon concentration in soil that would enhance microbial activity. So that is promoting nuclear cycling, and then promoting nuclear cycling, meaning that the amount of fertilizer inputs are going to be reduced over time. So there are a lot of positive things that farmers going to gain by doing it. And then this carbon sequestration is actually part of soil aggregation as well, too. If you improve soil aggregation to the then that will improve a lot of other physical properties as well. So the the AI and water movement in soil so I think it's a win situation for farmers. It's something that's going to improve their soils and into their soil productivity in the long run.
Are there parts of the world that have a greater need for this kind of approach than others if we you know, we talk about the Southeast important part of Kansas, but if we look globally, are there areas?
Yeah, I think if we look at like Africa and the other soils like, very deficient in carbon, the end then they may not have that many sources, but they could consider the conservation type of agriculture management practices to preserve carbon in soil and enhance carbon in soils. So yes, the highly weathered soils and then the drier areas, the arid and semi arid climates. If you find less carbon in soil to that will be more beneficial, even more beneficial for those farmers to do those kinds of practices.
So I was wondering back to thinking about contaminants, I was wondering if you're talking about processes to do to make inorganics less bioavailable, I was wondering if there are things that people do to their soil that actually do the reverse that make things worse. You know, that set up the mechanisms set up mechanisms that actually make those inorganics uptake into uptake into the crops more than they would have otherwise.
Yeah, so the we sometimes do it intentionally. So we call it pride extraction. That's a method of phyto remediation. phyto remediation is in general, meaning like using plants to remediate soils, sediments or water, sometimes we intentionally try to remove use plants to remove contaminants from soil, it does work for some contaminants, but not folk, highly mobile contaminants like lead. So for something like lead, it's more effective to try to introduce stabilize it, for them trying to extract it. So the attempt to enhance lead uptake by adding EDT, to the key leading the enhanced lead solubility by acylation and getting plants a carb, but no matter what, since plants are not taking lead, that much what happens when you add something like that to enhance the photo extraction, you would put that I mean, that lead can be subject to maybe moving downward or moving elsewhere to so that could be problematic. So that's why we do need to understand how we can deal with each of these contaminants. And each of those situation like what's the best way to handle it, but the something like arsenic for example, they are raw group of plants, we call that like hyper accumulators, that means they can accumulate these contaminants higher than normal plants would do. And then, so, those kinds of hyper accumulators would allow us to do that clean up, like use plants and grow plants for some time to do the cleanup. But if you do, but unfortunately, that doesn't work that well for most trace elements, contaminants, most trace elements are the zone to soil follow is very strong. So they uptake is very low. And then even if you find a hyper accumulator, you know that the removal is going to be dependent on not only how much they can accumulate in their plant, but also the biomass. So, most hyper accumulators will do their high packing laters meaning that they can have like a high concentration in their tissue, but they are not really a large biomass producers. So, if you do calculations, it can take a long time to do the cleanup, it may take 20-30 or more years to do the cleanup, but still, if you want to do that kind of cleanup, so, that would be the situation where we tried to do enhance availability, so that plants will take up and to your question, if you asked like can we make it more bioavailable, so, it ended up being food crops or something which we do not find? It can happen if we do it without understanding that particular soil. I think it can happen if we try to just do it without understanding the situation of soil. I can give you a example if you look at arsenic, arsenic is something that we are very much concerned about. And you see that people talking about some moss and it came out but Jews or somebody making apples or making rice and things like that. And then one thing I want to tell you that arsenic, lead and all other potentially toxic trace elements, they are naturally present in soil. So there's nothing called like positive lead positive, arsenic positive or negative because it's everywhere in various, you know the concentrations that are not harmful to us in most cases. And then in the air we breathe Again, if what matters is the concentration, is it a ball concentration that's going to harm us. So, if it is not higher than that, then then we are not concerned. So, same thing in waters in water you find these three potentially toxic trace elements in very small quantities. So, consolidation, so, we are concerned if it is a bottom the drinking water who the that motor quality standards. So, if you take arsenic is less bioavailable under oxic conditions. So, that means like the urban gardening Oh, we are the corn no we to any kind of gardening we do the latest soils in the biome because arsenic under that condition arsenic is going to stay as arsenic five and we do know that arsenic five species do chain by soil colloid and then they are by they are not bioavailable, but if you consider rice paddies and that is grown and then soils underwater. So, when soils and the water then the there's less oxygen going in and then the the whatever the oxygen labs can be consumed by microorganisms and then soon after about 10-14 days after the submergence, so it will become in like sub toxic to anoxic, under that as some toxic or non toxic environment those these Robotnik because I am Iron is a good Kevin iron oxide is a good scavenger for arsenic. So, the iron oxides and hydroxides can undergo reductive dissolution, the dissolution actually induced by reduction of irons. So, that these arsenic can really and then actually cool So, this release arsenic in five form can reduce into arsenic three, and then the arsenic retention to soil Polo is less than the arsenic five and even if it's routine, it's not actually retained via stronger the mechanisms. So, they can be they can become easily more bio available and then under under toxic conditions the arsenic availability can be high, but then again soils turning into an anoxic conditions more or less no oxygen under that conditions arsenic can get the sunlight and it can get people to the into sulfides and become a less available. So, so, so, I so, I think we do need to understand what the situations we are dealing with, and then understand the chemistry of soil understand the behavior of that particular contaminant. So, organic or inorganic contaminants of interest, and then then then think about things through that, how we can better manage it better, better manage it,
When you've got a contaminated soil, and you've talked about a few ways of mitigating some of that contaminants being taken up into the plant. Do you have when the soil is taken care of? And you're, you're mulching it? You're adding composted soil on top of that and working it in? Do you have a dilution effect over time there that will help mitigate just total quantities of material that's in there.
Thank you for bringing that back point. That's one thing I forgot to mention before. So, the things about why we sometimes go with those organic sources other than direct fertilizers, if you think about composed to any other organic source, we add in high quantities. So sometimes like 1/3 or one food by volume to offer 15 centimeter soil so and then mix it well. So, the immediate benefit that farmers get from that kind of application is the dilution effect. Sometimes dilution effect can be very high, and depending on the amount you make, and it can be to the 40% of dilution, then you do it that so and then maintaining that not by adding every year, but adding it every three months in every meal. So farmers can maintain that dilution in two years, the adding high quantities of organic matter will that would be the immediate benefit that farmers going to get and then the transforming into less bioavailable forms. Sometimes take time. And if it is a soluble P we are adding, we know that it can be quiet. I mean, it's relatively fast, but again, it depends on wheels. Late availability, because a lead is not available for plan to take off, could be the lead is not available for phosphorus react either. So because of that leads and those reaction can take place, take time. But the immediate benefit of adding something like organic matter would be dilution.
Well, as John said, this is a very, very complicated topic, but it's probably as critical to our food supply as any soil, if the soil quality is not there, the crops are not going to grow appropriately. And so that's just a fascinating area.
If you look at, we are looking at so we were originally going with a FAOW2 standard and those cortex limit, who lead concentration in any type of vegetables, but if the started looking at those by themselves, but at the same time, sometimes you see that these initial numbers coming out of scientifically, there's no base. Unfortunately, those could be completely decided by like toxicology tanpoint. And as some of you have food scientists, so you know that everything in food is not bioavailable, so we have to kind of consider that as well, especially when you are developing these types of standards. So that's a complete subject area that we can talk.
That is that is another complete subject area. And yeah, many times regulations are set, not necessarily based on based on the science that that's needed to set them behind it.
Yes, absolutely. Very intense learning situation. For me, certainly, like, I was probably one of those people that thought that soil was just something that held the plants, you know, physically.
I've learned I've learned with soil scientists, you do not call it dirt do not call it. So,
I was going to say that soil is very important for environmental quality. So the one of the causes I am teaching environmental quality, something that I tell my students this school is you can expect to learn about environmental quality, from the perspective of a soil scientist to how soil can how much may rely on soils, you know, not only to like group plans, and you know, provide that way but and then sometimes our objectives could be like holding a building or some something completely different. But at the same time, a lot of if we look at like these recycling, we expect soil to do lot of things, you know, feel the contaminants, degrade contaminants, and protect, cover groundwater, and then protect cover surface waters, and then with carbon mitigation and other efforts, and then help with global climate change. I think I think there's a lot that we can do,
And much more dynamic system that people appreciate.
Yes, speaks nicely to the global food systems approach towards interdisciplinary research. It touches on so many things and there's so many areas that work into it.
If you have any questions or comments you would like to share check out our website at https://www.k-state.edu/research/global-food/ and drop us an email.
Our music was adapted from Dr. Wayne Goins’s album Chronicles of Carmela. Special thanks to him for providing that to us. Something to Chew On is produced by the Office of Research Development at Kansas State University.