Impact of Land Use on the Storage and Turnover of Soil Organic Carbon: Stories from the Subsoil.
Michael Kaiser, Asisstant Professor for Applied Soil Chemistry, Department of Agrnomy and Horticulture, University of Nebraska Lincoln
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05/25/2024
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Land use change is one the main drivers of organic carbon storage in soils but significant knowledge gaps exist towards the response of biogeochemical cycles in the subsoil. In this seminar, I will present and discuss data from more than 20 sites in Nebraska. At these sites we sampled soil under cropland, native prairie or forest down to depths of at least 3 meters. The samples were analyzed for carbon storage and turnover, ecologically relevant carbon fractions, microbial community structure, and soil mineral characteristics. The data of these analyses can help to develop improved land use strategies to increase the long-term carbon storage beyond the topsoil.
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- [00:00:00.750]The following presentation is part
- [00:00:02.670]of the "Agronomy and Horticulture" seminar series
- [00:00:05.790]at the University of Nebraska Lincoln.
- [00:00:08.416]All right, so thank you for coming this morning.
- [00:00:11.670]I think we have a really exciting presentation ahead of us
- [00:00:14.670]for our today's seminar.
- [00:00:16.530]So a few housekeeping items before we get going.
- [00:00:19.470]As I mentioned just a moment ago,
- [00:00:21.480]we have food and beverage in the back.
- [00:00:24.330]Feel free to grab a snack, get some coffee.
- [00:00:26.250]Most importantly, make sure none of this left
- [00:00:28.410]by the time we're done here today.
- [00:00:31.200]Another thing, please hold your questions
- [00:00:34.710]until after the seminar is done
- [00:00:36.900]or when we have the Q&A session.
- [00:00:39.030]And then also thirdly,
- [00:00:41.220]for those of you who are in the room here,
- [00:00:43.320]when you have a question
- [00:00:44.340]please wait to receive the microphone
- [00:00:46.140]before you start asking your question.
- [00:00:48.030]That way our audience members online
- [00:00:50.070]are able to participate in the conversation.
- [00:00:53.460]So our seminar speaker today is Dr. Michael Kaiser.
- [00:00:57.030]Dr. Kaiser is an assistant professor
- [00:00:58.980]of Applied Soil Chemistry here in the Department
- [00:01:01.620]of Agronomy and Horticulture.
- [00:01:03.300]He has over 20 years experience in teaching and research
- [00:01:07.440]and soil chemistry and organic matter dynamics.
- [00:01:10.800]And this has really taken him back and forth from Germany
- [00:01:14.430]over a number of years here.
- [00:01:16.380]He's done works at the University of Potsdam
- [00:01:18.990]Leibniz Center for Agricultural Landscape Research,
- [00:01:21.630]University of California, Merced,
- [00:01:24.120]university of Kassel, and here at UNL.
- [00:01:27.120]And during his adventures, he is been able to collaborate
- [00:01:30.090]and work alongside many world renowned scientists
- [00:01:33.330]including Horst Gerke at Leibniz,
- [00:01:36.150]Asmeret Berhe at Merced,
- [00:01:38.370]and then Rainier Joergensen
- [00:01:40.980]and Bernard Ludwig at Kassel
- [00:01:42.450]among many, many others.
- [00:01:44.370]So it's my great pleasure and honor
- [00:01:46.290]to introduce our speaker today, Dr. Michael Kaiser
- [00:01:50.160]and his presentation on "Carbon: Stories from the Subsoil".
- [00:01:53.890]Floor is yours, Michael.
- [00:01:55.770]Thank you very much.
- [00:01:56.670]Thank you very much for coming and for being here
- [00:01:59.370]and giving me the chance to show a little bit of my work
- [00:02:02.400]that we've done over the last couple of years.
- [00:02:04.677]And I'm especially excited to see a lot of students actually
- [00:02:08.688]who took my carbon nitrogen class, right?
- [00:02:12.570]So thanks for coming
- [00:02:14.190]and I'm expecting tough questions, right?
- [00:02:17.040]So you are the experts.
- [00:02:18.720]Okay, so we are talking about
- [00:02:21.727]"Impact of Land Use and on the Storage
- [00:02:24.360]and Turnover of Soil Organic Carbon:
- [00:02:26.297]Stores from the Subsoil".
- [00:02:28.410]Thanks for the introduction.
- [00:02:29.880]So I can skip the line next one.
- [00:02:32.220]So why do we care?
- [00:02:33.720]So, so organic carbon is a key parameter
- [00:02:36.360]for functioning of soils.
- [00:02:38.490]So we have an effect on water storage and quality,
- [00:02:42.180]an effect of nutrients, storage and supply
- [00:02:45.360]on structure and aggregate.
- [00:02:46.860]So more carbon is reducing the densities of compaction
- [00:02:51.300]and it's helping preventing erosion.
- [00:02:53.850]We know it's gas storage, right?
- [00:02:55.770]Soil organic matter, carbon dioxide,
- [00:02:58.170]but all but also N2O.
- [00:03:00.598]So we have as more soil organic matter,
- [00:03:04.080]soil organic carbon we have
- [00:03:05.610]as more greenhouse gases we store.
- [00:03:08.220]It is in habitat for microorganism
- [00:03:11.100]and important for their productivity and wellbeing.
- [00:03:14.940]And it is a coupled biogeochemical cycles
- [00:03:18.690]to nitrogen and contaminants.
- [00:03:21.300]So we have a couple of major environmental
- [00:03:23.580]and anthropogenic factors that control
- [00:03:25.980]soil organic carbon and organic matter dynamics
- [00:03:28.920]and that is soil mineral characteristics and soil type.
- [00:03:32.250]So stuff like clay content, amorphous iron oxides,
- [00:03:35.910]aluminum oxides, cations, that is stuff
- [00:03:39.630]that sites specifically affect your carbon storage
- [00:03:42.960]but also your carbon turnover.
- [00:03:45.570]So use the big three categories,
- [00:03:48.930]arable, forest, grassland and a little bit.
- [00:03:53.685]So on the rising also for recognition,
- [00:03:58.260]urbanization and soil management.
- [00:04:00.690]What do we do with our soil, right?
- [00:04:02.520]Tillage, do we add biochar?
- [00:04:04.230]Do we add mineral fertilizer, organic fertilizer and so on.
- [00:04:08.277]And so our management activities do have
- [00:04:11.370]a large effect on our soil organic carbon dynamics,
- [00:04:14.250]and soil depth, right?
- [00:04:16.350]So that's a little bit the focus of this talk.
- [00:04:18.900]We are not just looking in the topsoil,
- [00:04:20.820]we are looking specifically in the subsoil.
- [00:04:23.820]So that is last 2000 years.
- [00:04:26.400]Intensification of land use and carbon loss, right?
- [00:04:32.130]This land, big land use change patterns.
- [00:04:35.220]So intensifying agricultural
- [00:04:37.110]or land use intensity led to a mean loss
- [00:04:40.590]of 26% in the upper 30 centimeters
- [00:04:43.617]and 16% within the upper top 100 centimeters.
- [00:04:48.690]And to understand this,
- [00:04:50.337]the soil stores more carbon
- [00:04:52.410]than biomass and atmosphere together
- [00:04:55.350]and small changes in soil organic carbon
- [00:04:57.930]on the plus and on the negative.
- [00:04:59.640]So losing and gaining does have an effect
- [00:05:02.370]on our carbon dioxide stored in the atmosphere.
- [00:05:05.490]So that is a big pool in terrestrial carbon cycle.
- [00:05:10.830]Why do we care about the subsoil?
- [00:05:12.660]So more than 70% of this global soil organic carbon is
- [00:05:16.217]in the subsoil.
- [00:05:17.370]Here defined below the A-horizon.
- [00:05:20.040]There are other definitions
- [00:05:21.330]below 10 centimeters or 30 centimeters
- [00:05:23.610]that depends who we are talking to.
- [00:05:25.560]I general like to talk about horizons
- [00:05:28.260]because there are biogeochemical boundary conditions.
- [00:05:31.500]So horizons in soil are there for a reason
- [00:05:34.590]and they tell us a lot about the soil, how it's functioning,
- [00:05:38.100]where we see changes in characteristics.
- [00:05:40.830]So I like to follow in my research mainly soil horizons.
- [00:05:46.320]Then there was a study in 2015 saying
- [00:05:49.830]90% of 360 studies,
- [00:05:51.960]analyzed in two review articles published 2000.
- [00:05:55.080]So they are cited more than a thousand times
- [00:05:58.110]about the impact of land use on soil organic carbon,
- [00:06:00.600]sampled only to a depth of 30 centimeters.
- [00:06:03.630]So our knowledge about topsoil carbon is
- [00:06:07.470]increasing exponentially.
- [00:06:10.320]The knowledge about subsoil is you know,
- [00:06:14.670]hanging behind, trailing behind, right?
- [00:06:16.620]So there are much less studies
- [00:06:18.390]about subsoil than about topsoil carbon.
- [00:06:23.070]So that means better understanding of factors,
- [00:06:25.290]processes and mechanisms that drive soil depth.
- [00:06:28.110]Specific differences in carbon stocks,
- [00:06:30.360]stabilization and decomposition is and critical need
- [00:06:34.080]for management decision, modeling efforts
- [00:06:36.510]and carbon budgets.
- [00:06:39.510]Okay, that brings me to my first case study.
- [00:06:41.910]So here that is a project we did back in Germany,
- [00:06:45.330]zero to two meters.
- [00:06:47.400]That was kind of the reason
- [00:06:49.560]why I caught interest in the sub soil carbon dynamics.
- [00:06:53.280]So that was about five sites in central Germany,
- [00:07:01.290]five different soil types, limestone, red sandstone,
- [00:07:04.380]so that's apparent material basalt, tertiary sand and loess
- [00:07:07.740]and a beach forest on each of them.
- [00:07:11.100]The beach forest was older than 95 years,
- [00:07:13.290]so we assume some kind of steady state conditions.
- [00:07:18.090]And then that is a depth distribution.
- [00:07:20.580]So this went, so we have an A-horizon B1, B2,
- [00:07:23.910]here we get down to the C-horizon.
- [00:07:26.790]So you see we had one side down to 50 centimeter
- [00:07:30.780]to other sides to 80 centimeters.
- [00:07:32.730]And this was tertiary sand
- [00:07:34.440]and loess down to 170 centimeters.
- [00:07:38.490]So what we did, we analyzed,
- [00:07:41.190]so clay content 30 to 40.
- [00:07:45.150]So we had a big difference of variability in clay,
- [00:07:49.380]iron oxides and aluminum oxides that is important
- [00:07:53.130]for different stabilization potential in soil.
- [00:07:58.290]So the more the better for stabilization.
- [00:08:00.720]And when I talk about stabilization
- [00:08:02.400]then I'm talking about protection of organic matter
- [00:08:05.460]against microbial decomposition.
- [00:08:07.860]So stabilization is a process, right?
- [00:08:10.170]So it makes the available organic matter
- [00:08:14.490]that microbes like to decompose for energy purposes
- [00:08:17.910]and release CO2.
- [00:08:20.010]And then we have protection mechanisms.
- [00:08:21.720]And if I talk about stabilization,
- [00:08:23.430]I mean the protection mechanisms
- [00:08:25.230]that prevent this organic matter
- [00:08:27.090]from being decomposed by microorganisms.
- [00:08:31.770]So then we did a fractionation,
- [00:08:34.110]so actually we did two.
- [00:08:35.700]One was aggregate fractionation.
- [00:08:38.640]So we went from marco-aggregates
- [00:08:40.350]down to aggregate smaller than 53.
- [00:08:43.971]And the reason behind this, smaller the aggregates
- [00:08:47.220]are getting the size of the banning agents is smaller
- [00:08:51.090]number of interactions per mass aggregated material gets up,
- [00:08:56.100]mechanical stability gets up
- [00:08:57.990]and that is the mean residence time of occluded
- [00:09:01.110]organic matter gets up as well.
- [00:09:02.640]So means as high as this mean residence time
- [00:09:05.520]as more stabilized it is.
- [00:09:07.620]So if I'm talking
- [00:09:08.453]about the mean residence time of 100 years,
- [00:09:11.220]I would mean that it takes 100 years
- [00:09:13.500]to exchange each carbon atom
- [00:09:16.050]and this fraction is at least one.
- [00:09:18.570]So as higher the mean residence time
- [00:09:20.520]or as higher the turnover time
- [00:09:22.560]as more stabilized this stuff is.
- [00:09:24.990]And here we assume getting smaller aggregates would,
- [00:09:29.460]we would see here the organic matter
- [00:09:31.830]with the highest stabilization
- [00:09:33.120]and highest mean residence time.
- [00:09:35.880]Then we also use a density fractionation
- [00:09:37.830]that looks a little bit in different parts
- [00:09:40.320]of this soil organic matter pool,
- [00:09:42.360]which is generally very heterogenic, right?
- [00:09:45.030]So soil organic matter is,
- [00:09:47.150]consists of different pools of fractions.
- [00:09:50.460]So organic particles, dissolved organic matter,
- [00:09:53.880]aggregate occluded organic matter
- [00:09:55.590]or organic matter attached to mineral surfaces
- [00:09:59.250]and especially the organic matter
- [00:10:01.230]attached to mineral surfaces
- [00:10:02.790]and occluded in small aggregates,
- [00:10:05.250]there we see in high stabilization.
- [00:10:07.020]So that's our stabilized organic matter.
- [00:10:09.960]So in here we see as well,
- [00:10:13.290]so not aggregate occluded plant particles,
- [00:10:16.830]aggregate occluded plant particles
- [00:10:18.540]and mineral associated organic matter
- [00:10:20.280]by a density fractionation.
- [00:10:22.110]So the heavy fraction is assumed
- [00:10:24.480]to recover the most stabilized organic matter.
- [00:10:29.340]So when we did also we analyzed microbial biomass,
- [00:10:33.510]we analyzed carbon dioxide, we spied within 14 days.
- [00:10:37.620]That gives us an estimate
- [00:10:39.000]about the easily available organic carbon,
- [00:10:42.030]the amount that gets easily decomposed.
- [00:10:44.820]So microbes have immediate access
- [00:10:47.580]and decomposed it within 14 days.
- [00:10:51.000]What we also did,
- [00:10:51.833]we did DRIFT spectra of our fractions.
- [00:10:54.150]So that gives us information
- [00:10:55.500]about C-H groups relative abundance
- [00:10:58.230]and relative abundance of C-O groups.
- [00:11:00.780]So that's carbonyl and carboxyl groups.
- [00:11:03.750]And if you build the ratio the B over A ratio,
- [00:11:07.080]that means if this ratio is increasing,
- [00:11:09.660]your amount of oxygen
- [00:11:12.450]containing functional groups is increasing.
- [00:11:14.670]So that is a C-H material methylene bond.
- [00:11:17.610]That's hydrophobic, that's hydrophilic.
- [00:11:20.280]And this groups,
- [00:11:21.510]this intensity is increasing with microbial processing.
- [00:11:24.930]If you have an oxidative breakdown of organic matter,
- [00:11:28.290]the C-O group is increasing
- [00:11:30.120]because that is adding oxygen
- [00:11:32.670]to your decomposed organic matter.
- [00:11:35.430]So as more it is microbially processed
- [00:11:38.730]as more C-O groups you have
- [00:11:40.257]and as higher gets this B/A ratio.8
- [00:11:42.777]And that is important because it's not like
- [00:11:46.560]that you have a chunk of organic matter
- [00:11:48.180]and all of a sudden you have CO2, right?
- [00:11:50.580]So there might be 100 or 200 or 300 cycles of decomposition
- [00:11:54.060]that the microbes just decompose a little bit
- [00:11:57.120]and leaves the rest behind.
- [00:11:58.770]Or just release the decomposition products
- [00:12:04.290]that are not fully converted to CO2.
- [00:12:07.160]And this microbial processing converts
- [00:12:09.120]plant-derived organic matter
- [00:12:10.650]into microbial-derived organic matter.
- [00:12:13.110]And then you have, on the other hand,
- [00:12:14.460]you have also dead microorganisms
- [00:12:16.770]that do have a lot of carboxyl groups
- [00:12:19.080]and their surfaces, right?
- [00:12:20.940]So if you have more C-O groups, then you see
- [00:12:24.870]and more intense microbial processing, right?
- [00:12:27.690]So decomposition over time, microbial processing,
- [00:12:31.230]getting a little bit more this functional groups
- [00:12:36.480]which also increase the reactivity of the organic matter.
- [00:12:39.450]So the organic matter gets smaller
- [00:12:41.700]and it does have more functional groups.
- [00:12:43.467]And this functional groups are important
- [00:12:45.540]for interaction with mineral surfaces, right?
- [00:12:48.150]Always building aggregates.
- [00:12:49.920]So you're making it smaller
- [00:12:51.570]and you're making it more reactive
- [00:12:53.520]and then it has more chances to interact with minerals
- [00:12:56.760]to build up this mineral associations and aggregate.
- [00:13:01.080]Okay, what did we find out?
- [00:13:02.640]So that are five soils.
- [00:13:07.560]Here are the sampling depth
- [00:13:10.050]and not really surprisingly the bulk soil carbon,
- [00:13:15.120]carbon in microbial biomass
- [00:13:16.950]and carbon respired CO2 is decreasing.
- [00:13:19.950]So that is gram or milligram C per kilogram soil.
- [00:13:24.030]The same happened for organic carbon
- [00:13:26.310]recovered in our different fractions.
- [00:13:28.110]So with soil depth, the concentrations go down.
- [00:13:32.040]That is not surprising.
- [00:13:34.170]That again, that's very busy.
- [00:13:35.730]But five different soils,
- [00:13:38.526]two depths, three depths, four depths.
- [00:13:42.450]And here the aggregate fractions
- [00:13:44.580]and here the density fractions,
- [00:13:48.210]the last one that's smaller 53, that's a heavy fraction.
- [00:13:52.830]That is a stabilized organic matter, right?
- [00:13:55.220]So that is mineral associated,
- [00:13:57.360]mineral associated and occluded in small aggregates.
- [00:14:02.580]So the percentage goes up.
- [00:14:05.610]So with deeper going in the soil,
- [00:14:08.910]the percentage of mineral associated organic matter goes up,
- [00:14:12.930]bulk soil goes down, but the percentage that's stabilized
- [00:14:16.500]or recovered in the stable fraction goes up, right?
- [00:14:20.460]So percentage of organic carbon stored
- [00:14:24.270]in heavy fraction smaller 53 is increasing with soil depth.
- [00:14:28.920]So the relative proportion of organic matter
- [00:14:30.930]stabilized by micro aggregation
- [00:14:32.910]and mineral association seems to increase with depth.
- [00:14:37.080]That's why our FTIR data is the same structure
- [00:14:41.400]that here is the the B/A ratio.
- [00:14:46.070]So that's not really a unit, so it's unit less.
- [00:14:49.230]But what you see is that the B/A ratio is across fraction
- [00:14:53.040]and across sites is increasing.
- [00:14:56.010]So this B/A ratio,
- [00:14:57.300]which gives you an an estimate
- [00:14:59.130]of carboxyl and carbonyl groups, right?
- [00:15:03.480]This relative abundance is increasing
- [00:15:06.030]and almost all fractions going down.
- [00:15:09.150]So that means that the B/A ratio
- [00:15:12.630]across aggregate, density fraction is increasing
- [00:15:15.090]with soil depth
- [00:15:16.170]and ongoing microbial processing with depth
- [00:15:19.530]for organic matter in all fractions and
- [00:15:21.690]all selective downward movement of microbial process,
- [00:15:25.200]organic matter via dissolved organic matter
- [00:15:28.410]that shows you that you have accumulation of organic matter
- [00:15:31.830]that's microbial processed
- [00:15:33.270]or it's being microbial processed in this deeper subsoils.
- [00:15:38.820]And then we looked a little bit about,
- [00:15:42.037]that's a carbon use efficiency that goes down.
- [00:15:45.150]So that is an ratio between carbon dioxide emitted
- [00:15:49.620]and soil organic carbon and carbon dioxide emitted
- [00:15:52.890]and relative to biomass, microbial biomass carbon.
- [00:15:57.930]And that goes up.
- [00:15:59.580]If you go down, so that are topsoil, subsoil,
- [00:16:03.120]five sites, four sites and two sites.
- [00:16:06.660]And that is in a trend we see, right?
- [00:16:09.090]That is carbon use efficiency gets worse.
- [00:16:13.778]So we are emitting more CO2 per carbon dioxide
- [00:16:16.724]per SOC and per Cmic
- [00:16:18.840]if you go down with the soil depth.
- [00:16:22.020]And for the tertiary sand that means topsoil,
- [00:16:25.168]heavy fraction mineral associated 9% of organic carbon,
- [00:16:30.677]0.4% of SOC was respired,
- [00:16:34.010]third subsoil organic carbon was 99%.
- [00:16:37.980]So heavy fraction was 99%
- [00:16:40.950]mineral associated in this subsoil horizon.
- [00:16:43.650]But 2% got respired, right?
- [00:16:46.380]So you have an increase
- [00:16:47.520]in mineral associated stabilized organic matter,
- [00:16:49.913]but you have an higher percentage of carbon
- [00:16:53.160]that's getting decomposed.
- [00:16:55.050]And that is kind of counterintuitive, right?
- [00:16:59.160]So either heavy fraction is
- [00:17:04.710]less mineral protected than expected
- [00:17:07.170]or heavy fracture mineral protection is generally
- [00:17:10.350]less efficient as expected.
- [00:17:12.180]But organic carbon heavy fraction is less used
- [00:17:15.390]for metabolic activity in the topsoil than in the subsoil
- [00:17:18.540]because they have other sources
- [00:17:20.610]or microorganisms in the subsoil active,
- [00:17:24.000]but lower substrate use efficiency,
- [00:17:26.880]more decomposition needed
- [00:17:28.080]to maintain biomass mining for nutrients.
- [00:17:32.580]That was weird.
- [00:17:33.660]So going deeper, yeah.
- [00:17:38.970]So since maybe a little bit
- [00:17:40.530]of a critical comment, but I just,
- [00:17:44.118](audience member speaks indistinctly)
- [00:18:15.593]We did, they did CO2 analyze it in in situ as well.
- [00:18:18.930]But that is much more complicated
- [00:18:20.310]because you need to build this giant columns,
- [00:18:25.320]what we've seen in this soil.
- [00:18:27.570]So oxygen is no limiting factor for carbon dioxide.
- [00:18:31.530]The most limiting factor was nutrient availability.
- [00:18:35.100]And so, and resource so
- [00:18:38.190]that you get disconnected from your resources.
- [00:18:40.320]So water temperature, pH, carbon dioxide,
- [00:18:44.250]it didn't matter for the soils.
- [00:18:45.990]So we treated all soils the same, right?
- [00:18:48.630]So there is a bias if you put it just in the lab,
- [00:18:52.410]take it out of their environment.
- [00:18:55.380]But that was okay.
- [00:18:57.240]So, and because we did this,
- [00:19:00.450]the mean values over different sites,
- [00:19:02.730]we were pretty confident that this trend is real, right?
- [00:19:06.720]So that were true field reps.
- [00:19:09.030]So different sites,
- [00:19:11.640]different pedogenetic materials.
- [00:19:13.590]So that was all different, right?
- [00:19:17.010]Yeah, all right, so subsoil projects in Nebraska.
- [00:19:21.570]So here we went from three, 24 to 37 meters.
- [00:19:25.673]One project was storage and persistence of organic carbon
- [00:19:30.150]in three meter soil depth insights from 22 arable
- [00:19:33.240]and native prairie sites in Nebraska.
- [00:19:35.910]Second one was conversion of grassland to coniferous forest
- [00:19:39.420]and its impact on soil organic carbon stocks
- [00:19:41.760]on turnover on highly sandy soils,
- [00:19:44.790]and evaluation of organic carbon
- [00:19:47.157]and nitrogen dynamics in the vadose zone.
- [00:19:49.320]So, so here we went a bit crazy.
- [00:19:51.060]So we caught down to 24/37 meters, okay?
- [00:19:56.100]Starting with the first one.
- [00:19:57.870]So that is the storage and persistence
- [00:20:02.910]depending on land use.
- [00:20:04.620]So we compared native prairie sites with herbicides.
- [00:20:09.120]So that is a nine mile prairie sites
- [00:20:11.490]managed by the Center for Grassland Studies.
- [00:20:13.980]There's also a nice teaching source bit
- [00:20:16.410]and that one is in detail discussed by Chris.
- [00:20:22.140]Chris that is one part of his PhD thesis.
- [00:20:26.910]So I will not take away his some note today, right?
- [00:20:29.910]So if you are interested in this project
- [00:20:32.430]and in all the details and the fascinating data,
- [00:20:35.160]you need to show up to Chris' "Defense",
- [00:20:37.290]which is on April 23rd.
- [00:20:39.840]I will just give you,
- [00:20:41.490]you know, some lure, right?
- [00:20:43.590]So that you are coming actually.
- [00:20:45.844]So what Chris did,
- [00:20:47.730]and of course he had a lot of help,
- [00:20:49.620]but he led this project, right?
- [00:20:51.840]So that is part of his theses.
- [00:20:54.540]He was leading the project.
- [00:20:56.550]And so what Chris did was coring, right?
- [00:21:02.970]Down to three meters, 20 sites, 22 sites.
- [00:21:07.800]Each core was analyzed for the pathogenic horizons
- [00:21:10.860]and then accordingly sampled
- [00:21:12.630]for each site, course had three cores.
- [00:21:16.530]And this are the sites over here.
- [00:21:18.690]So here is the combination
- [00:21:21.750]of the different native prairie sites
- [00:21:24.060]and the arable sites.
- [00:21:26.970]And what Chris did was analyzing
- [00:21:29.640]the bulk density, pH and texture,
- [00:21:32.250]analyze the texture,
- [00:21:34.680]the exchangeable cation and iron, minimal sites,
- [00:21:39.030]carbon and nitrogen,
- [00:21:40.080]but also looked into isotopes 14C and delta 13C,
- [00:21:43.920]which gives you pretty cool information
- [00:21:45.840]about age turnover and exchange dynamics.
- [00:21:51.300]And he also analyzed microbial community structure
- [00:21:54.420]and he analyzed the samples
- [00:21:58.920]also in fractionation that was developed in my group
- [00:22:01.980]over the last 10 years,
- [00:22:03.660]10, 20 years and looked into organic carbon
- [00:22:06.690]dissolved organic matter.
- [00:22:08.760]That's the same, I'm sorry.
- [00:22:09.660]So what I extract organic matter
- [00:22:12.000]aggregate occluded organic matter
- [00:22:14.910]free organic matter.
- [00:22:18.330]So organic particles free
- [00:22:20.010]and aggregate occluded add mineral associated organic bed.
- [00:22:23.670]And I will just show you so the data are meanwhile submitted
- [00:22:28.266]and plant and soil and to Geoderma.
- [00:22:32.370]And I will just show you two highlights.
- [00:22:34.980]So that are the carbon storage compared arable to prairie.
- [00:22:40.116]So in kilogram per meter square
- [00:22:43.410]in different depth increments.
- [00:22:44.970]So we did both horizons and depth increments
- [00:22:47.940]and as Chris find out that carbon storage
- [00:22:50.850]mainly affected zero to 50 centimeters.
- [00:22:53.730]So if you switch from arable to grassland or back,
- [00:22:58.050]your carbon if a quantity wise is mostly tied
- [00:23:03.750]to the uppermost 50 centimeters.
- [00:23:06.600]What really impressive is that this is driven
- [00:23:09.720]by the mineral associated organic matter.
- [00:23:11.670]So that is water extractable,
- [00:23:13.470]that is free particulate organic matter
- [00:23:16.260]that is aggregate occluded organic matter.
- [00:23:19.650]But the biggest difference is quantitative.
- [00:23:22.050]That is most important, about 50% of soil organic carbon.
- [00:23:25.557]And we have a 40% difference.
- [00:23:27.990]So this mineral associated organic matter is
- [00:23:30.630]ambivalent, right?
- [00:23:32.010]It's stabilize organic matter, but it's also sensitive
- [00:23:35.850]and this ambivalent nature that is driving the resilience
- [00:23:39.960]of soils against carbon depletion
- [00:23:42.660]and land use change derived disturbances, right?
- [00:23:47.040]So that is so far, there's a lot of discussion
- [00:23:50.100]about this mineral associated organic matter,
- [00:23:51.870]but our research clearly shows
- [00:23:54.210]that is in part highly stabilized,
- [00:23:56.160]but it is in part also sensitive to disturbances, right?
- [00:23:59.820]And that is the most important fraction over here.
- [00:24:02.310]So again, please show up on April 23rd,
- [00:24:07.710]Chris will explain all the details
- [00:24:10.710]you need for this project.
- [00:24:13.890]So there was a project together
- [00:24:15.570]with the group from Dr. Drijber
- [00:24:17.997]and the group from Dr. Awada led by Lidong Li.
- [00:24:23.790]She was a postdoc in my lab,
- [00:24:25.710]meanwhile working for Colorado State University.
- [00:24:30.090]And here we looked into the consequences
- [00:24:31.830]of conversion of grassland to coniferous forest
- [00:24:35.310]for topsoil and subsoil carbon dynamics,
- [00:24:39.960]meanwhile published in two studies, plant and soil
- [00:24:43.890]and environmental modeling and assessment.
- [00:24:47.130]And the background is that if you look over here,
- [00:24:54.270]the primary drivers of grassland loss
- [00:24:57.240]and grassland, rangeland, that is a backbone
- [00:25:01.050]of the US cattle production, right?
- [00:25:04.200]Or one of the backbones.
- [00:25:05.850]And grasslands and rangelands store a lot of carbon, right?
- [00:25:11.490]So losing this kind of ecosystems
- [00:25:14.970]does have a lot of negative consequences.
- [00:25:17.820]Not only biogeochemically but also agriculturally
- [00:25:23.730]or from a ag business standpoint, right?
- [00:25:26.730]So, and the biggest threat to grasslands is
- [00:25:30.180]land use conversion.
- [00:25:31.200]So putting grassland under tillage and growing row crops
- [00:25:35.040]or tree cover expansion, that's a red cedar, right?
- [00:25:39.150]So this is resource led by Derek Weitzel
- [00:25:44.630]here at UNL and together with NRCS.
- [00:25:48.510]So they developed this maps
- [00:25:50.460]and showing over here the woodland
- [00:25:54.120]or red cedar expansion from 1990 to 2020
- [00:25:59.010]for the Great Plains, right?
- [00:26:00.390]So that is one of the biggest threats
- [00:26:02.340]of grasslands in the Great Plains.
- [00:26:07.470]So this how it looks,
- [00:26:09.480]that's a woodland expansion, right?
- [00:26:11.460]And that also threatens the central grassland of Nebraska
- [00:26:16.590]and that is a unique ecosystem, right?
- [00:26:20.100]So Ca. 14 million acres,
- [00:26:21.900]one of the most intact prairie ecoregions in the world.
- [00:26:25.830]So direct published a lot of stuff
- [00:26:28.950]with this group and this collaborators
- [00:26:31.597]about this red cedar encroachment,
- [00:26:35.130]but also about this Sandhill ecosystem.
- [00:26:40.080]And this is the largest stabilized sand dune formation
- [00:26:43.080]in the western hemisphere, okay?
- [00:26:45.867]And if you look at a global meta study
- [00:26:49.920]that clearly shows if you go
- [00:26:51.780]from temperate grassland and shrublands
- [00:26:54.300]to temperate forest,
- [00:26:56.790]you are losing about 50% of your crop, right?
- [00:27:01.230]You are having year 100 tons
- [00:27:06.660]and this is 300 tons, right?
- [00:27:08.610]So three times more in soil under tempered grasslands
- [00:27:12.360]and under tempered forests.
- [00:27:14.250]So if you would change the entire grassland
- [00:27:17.640]in the Great Plains, including the centers,
- [00:27:22.200]you are losing more about 50%
- [00:27:24.990]of your carbon stored in this ecosystem, right?
- [00:27:27.267]And that is huge, that's a huge number.
- [00:27:30.150]So large uncertainties remain in understanding
- [00:27:34.620]of how woody grassland encroachment affects
- [00:27:37.140]soil organic carbon storage and persistence
- [00:27:39.180]beyond the topsoil and understanding
- [00:27:41.760]drivers of subsoil carbon dynamics
- [00:27:44.040]in different land use systems is key
- [00:27:45.990]for outlining management conservation
- [00:27:48.000]and reclamation strategies.
- [00:27:50.340]Objectives, we wanted to quantify the carbon storage
- [00:27:53.730]in study site in the Sandhills.
- [00:27:58.230]We wanted to look into turnover dynamics
- [00:28:00.690]and we wanted to clarify differences in microbial biomass
- [00:28:03.990]and community in relation to vegetation and soil depth.
- [00:28:09.030]So that where the study sites over here,
- [00:28:11.100]Nebraska National Forest at Halsey.
- [00:28:14.580]So here we have,
- [00:28:16.650]so that's a natural grassland site
- [00:28:19.020]and that are for 24 sites, we look.
- [00:28:24.420]We again did the coring zero to three meters.
- [00:28:29.040]And the land use was, we had one red cedar side,
- [00:28:33.420]one ponderosa pine side and one native crescent side.
- [00:28:36.990]The fourth stent age was 65 years
- [00:28:40.593]and 82 years for cedar and pine.
- [00:28:43.410]And we took three transects per land use
- [00:28:47.160]and four soil cores per transect.
- [00:28:49.410]So that we are 12 pseudo replicates per land use, right?
- [00:28:54.540]But kind of independence.
- [00:28:55.830]So where we are no mixing between cores.
- [00:28:58.260]So the cores where the pseudo replicates, right?
- [00:29:01.736]Then we looked into the soil.
- [00:29:02.657]So the soil is unique, it's more than 93% sand, right?
- [00:29:06.450]So almost no clay and silt.
- [00:29:08.580]And then we looked
- [00:29:09.413]into stocks delta 13C mean residence time
- [00:29:12.480]and used fame analyzers
- [00:29:14.550]to look into microbial biomass and community structure.
- [00:29:19.500]Okay, what did we find out?
- [00:29:20.940]So here we needed to look into fixed depth increments.
- [00:29:25.200]The zero to 10 is is the A-horizon.
- [00:29:28.050]Everything below 10 centimeters is C-Horizon.
- [00:29:31.500]So you don't have any horizon in this environment
- [00:29:34.800]because of this high C content, right?
- [00:29:37.080]High sand content.
- [00:29:38.730]So then we looked into the carbon stocks.
- [00:29:41.190]So interestingly, the forest ecosystem
- [00:29:45.390]only had higher carbon stocks in the topsoil,
- [00:29:49.860]zero to 10 centimeters.
- [00:29:51.930]If you go below, you see that the grassland soil
- [00:29:57.300]that is still not significant,
- [00:29:59.760]but especially in this depth 100 to 170
- [00:30:03.000]and 170, 240,
- [00:30:05.610]we see a significant increase
- [00:30:08.340]of carbon storage under the grassland.
- [00:30:10.500]So the forest changed the carbon storage only in the topsoil
- [00:30:15.380]in the uppermost 10 centimeters.
- [00:30:18.300]And this does have consequences
- [00:30:19.950]for the overall storage, right?
- [00:30:22.950]So zero to 300,
- [00:30:26.806]that is ceder 6.8, pine 5.8.
- [00:30:31.800]And we have the grassland,
- [00:30:32.880]a significant higher carbon storage.
- [00:30:35.700]If you look in the zero to three meters,
- [00:30:37.770]and this has implications, right?
- [00:30:39.780]If you go out and sample this for 30 centimeters,
- [00:30:43.350]you get a completely different story
- [00:30:45.240]about the carbon storage
- [00:30:46.560]and the carbon response to this land use change
- [00:30:49.500]as you would do if you go three meters deep, right?
- [00:30:52.770]So that has implications.
- [00:30:54.600]If someone says, okay, I have a study
- [00:30:57.240]and we've seen carbons is carbon storage is increasing
- [00:31:01.800]by planting forest, right?
- [00:31:04.350]That's only valid for 10 centimeters.
- [00:31:06.240]If you go all the way down to three meters,
- [00:31:08.310]you see the opposite is the case,
- [00:31:09.690]you are losing carbon, right?
- [00:31:11.940]And that is if you look here, 30 to 300 centimeters,
- [00:31:17.640]3.8, 3.5, 5.2, right?
- [00:31:20.310]So here is the main difference, okay?
- [00:31:23.850]And then we looked into the mean residence time,
- [00:31:26.400]here we had,
- [00:31:27.750]so grassland data have a different data,
- [00:31:30.480]13C value than the forest.
- [00:31:32.340]And based on the changes in data 13C,
- [00:31:34.830]you can calculate or roughly estimates mean residence time.
- [00:31:38.760]So not really surprising,
- [00:31:40.830]we see a higher mean residence time in the topsoil
- [00:31:44.430]compared to the subsoil.
- [00:31:46.140]Interestingly the subsoil mean residence time
- [00:31:49.710]between 10 centimeters and 300 is not different.
- [00:31:53.510]Here is the same.
- [00:31:54.343]So we have a lot of variability,
- [00:31:55.650]but basically the carbon turns
- [00:31:57.450]over independent from depth at the same speed
- [00:32:00.750]and that means the resources are homogeneously distributed
- [00:32:04.890]down to three meters.
- [00:32:06.690]So resources, pH, water, nutrients,
- [00:32:10.500]everything microbes need to decompose organic matter.
- [00:32:14.040]And we don't have gradients in clay,
- [00:32:17.190]we don't have gradients in iron oxides.
- [00:32:20.040]So the resource supply is homogeneous in this ecosystems.
- [00:32:25.800]And that means that you have approximately
- [00:32:27.900]the same mean residence time
- [00:32:29.610]for across 10 centimeters to 300 centimeters.
- [00:32:35.370]What a little bit is different is that pine carbon
- [00:32:38.370]turns over a little bit quicker than in average than cedar.
- [00:32:44.370]So that is the biggest difference vegetation wise,
- [00:32:47.850]that here is a little bit faster than here
- [00:32:52.530]for whatever reasons.
- [00:32:53.610]So that can have tons of reasons
- [00:32:56.250]because carbon decomposition is not mainly driven
- [00:32:59.610]by organic matter composition, right?
- [00:33:01.913]This is about the decomposition environment.
- [00:33:05.580]So how are the conditions,
- [00:33:07.170]how well are the conditions for microorganisms to decompose?
- [00:33:11.520]The question is always why are microorganisms
- [00:33:14.970]not decomposing?
- [00:33:16.050]What holds them back?
- [00:33:17.580]Because decomposition of organic matter to CO2 is
- [00:33:20.730]thermodynamically favored.
- [00:33:22.680]So if this is not interrupted, it would go to CO2,
- [00:33:26.280]but at some point the activation energy
- [00:33:29.160]or the conditions are so bad
- [00:33:30.870]that microorganisms do not decompose.
- [00:33:33.900]Best example is permafrost soil, right?
- [00:33:36.960]As long as this stuff is frozen, you don't see CO2.
- [00:33:40.020]As soon as this melts,
- [00:33:42.360]you see methane, CO2 through the roof, right?
- [00:33:46.260]And that is not about
- [00:33:47.520]the organic matter and it's composition.
- [00:33:51.270]It's about city composition conditions, right?
- [00:33:53.940]As soon it gets melted, ice is away, the water's away,
- [00:33:57.750]microbes take over.
- [00:33:58.770]They don't care how the composition is, right?
- [00:34:02.430]And so then we looked a little bit more in detail
- [00:34:06.420]what might be the reasons?
- [00:34:07.830]And was Dr. Drijber together we looked into bacteria biomass
- [00:34:13.980]and that was strikingly
- [00:34:15.720]that we see in the subsoil an increase
- [00:34:19.320]in microbial biomass carbon, right?
- [00:34:21.957]So, and that could drive the entire petal
- [00:34:25.110]and microbial biomass carbon.
- [00:34:27.390]Meanwhile it's assumed to contribute at least 50%
- [00:34:31.110]to soil organic carbon
- [00:34:32.220]because microbial biomass is if microbes die off,
- [00:34:36.630]they're either getting,
- [00:34:37.590]rather getting decomposed
- [00:34:38.910]or the stuff is stabilized.
- [00:34:40.950]But usually especially fungus,
- [00:34:44.280]but mainly bacteria are close to mineral surfaces.
- [00:34:47.430]So if they die off the envelopes,
- [00:34:49.890]the sellable material is already attached
- [00:34:51.990]to mineral surfaces, which is an excellent
- [00:34:55.260]stabilization mechanism.
- [00:34:56.790]It's also highly reactive, this stuff, right?
- [00:34:59.520]So it can really provide micro-aggregation cores.
- [00:35:04.230]So microbial biomass is contributing largely
- [00:35:07.290]to our soil organic carbon storage.
- [00:35:10.950]And there we are actually two meta studies
- [00:35:14.820]looking into the contribution
- [00:35:16.290]of microbial-derived carbon to (indistinct) carbon
- [00:35:19.740]and subdivided into agriculture grassland and forest.
- [00:35:23.067]And what you see compared grassland
- [00:35:25.920]to forest is in higher contribution
- [00:35:28.320]of microbial derived carbon to the overall carbon, right?
- [00:35:32.730]That was shown here and it was shown here as well.
- [00:35:34.980]So that's the same story, 35%, 47%.
- [00:35:39.270]So the contribution of soil organic,
- [00:35:42.150]microbial derived carbon,
- [00:35:44.580]choose overall carbon is in grassland higher than in forest.
- [00:35:48.210]And this is what we see over here,
- [00:35:50.190]what we think might drive this stuff, right?
- [00:35:53.610]Okay, take home messages.
- [00:35:56.340]Conversion of native grassland to seed or pine forest
- [00:35:59.580]increase soil organic farm stock and topsoil,
- [00:36:01.920]but decreased SOC stock and subsoil.
- [00:36:05.430]Total SOC stock bigger on grassland than in forest.
- [00:36:10.230]57 to 70% is stored in 30 to 300 centimeters.
- [00:36:16.710]And the decrease in SOC storage was associated
- [00:36:19.590]with reduced microbial biomass
- [00:36:21.510]and altered microbial community structure
- [00:36:23.550]on a forest relative to grassland.
- [00:36:26.544]And with the decrease in microbial biomass on the forest
- [00:36:29.250]might be mediated by declines
- [00:36:31.140]in soil moisture, pH and nutrient.
- [00:36:34.140]That is still not clear, right?
- [00:36:37.740]So that is still needs to have closer attention.
- [00:36:44.280]Okay, last one.
- [00:36:46.440]Evaluation of carbon and nitrogen dynamics
- [00:36:48.810]in the vadose zone.
- [00:36:50.310]That was a study with a group of Dr. Snow
- [00:36:55.650]and Dr. Malakar from SNR,
- [00:36:59.370]John Shields were the grad students who led the student
- [00:37:02.790]who led the sampling and coring
- [00:37:06.060]and his master thesis.
- [00:37:08.610]And Lidong published or was leading the paper
- [00:37:12.810]that was published
- [00:37:13.710]in "Science of the Total Environment" last year.
- [00:37:18.390]So what we did here was there were two sides, right?
- [00:37:22.410]And they were sampled down to 24 meters
- [00:37:24.930]and down to 37 meters.
- [00:37:28.440]And then we had this depth profiles.
- [00:37:30.960]So we measured nitrate, pure water nitrate,
- [00:37:34.830]ammonium, nitrogen, total nitrogen, delta 13C,
- [00:37:39.210]extractable organic carbon, total organic carbon,
- [00:37:42.870]pH and water filled pore space.
- [00:37:45.930]So what you see over here is that zero meters, right?
- [00:37:50.550]Five meter, 10 meter, 50 meters, 20 meters,
- [00:37:54.180]that is 12 meters deep.
- [00:37:56.760]All of a sudden you see a peak, right?
- [00:38:00.990]All of a sudden all these values are going up.
- [00:38:03.780]If you look at the soil organic carbon,
- [00:38:06.000]that is about six milligram per gram, right?
- [00:38:11.520]So six gram per kilogram,
- [00:38:14.880]the nitrate and nitrogen cycle is going up, all right?
- [00:38:19.380]So there is some kind of decomposition going on down under.
- [00:38:22.920]If you look over here, the soil organic carbon,
- [00:38:25.860]it's about close to 60 milligram.
- [00:38:29.100]So that's 60 gram per kilogram, that is 6%.
- [00:38:32.970]12% organic matter in 12 meter deep, right?
- [00:38:37.800]And you see activity ammonium nitrogen,
- [00:38:40.890]ammonium goes up,
- [00:38:42.300]total nitrogen goes up.
- [00:38:43.950]So there is some kind of decomposition party
- [00:38:48.330]going down deep, right?
- [00:38:50.910]The question is who invited?
- [00:38:54.090]who are the guests?
- [00:38:56.190]What's for dinner and how is transportation, right?
- [00:39:00.330]So our assumption is that these are buried A-horizons.
- [00:39:04.920]So A-horizons, some kind
- [00:39:07.020]of buried erosion event or whatever.
- [00:39:10.530]And this is still down there.
- [00:39:13.320]So that is cycling, it's being processed, right?
- [00:39:16.500]We don't know how much and and so on, right?
- [00:39:19.407]So, but it is down there, right?
- [00:39:21.030]So the data are convincing.
- [00:39:26.280]So, and if you look,
- [00:39:28.260]if you look at the depth intervals,
- [00:39:30.300]three meter three to 10,
- [00:39:31.440]10 to 20, 20 to 24 and zero to 24.
- [00:39:36.660]So that is the percentage you have
- [00:39:40.920]in 20 to 24 meters is 2%,
- [00:39:44.490]13% and two to 20 meters,
- [00:39:47.550]and then three 16% in zero to 10 meters
- [00:39:52.110]and only 20% in the uppermost three 30 meters
- [00:39:55.200]if you go down that deep, right?
- [00:39:57.600]So that is changing the perspective entirely.
- [00:40:00.840]And then here, same.
- [00:40:02.700]Because of this,
- [00:40:05.844]some of our core authors made a joke,
- [00:40:08.760]so we maybe hit a desk mammoth or something right?
- [00:40:12.780]Down there, because you see that is 80%
- [00:40:18.930]of the carbon in this entire 37 meter is
- [00:40:23.070]in 10 to 20 meters because of this A-horizon, right?
- [00:40:27.030]So that is changing our perspective and our analytics
- [00:40:30.390]and understanding how much carbon actually
- [00:40:32.430]can be down there completely.
- [00:40:35.010]But that was published in 2023, right?
- [00:40:39.300]That was a paper published in 2013.
- [00:40:42.600]So they sampled Harper and Tibbett,
- [00:40:46.110]2013 published in "Plant and Soil",
- [00:40:48.420]mean depth, 22, 12, 27, 20, 27, 21.
- [00:40:54.867]And that was a percentage they found in zero to five meters,
- [00:40:59.027]13, 16, 13, 20.
- [00:41:00.540]So more than 80% below five meters, right?
- [00:41:04.980]And they concluded, "The paper demonstrates the need
- [00:41:08.340]for reassessment of secure and arbitrary
- [00:41:10.890]shallow soil dumpling depths
- [00:41:12.930]for assessing carbon stocks.
- [00:41:14.460]A revision of global SOC estimates
- [00:41:18.090]and elucidation of the composition and fate of deep carbon
- [00:41:21.450]in response to land use and climate change."
- [00:41:25.950]And we agree.
- [00:41:29.250]Thank you for coming and I'm happy to take questions.
- [00:41:36.210]Thank you very much for that great presentation.
- [00:41:39.060]If you have a question, please wait for the microphone
- [00:41:41.160]so that folks online can hear you.
- [00:41:42.750]Any questions?
- [00:41:44.970]All right. Thank you Dr. Kaiser
- [00:41:49.710]for this great presentation.
- [00:41:51.660]I have just a curious question.
- [00:41:54.480]We have been hearing like China and the Middle East country,
- [00:41:58.710]they're trying to expand the vegetated area
- [00:42:01.770]in the desert condition.
- [00:42:04.110]So like if we are shifting from bare land to vegetated,
- [00:42:10.440]then both grassland and forest can work.
- [00:42:14.010]But from the study you have done here,
- [00:42:16.710]so what would you suggest whether it'll be better switching
- [00:42:20.790]to grassland or forest in those area in terms of adaptation
- [00:42:26.550]and then mitigating climate change?
- [00:42:30.263]So the question would be you have like desert bare land
- [00:42:36.660]and then you would,
- [00:42:37.980]then you would transform it
- [00:42:39.090]either to grassland or forest.
- [00:42:42.370]From a carbon perspective, grassland.
- [00:42:45.630]So based on the stuff we know
- [00:42:47.280]grassland stores more than forest.
- [00:42:50.610]Especially if you go deep, right?
- [00:42:52.590]But if you start, like let's say,
- [00:42:55.050]you really start with a desert soil
- [00:42:57.480]and you grow any kind of crop,
- [00:43:00.000]you have an higher input of organic matter,
- [00:43:02.700]the stuff you need is water, right?
- [00:43:04.980]So that is a biggest issue.
- [00:43:07.230]So if you transfer a desert into kind of a vegetated area,
- [00:43:14.850]you always increase your carbon storage
- [00:43:16.920]because growing plants roots,
- [00:43:18.690]everything is bringing input, right?
- [00:43:24.999]From a soil carbon perspective,
- [00:43:26.490]based on what I know and the publication,
- [00:43:28.770]I know the soil carbon storage
- [00:43:32.190]under grassland is usually higher as under forest,
- [00:43:35.280]especially if you are leaving the topsoil.
- [00:43:42.600]You talked about the microbes in the subsoil
- [00:43:48.403]being limited, not doing their work or something like this.
- [00:43:52.830]What are the chances that it might be nitrogen limited
- [00:43:55.680]or oxygen limited?
- [00:43:58.020]Nitrogen limited, yes.
- [00:44:00.030]What I know about oxygen limitation, no.
- [00:44:03.167]What I was pointing out is that
- [00:44:09.120]usually in the subsoil you have less nutrients,
- [00:44:14.400]less substrate and you have a pretty good chance
- [00:44:17.130]that the microbes are sitting on a spot
- [00:44:19.920]where they don't get water and nutrients.
- [00:44:21.630]So we have a disconnection between decomposer and substrate
- [00:44:25.620]because more than 90% of bacteria are lazy.
- [00:44:29.190]They're hanging around in their pores and waiting for food.
- [00:44:32.460]If the food is driving next block down,
- [00:44:35.700]they don't get the food.
- [00:44:37.440]Fungi are better adapted, they grow,
- [00:44:39.720]but they are usually in more abundant,
- [00:44:43.470]I think at least in the four topsoils, right?
- [00:44:47.040]But down as soon as what research shows is,
- [00:44:50.460]as soon as you have enough nutrients and water,
- [00:44:53.310]they are able to decode those.
- [00:44:55.860]So it it's basically a substrate limitation
- [00:44:58.350]and nutrient limitation
- [00:44:59.340]and a disconnection between resources and microorganisms.
- [00:45:09.119]Thank you for great presentation.
- [00:45:11.490]Just a quick question.
- [00:45:12.780]Those forests that you mentioned, those were man planted,
- [00:45:16.230]those were not native, right?
- [00:45:18.060]Yes. And that's when you can
- [00:45:20.147]apply number of years since
- [00:45:21.060]they were established and so forth.
- [00:45:23.401]Yeah. And so that's different
- [00:45:24.660]than if it was native forest at this point, right?
- [00:45:30.210]On a native forest, you wouldn't know
- [00:45:33.840]number of years it's been in place.
- [00:45:37.923]So you mean the duration of...
- [00:45:41.220]Right, right.
- [00:45:42.270]Yeah, so I mean what we looked was a little bit
- [00:45:45.510]like in the end member of encroachment, right?
- [00:45:48.540]So if you have an encroachment,
- [00:45:51.000]you have a red seed of forest
- [00:45:53.160]and that was a red seed of forest and a pine forest.
- [00:45:55.680]But it was planted 65, 80 years ago
- [00:45:58.980]to have at some point this information
- [00:46:01.410]what happens to your ecosystem if encroachment,
- [00:46:07.440]if you forest some stuff and so on.
- [00:46:10.350]So that was one of the reasons why they did this, yeah.
- [00:46:15.930]Thanks (indistinct).
- [00:46:20.580]So with the differences that you saw
- [00:46:23.160]between the grasslands and the forest?
- [00:46:26.250]And what are your thoughts about, you know,
- [00:46:29.430]the differences in the plant inputs
- [00:46:32.190]or plant root biomass?
- [00:46:36.090]Do you think that played a role at all
- [00:46:38.550]in the differences in carbon that you see?
- [00:46:41.670]For sure, yeah.
- [00:46:42.720]So what we know from other side,
- [00:46:45.750]so we didn't measure root biomass
- [00:46:47.700]because that's a pain, it takes forever
- [00:46:50.700]and you never know if this is a dead route
- [00:46:52.950]or a living route or whatever.
- [00:46:56.280]So what we see also with Chris' project,
- [00:47:00.450]so we see roots grassroots down to three, four meters.
- [00:47:05.430]So the rooting depth for grassland is deeper
- [00:47:08.418]than for forests, yeah.
- [00:47:10.170]So the main input in forest is topsoil, right?
- [00:47:14.610]And then, you know, you need to look,
- [00:47:17.400]it's also what kind of micro-pores do we have?
- [00:47:20.220]How much dissolved organic matter goes down, right?
- [00:47:23.041]So it's really a biogeochemical question, right?
- [00:47:29.790]But the root input is different between forest and grassland
- [00:47:33.210]and that does have an effect, that's for sure.
- [00:47:36.300]So I probably should know the answer to this,
- [00:47:38.353]but is has it been shown
- [00:47:39.810]that there's big differences in microbial diversity
- [00:47:43.470]between grasslands and forest?
- [00:47:48.030]I don't know.
- [00:47:51.570]So I didn't do,
- [00:47:54.030]I mean we did the fame analyzers, right?
- [00:47:55.860]So that gave us a little bit of information,
- [00:47:58.950]so that changed a bit.
- [00:48:00.951]But based on the literature, what I know it should be.
- [00:48:04.980]I mean, you have different,
- [00:48:06.600]you have different nutrient composition
- [00:48:12.810]in your material, right?
- [00:48:14.787]And you have a bit more lignin in your forest material.
- [00:48:19.650]So the decomposer community should be adapted.
- [00:48:22.560]So I'm pretty sure I don't have own data,
- [00:48:25.230]but I'm pretty sure that there are differences
- [00:48:28.200]in community structure and diversity, yeah.
- [00:48:38.760]Good presentation.
- [00:48:40.080]A quick question,
- [00:48:40.980]this kind of relates to the carbon markets.
- [00:48:43.380]So in your estimation,
- [00:48:45.660]if we have an irrigated system versus a rain-fed system
- [00:48:49.260]in like say in Nebraska,
- [00:48:51.540]do you think there's a potential
- [00:48:53.550]for a higher carbon loss at soil surface depth
- [00:48:56.850]than an irrigated system, than a rain-fed system?
- [00:48:59.670]And then the second question is related to models.
- [00:49:01.920]Most models are only modeling down to 10 centimeters
- [00:49:05.430]at most, maybe 30 centimeters.
- [00:49:07.110]And so a lot of our policy is judged
- [00:49:09.180]on those modeling aspects of what works and what doesn't.
- [00:49:13.680]So is there, should we look,
- [00:49:14.910]start evaluating either a different approach
- [00:49:17.250]or start looking at models
- [00:49:18.630]that can start capturing these changes over at depth?
- [00:49:23.130]The second question, yes, without any doubt.
- [00:49:26.820]So the models need to capture the subsoil carbon dynamics
- [00:49:30.540]because you're missing a big part, right?
- [00:49:32.910]So what we see ortho in other studies that
- [00:49:35.160]the main effects are in the uppermost 50 centimeters.
- [00:49:38.280]So you should at least consider this, right?
- [00:49:41.310]For total terrestrial carbon budget, you need to go deeper,
- [00:49:44.580]but at at least addressing the changes
- [00:49:47.190]in the uppermost 50 centimeters,
- [00:49:49.170]because if you go in the down 30 centimeters,
- [00:49:53.790]let's say your A-horizons stops at 20 centimeters
- [00:49:57.240]and your B horizon starts
- [00:49:59.040]and you have changing in carbon in your B horizon,
- [00:50:02.040]that changes are have a long,
- [00:50:03.930]much longer term impact than in the A-horizon
- [00:50:06.810]because stabilization is,
- [00:50:08.310]and the long the mean residence time is higher, right?
- [00:50:11.730]So yes.
- [00:50:13.650]Irrigation, non-irrigation, that is complicated
- [00:50:16.650]because you need to look,
- [00:50:19.440]I mean, usually higher biomass, higher input, right?
- [00:50:23.430]If you have higher input,
- [00:50:24.540]you should see higher organic carbon contents.
- [00:50:27.390]The question is in which form?
- [00:50:28.830]If your organic carbon contents is increasing
- [00:50:31.260]as a particulate organic matter,
- [00:50:33.600]it's going away within a year or two
- [00:50:36.030]once you switch your management, right?
- [00:50:38.400]If your increase is in a mineral associated organic matter,
- [00:50:42.677]that might have an effect, right?
- [00:50:45.360]And then if you wanna use the subsoil
- [00:50:48.330]and you rely on dissolved organic matter,
- [00:50:51.060]you need to have the flow, right?
- [00:50:54.660]So it needs to travel,
- [00:50:56.010]but dissolved organic matter is usually
- [00:50:58.230]below 5% of total soil organic matter.
- [00:51:00.630]So it is quantitative wise not so important,
- [00:51:04.350]qualitative wise, it's transport of energy,
- [00:51:06.690]transport of substrate, transport of nutrients.
- [00:51:09.300]So ecological wise, it's highly important, right?
- [00:51:12.690]But so for the subsoil
- [00:51:16.350]and then you have also the, you know,
- [00:51:18.360]subsoils substrate horizons playing.
- [00:51:21.180]So that question is tough to answer
- [00:51:23.730]because you would need to compare irrigation,
- [00:51:25.860]no-irrigation, same crop rotation,
- [00:51:29.040]same fertilization, same soil type.
- [00:51:31.680]If you change this, you change the carbon dynamics
- [00:51:34.230]and you cannot really say something, right?
- [00:51:36.936]People saying they see cover crops increasing
- [00:51:42.360]subsoil carbon storage after two years.
- [00:51:46.620]I'm a little bit skeptic about this information.
- [00:51:49.740]Based on what I know,
- [00:51:51.060]the system is not reacting that fast,
- [00:51:53.040]and cover crops you need really to increase the subsoil,
- [00:51:56.580]biomass productions, the roots going down,
- [00:51:58.860]then you might have a chance.
- [00:51:59.940]But that is tough to analyze.
- [00:52:08.490]Based on some of your research here and others, how much,
- [00:52:16.890]how close are these soils to maximum storage of carbon?
- [00:52:23.160]What is the potential with, say carbon markets
- [00:52:26.670]to store more carbon in these kinds of soils?
- [00:52:30.930]Depends on the site,
- [00:52:32.130]but they are in part depleted by maximum 50%,
- [00:52:37.217]Chris, is that right?
- [00:52:38.520]Yeah, so it goes from about under saturation, 10% to 50%.
- [00:52:44.190]That's site dependent.
- [00:52:45.990]It's highly site specific.
- [00:52:47.460]So some of all comparisons between arable land
- [00:52:51.210]and native grassland do not show big differences.
- [00:52:55.050]Some of them show very big differences.
- [00:52:57.120]So it depends a little bit what you did with your soil
- [00:52:59.220]and what you have for soil.
- [00:53:00.990]So that would be kind of an, you know,
- [00:53:04.530]you would need to know.
- [00:53:06.060]That is was one of the reasons why we looked into this,
- [00:53:09.510]to identify areas where this is most efficient, right?
- [00:53:14.160]To identify soils or soil landscapes
- [00:53:17.550]where you have the biggest saturation deficit
- [00:53:20.190]because of intensifying agriculture
- [00:53:22.830]and that comes from site specific analyzers.
- [00:53:25.020]So it's not as easy to answer.
- [00:53:27.243]Kind of a follow up with that then,
- [00:53:29.760]you're sampling in like nine mile prairie in,
- [00:53:32.520]in native prairie is unused grasslands, so to speak.
- [00:53:37.680]Yeah. The vast majority
- [00:53:40.110]of native grasslands are utilized by livestock.
- [00:53:43.950]Yeah. So under a grazing scenario,
- [00:53:47.490]do you anticipate there'd be much difference
- [00:53:50.010]and what kind of a difference would you expect
- [00:53:51.780]in that carbon storage via these different depths?
- [00:53:56.910]That's a good question.
- [00:53:57.780]I'm pretty sure that there are meta studies
- [00:54:00.900]and studies about this,
- [00:54:02.100]so right from the top of my head.
- [00:54:04.350]So there are also studies going on at UNL
- [00:54:09.150]looking at effect of trampling, getting carbon in
- [00:54:13.920]and probably depends a little bit of
- [00:54:18.720]if you fertilize your grasslands and increase your biomass.
- [00:54:22.320]And what I would not expect is a reduction,
- [00:54:29.040]so I cannot tell you,
- [00:54:33.060]but what I would not expect is
- [00:54:34.800]by using a native grassland and a rangeland
- [00:54:38.850]that you see this big drop in carbon
- [00:54:43.200]that you would see if you put it under till, right?
- [00:54:47.160]But the other ones,
- [00:54:49.363]so I don't have any meta study in mind that could answer,
- [00:54:55.470]but there are for sure meta studies I would showing
- [00:54:58.020]the difference between native grassland and rangeland.
- [00:55:02.610]So I'm not sure, but my first guess would
- [00:55:05.460]you see a decrease.
- [00:55:07.080]But how much, I don't know.
- [00:55:09.840]All right, we have a question from our online audience
- [00:55:12.600]from Mike McDonald.
- [00:55:14.220]It says, Michael, in light of your last slide and summary,
- [00:55:17.460]discuss how your biochar truly impacts the deeper subsoil,
- [00:55:21.360]so organic matter or not?
- [00:55:25.020]It depends how deep you bury it,
- [00:55:28.410]but the nice thing about biochar is
- [00:55:31.350]you don't need to bury it deep.
- [00:55:33.510]You can put it in the first 20 or 30 centimeters
- [00:55:36.510]or 10 centimeters and you will have a storage
- [00:55:38.670]for the next decades to centuries.
- [00:55:42.540]So biochar is this charcoal, paralyzed, organic matter
- [00:55:47.310]that is highly unattractive for microorganisms.
- [00:55:50.280]And if you bury it deep,
- [00:55:52.560]you have the perfect carbon storage.
- [00:55:54.750]But that takes, you know, deep plowing.
- [00:55:58.740]No one is doing this,
- [00:56:00.210]at least as not, I'm aware of large scale,
- [00:56:03.840]but again, biochar works
- [00:56:05.880]as good as in the topsoil as in the subsoil.
- [00:56:10.710]Follow up to it.
- [00:56:11.550]Just to go a little bit more on that, as Mike asked,
- [00:56:15.090]can you discuss your methodology
- [00:56:16.980]for the biochar site with Lincoln
- [00:56:19.500]and how it addresses the two areas
- [00:56:21.900]of stored organic matter as depicted in your reviews?
- [00:56:29.040]Okay, the question was about
- [00:56:31.830]the biochar sites at Lincoln?
- [00:56:35.070]And, okay, so our biochar work is
- [00:56:38.093]basically management oriented.
- [00:56:40.710]So we have,
- [00:56:42.240]we established in 2023,
- [00:56:44.490]one of the biggest biochar experiments in the country.
- [00:56:47.850]That's 16 acres.
- [00:56:49.620]We have four treatments, four reps, each rep is one acre.
- [00:56:53.160]So that is large scale application of biochar.
- [00:56:55.530]We apply 20 tons per hectare, which is 8.5 per acre
- [00:57:00.090]and we combined it with biosolids.
- [00:57:02.040]So Biosolid is an organic waste product
- [00:57:05.970]from the wastewater treatment
- [00:57:08.130]and that's an excellent organic fertilizer.
- [00:57:10.080]So contains nitrogen, phosphorous, water.
- [00:57:12.540]If you combine it, you can bring down the biochar
- [00:57:15.270]because it's cost very costly
- [00:57:17.910]and you get additional carbon from biosolid
- [00:57:20.100]that can be co-stabilized.
- [00:57:22.140]So here we are looking into synergistic effects
- [00:57:24.690]between biochar and biosolids
- [00:57:26.400]in this large scale field experiment.
- [00:57:28.767]And we have two other field experiment
- [00:57:31.050]where we look under irrigated and non-irrigated sites
- [00:57:34.050]where we combine biochar with cover crops.
- [00:57:36.690]Everything goes into carbon storage.
- [00:57:39.090]So how much carbon we store
- [00:57:40.680]because biochar carbon is stable for centuries.
- [00:57:45.750]But we also look into nitrate retention
- [00:57:49.770]because biochar was shown
- [00:57:51.090]to increase nitrate retention, water retention.
- [00:57:53.700]We are looking into microbial community structure.
- [00:57:56.160]We are looking into greenhouse gas emissions,
- [00:57:58.680]we are looking into yield
- [00:58:00.660]and our biomass, biochar, biosolid
- [00:58:06.060]showed this year no differences in yield
- [00:58:09.150]between mineral fertilizer and biosolid fertilizer
- [00:58:12.300]large scale, right?
- [00:58:14.160]And then, so this is about, you know,
- [00:58:16.740]combining climate smart management,
- [00:58:20.560]different climate smart management options
- [00:58:23.820]to maximize with (indistinct) effects, I'm sorry.
- [00:58:30.420]And looking really into carbon storage,
- [00:58:33.030]carbon stabilization,
- [00:58:33.990]but also into improved nutrient retention, water retention
- [00:58:37.500]and better or improve sustainable crop production.
- [00:58:41.910]So that is the other part of my research activities.
- [00:58:48.510]So deep soil, carbon and biochar
- [00:58:50.220]and that goes into this direction, all right?
- [00:58:52.950]Well thank you very much.
- [00:58:54.000]We're out of time now,
- [00:58:55.230]so let's all thank Michael Kaiser
- [00:58:57.687]for joining us today.
- [00:58:58.915](audience applauds)
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