8 - 2020 Soybean Management Field Days - Cereal Rye Influence on soil Nutrients and Microbial Abundance
Cereal Rye Influence on soil Nutrients and Microbial Abundance - Katja Koehler-Cole, UNL Research Assistant Professor. This presentation includes: What groups of microbes are at work in our soils?; How can we use cover crops to improve the abundance of soil microbes?; How do cover crops influence soil nutrients?; and What does this mean for the health of our soils?
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[00:00:06.920]My name is Katja Koehler-Cole
[00:00:08.500]I'm a research assistant professor
[00:00:10.140]in the department of Agronomy and Horticulture at UNL.
[00:00:13.690]So my talk today is going to be on a project that we had
[00:00:17.180]where we looked at cereal rye and how it influences
[00:00:20.470]soil nutrients and microbial abundance, before soybean.
[00:00:27.440]So this is basically a project on soil health,
[00:00:30.580]and we are focusing on one indicator of soil health
[00:00:33.010]which is the microbial communities
[00:00:35.280]microbial abundance and diversity.
[00:00:37.860]We know that in soybean systems we have some challenges.
[00:00:42.650]We are facing a loss of nutrients especially nitrate,
[00:00:47.140]and the period where we actually lose the most soy nitrate,
[00:00:51.300]in a corn soybean rotation is the period
[00:00:53.320]before planting soybeans
[00:00:55.430]because the soil warms up microbes,
[00:00:58.540]decomposed organic matter
[00:01:00.150]and then there are no plants there
[00:01:01.630]to take up the nitrogen that's released.
[00:01:03.530]So there is potentially quite a bit of nitrogen loss.
[00:01:08.410]We also have a risk of erosion,
[00:01:09.870]water erosion, soil erosion,
[00:01:12.840]and generally soil health issues such as aggregation,
[00:01:18.920]loss of organic matter,
[00:01:20.730]and other things which are a lot of times
[00:01:23.160]due to the fact that there is no crop growing,
[00:01:26.180]between the time of corn harvest and soybean planting.
[00:01:30.410]So we know that cover crops
[00:01:32.920]can help with some of these things.
[00:01:35.610]And today I'm talking mostly about cover crops influence
[00:01:38.170]on soil microbes.
[00:01:40.490]Cover crops are a food source for soil microbes.
[00:01:44.830]When they're growing during the winter
[00:01:46.530]or an early spring,
[00:01:48.530]or really any time of the year their root exudates,
[00:01:53.140]they're simple sugars amino acids
[00:01:54.750]and their preferred food for microbes.
[00:01:58.200]And of course the decomposing cover crop residue,
[00:02:02.090]also provides carbon and nitrogen to microbes.
[00:02:07.210]And that's both above ground and the below ground residue.
[00:02:12.360]Cover crops provide more than just a food source.
[00:02:15.090]They also provide habitat,
[00:02:17.360]roots are actually the preferred habitat for microbes.
[00:02:23.380]Most microbes live in the roots zone
[00:02:25.270]either near or on roots.
[00:02:29.010]And cover crops can also help mitigate
[00:02:32.660]soil surface micro-climates.
[00:02:34.420]For example by lowering the temperature
[00:02:38.070]preventing those temperature extremes
[00:02:40.350]and preventing wind or at slowing evaporation
[00:02:45.800]and things like that.
[00:02:47.720]So I wanna take a few minutes
[00:02:50.280]to just introduce some of those microbes
[00:02:52.240]that we have in the soil.
[00:02:54.390]Of course we all know
[00:02:55.820]that there's numerous little creatures that live there.
[00:02:58.960]So today, I'm mostly focusing on decomposers and predators.
[00:03:04.470]Our largest group of decomposers,
[00:03:07.540]in agricultural fields anyways are bacteria,
[00:03:10.120]they are the most numerous group of decomposers.
[00:03:13.800]And they preferentially decompose simple organic compounds.
[00:03:17.760]So that would be for example things like,
[00:03:21.000]freshly terminated cover crop.
[00:03:24.630]Anything that's easy to break down.
[00:03:27.903]And then we have fungi
[00:03:28.947]they are the other big group of decomposers.
[00:03:30.940]They keep decompose organic compounds
[00:03:34.250]that are harder, tougher.
[00:03:37.650]Things like cornstalks or roots
[00:03:41.470]and they play an important role for other things.
[00:03:44.630]And then we also have a lot of predators
[00:03:46.690]and I put up a picture of the soil food web.
[00:03:50.720]It all starts with plansts
[00:03:52.130]of course the source of organic matter.
[00:03:54.200]Then we have different decomposers
[00:03:56.030]that I just talked about.
[00:03:57.590]And the predators,
[00:04:00.900]some of them are protozoa which feed mostly on bacteria.
[00:04:04.050]We also have nematodes that are predatory.
[00:04:06.050]They feed on fungi and bacteria.
[00:04:08.550]So those predators really keep the populations of Bacteria
[00:04:15.426]and other soil microbes in check.
[00:04:19.780]A little bit more about the fungi.
[00:04:21.400]Why do we really like to see fungi?
[00:04:24.410]They're so important for soil aggregation.
[00:04:27.750]They have a thread like growth it's called hyphae,
[00:04:31.980]and they also release
[00:04:33.910]glue like substance called glomalin
[00:04:35.600]and those two together help bind little soil particles,
[00:04:41.170]and make those nice aggregates.
[00:04:42.500]So fungi improved aggregate size.
[00:04:45.620]They improve aggregate stability.
[00:04:48.430]And that makes soil much more resilient to erosion.
[00:04:54.320]Two large groups of fungi
[00:04:55.830]that we're interested in.
[00:04:56.790]One are the saprophytic fungi,
[00:04:58.520]they are the ones that decompose
[00:05:00.230]things such as cellulose and lignin.
[00:05:02.140]So that's the stuff that's found in corn stover.
[00:05:05.230]And then we have AMF or arbuscular mycorrhizal fungi,
[00:05:09.310]which colonize the roots.
[00:05:11.240]They can increase nutrient uptake
[00:05:13.010]because they can reach on nutrient sources
[00:05:16.020]that are otherwise not accessible to plant roots.
[00:05:21.470]When you have a cover crop growing over the winter,
[00:05:23.950]it can be a host to AMF,
[00:05:26.920]so it can live on the cover crop roots
[00:05:29.550]And then when the cover crop is terminated
[00:05:32.820]your sobering or con plant is planted,
[00:05:35.050]AMF can actually spread from the cover crop roots
[00:05:38.260]to the crop roots colonize the crop roots
[00:05:41.550]and have benefits for crops there as well.
[00:05:48.090]So this project we actually carried this project out
[00:05:51.380]at the soybean management field day sites.
[00:05:55.490]We worked together with Keith gluons
[00:05:57.900]and Justin McMakin steam.
[00:06:00.740]We had several research questions.
[00:06:02.010]Our first research question was can we use cover crops
[00:06:05.500]to reduce soil nitrate, before soybean?
[00:06:11.060]The second question was can rye cover crops,
[00:06:15.690]increase overall microbial abundance?
[00:06:18.540]And then we also wanted to know how different groups
[00:06:22.760]of soil microbes are influenced by a right cover crop.
[00:06:26.240]And in particular,
[00:06:27.550]we wanted to see whether we can increase
[00:06:30.060]the populations of soil fungi.
[00:06:33.610]So again these trials was set up
[00:06:37.260]at a soybean management field day sites.
[00:06:41.350]This year unfortunately due to COVID
[00:06:43.160]we were only able to do it at Arlington and Shelby.
[00:06:47.630]We had a right cover crop and we also had control crops.
[00:06:51.140]It was a replicated randomized design
[00:06:54.410]the rivals planted in mid November
[00:06:56.180]and then terminated at soybean planting in early to mid May.
[00:07:02.040]And then this was done by Keith Clunes
[00:07:05.460]and testing McMahon's teams.
[00:07:07.060]We came in just for the soil testing.
[00:07:10.170]So within a week of soybean planting we took soil tests.
[00:07:13.610]These tests are...
[00:07:16.710]They're only done to a sole depth of four inches.
[00:07:19.670]This is just because
[00:07:21.050]that's where most of the microbial activity is happening
[00:07:24.010]in the soil.
[00:07:25.430]We were testing the solve for NPK.
[00:07:27.570]So major nutrients,
[00:07:30.140]and the other tests we're doing is called PLFA
[00:07:33.120]or forceful lipid fatty acid analysis.
[00:07:38.940]This test to basically,
[00:07:41.640]to indicates what kind of microbial groups are in the soil
[00:07:48.360]by identifying the phospholipid fatty acids
[00:07:52.520]that are in the membranes.
[00:07:55.280]So it doesn't give me the type of species
[00:08:00.760]but certain functional groups for example AMF
[00:08:03.620]and separate phytic fungi and bacteria
[00:08:05.540]we can differentiate those.
[00:08:07.860]We carried out statistical analyzes with Brooklyn mix.
[00:08:11.697]And the differences that I'm talking about
[00:08:13.100]if there were significant differences
[00:08:14.710]they were different at alpha level of 0.05.
[00:08:21.600]So this is what we found.
[00:08:25.990]We had relatively low zero right biomass
[00:08:29.630]at our Arlington site about 1000 pounds
[00:08:31.760]and about 1,300 pallets at the Shelby site.
[00:08:38.480]We analyzed the biomass for carbon and nitrogen
[00:08:44.100]at the Shelby site
[00:08:44.960]it had pretty high amount of nitrogen,
[00:08:49.740]a little bit lower at the Arlington side.
[00:08:51.950]So these cover crops took up between 25 and 40 pounds
[00:08:56.180]of nitrogen per acre.
[00:08:58.260]And they had a carbon to nitrogen ratio of 19 and 14.
[00:09:02.270]So this carbon to nitrogen ratio is important
[00:09:05.547]because that kind of tells us a little bit
[00:09:08.140]about how fast the cover crop may decompose.
[00:09:13.360]Any time the ratio is below 25 to one,
[00:09:18.140]we expect it to decompose pretty quickly.
[00:09:21.050]And with those ratios said we have here
[00:09:23.420]we do think that that cover crop decomposes
[00:09:26.100]within the season for sure.
[00:09:30.180]Which also means that it releases its nitrogen
[00:09:32.450]that it took up back to the crop, okay.
[00:09:37.130]Moving into the soil nutrient concentrations
[00:09:39.540]following the cereal rhyme,
[00:09:41.950]we did see differences when it came to soil nitrate,
[00:09:45.930]again, this was a pretty shallow depth
[00:09:48.530]only zero to four inches.
[00:09:51.200]But at that depth we found
[00:09:53.260]that soil rye had significantly lower.
[00:09:56.720]So nitrate levels in May,
[00:09:59.750]at the time when we sampled.
[00:10:02.740]So the blue bars this is my control
[00:10:05.470]where we did not grow a cover crop.
[00:10:06.970]The red bars where we grow a CRO rye cover crop,
[00:10:12.350]As you can see significantly
[00:10:13.670]lower amounts of soil nitrate under the xx rye.
[00:10:16.960]So it takes up some of that nitrate
[00:10:18.530]possibly prevents it from leaching.
[00:10:22.200]In July when we came back in,
[00:10:24.940]there were still some smaller differences
[00:10:28.710]but overall probably some of that nitrogen
[00:10:32.870]from the rye residue had already decomposed
[00:10:35.870]and went back into the soil.
[00:10:39.200]We looked at the other soil nutrients,
[00:10:42.130]but I did not influence phosphorus potassium
[00:10:46.490]or organic carbon.
[00:10:48.360]So absolutely no differences there.
[00:10:51.370]We saw some side effects.
[00:10:53.270]The site at Shelby had more phosphorous
[00:10:55.090]than the site at Arlington,
[00:10:58.260]and decided Shelby also
[00:10:59.690]had less organic carbon than Arlington.
[00:11:02.800]With organic carbon
[00:11:03.720]we kind of expected that zero right cover crop
[00:11:06.300]would not influence that within the short amount of time
[00:11:08.710]that we've grown it.
[00:11:09.660]Does usually you need four or five years or more
[00:11:13.530]to really see differences in the organic carbon.
[00:11:16.270]It's much more determined by soil type really.
[00:11:22.910]So we tested microbial biomass in May as well.
[00:11:27.710]We also did not see any treatment differences
[00:11:30.410]that were due to the cover crop.
[00:11:31.960]And we actually did not see any site differences.
[00:11:33.900]So that was kind of interesting.
[00:11:36.430]So the two bars again, refer to the two sites.
[00:11:39.070]So we have our Arlington and our Shelby sites,
[00:11:42.400]And I just broke it down to give you kind of an overview.
[00:11:47.630]So the blue refers to bacteria.
[00:11:53.010]So they are out of all the groups the most numerous one
[00:11:56.250]in the soil.
[00:11:57.260]Then we have a very, narrow bar there of red
[00:12:03.100]which are the AMF fungi.
[00:12:04.340]So there are a lot less
[00:12:05.900]and to create a separate phytic fungi.XX
[00:12:07.610]So as you can tell fungi only make up
[00:12:10.570]about 10% or even less of the total of microbial biomass.
[00:12:15.170]And then we have a large amount of yellow which is others
[00:12:19.917]which are a lot of other,
[00:12:22.500]soil microbes such as actinomycetes,
[00:12:25.530]Brodo soul and some other nematodes
[00:12:28.230]and things like that are all looped in here.
[00:12:29.650]I did not actually separate them out
[00:12:33.700]because they're usually their numbers are very, very small.
[00:12:38.470]Cell but there's a lot of them, a lot of different groups.
[00:12:42.620]So no treatment differences, at least not in May,
[00:12:44.930]we have not gotten our results back from the summer.
[00:12:48.010]What we found last year, we did the same experiment
[00:12:51.720]we actually did see some increases
[00:12:54.390]in microbial communities following cereal rye.
[00:12:58.690]So I wanted to kind of figure out
[00:13:00.560]why did the rye not have an impact this year?
[00:13:04.840]I looked at my test results again and actually realized
[00:13:08.830]that the microbial biomass at our science
[00:13:14.710]even in the controls was already pretty high
[00:13:18.680]or at least it was average.
[00:13:21.240]So it's probably more difficult to increase it
[00:13:24.910]from populations that are already relatively high.
[00:13:33.050]Another thing that I looked
[00:13:34.060]at as the fungi to pictorial biomass, remember
[00:13:37.550]in agricultural fields
[00:13:38.570]we are really looking to increase the amount
[00:13:41.240]of fungi because they're so important
[00:13:43.120]for our soil aggregation,
[00:13:45.150]also structure and things like that.
[00:13:48.350]And here we actually saw a site difference.
[00:13:51.550]The Arlington side had a higher fungi to bacteria ratio
[00:13:55.400]but again it was not influenced by the rye treatment.
[00:14:01.780]So another thing I think
[00:14:03.760]if we wanted to really influence our
[00:14:07.860]microbial biomass a little bit more
[00:14:11.360]some of the things that we may want to look at...
[00:14:15.720]Oh, I forgot to talk about the organic carbon,
[00:14:17.920]organic carbon in these sites
[00:14:19.330]was also relatively high already.
[00:14:21.680]So again, these sites had relatively good soul health,
[00:14:26.840]probably a reason
[00:14:27.870]why we didn't see more treatment differences.
[00:14:31.410]How can we increase the benefits for soil microbes?
[00:14:34.540]How can we use a cover crop
[00:14:37.300]to really improve microbial abundance and diversity?
[00:14:43.300]We have only focused on Syria, right?
[00:14:45.090]There are plenty of other cover crop species out there.
[00:14:48.530]Mixing cover crops together probably could increase.
[00:14:54.780]Soil microbial diversity.
[00:14:57.150]It could also increase cover crop biomass
[00:14:59.070]at least during certain times of the year.
[00:15:02.520]And generally I think trying to increase cover crop biomass
[00:15:06.790]for example by allowing to grow with the cover crops
[00:15:09.870]for longer period of time would be beneficial
[00:15:12.570]for soil microbial communities as well.
[00:15:17.430]For my take home points,
[00:15:20.280]we do think we could use the right cover crop
[00:15:22.980]to really reduce Soil nitrate levels
[00:15:25.150]which could help reduce soil nitrate contamination
[00:15:30.725]and may reduce leaching.
[00:15:32.956]At least this year we did not see any improvements
[00:15:35.930]in soil microbial abundance.
[00:15:38.090]We have seen it in the past
[00:15:39.780]but this year we did not have very high cover crop biomass.
[00:15:45.540]Increasing cover crop biomass
[00:15:47.120]and probably increasing the amount of plant species,
[00:15:49.754]several growing mainly to create a benefits
[00:15:52.800]for soil microbes.
[00:15:54.840]And this is really the end of my presentation.
[00:15:56.670]I want to thank the participating farmers
[00:16:00.240]Keith and Justin, and their team
[00:16:02.379]George Biliarski who took all of the samples
[00:16:05.100]for this project.
[00:16:07.250]I also wanna thank our sponsors
[00:16:08.830]the Nebraska Soybean Board
[00:16:10.510]who partially funded this project
[00:16:14.221]along with the Nebraska Corn Board.
[00:16:16.010]And with that I take questions.
[00:16:18.210]So the question was
[00:16:19.840]if there is a greater amount of organic matter under soil
[00:16:23.550]with increasing organic matter in the soil.
[00:16:26.360]Are there greater amounts or greater diversity
[00:16:30.623]of bacteria and fungi.
[00:16:36.750]There's are definitely are greater amounts
[00:16:39.020]of them probably also greater diversity.
[00:16:47.460]With my tests I have not seen that
[00:16:49.380]because I generally do not look at different bacteria level.
[00:16:53.320]I look at just the total bacterial biomass.
[00:16:57.630]And as far as this test goes, I looked
[00:17:00.100]at just two groups of fungi, AMF, and separate phytic fungi.
[00:17:07.360]But I do think that from other papers that I read
[00:17:10.900]you can increase the diversity, especially
[00:17:14.540]in the amount for surely, especially that are fungi
[00:17:17.020]with increasing soil organic matter.
[00:17:20.080]So if they are interested in learning
[00:17:23.552]about specific functional groups
[00:17:26.670]of microbes, the PLFA test is a good test for that.
[00:17:34.130]It's a pretty expensive test
[00:17:36.330]and it's also a quite complex test.
[00:17:39.550]It's something they would have to
[00:17:40.840]but they would basically just take the soil sample
[00:17:43.560]and then send it to the lab.
[00:17:45.150]It takes several weeks to return it.
[00:17:49.490]There are some established parameters
[00:17:54.820]because the thing is
[00:17:57.070]this test gives you all these functional groups
[00:17:59.150]but what do the numbers really mean?
[00:18:01.780]So the nice thing about is there are some parameters
[00:18:05.450]some numbers that say
[00:18:07.060]okay, this is a good or desirable level
[00:18:09.760]and this not so much.
[00:18:13.563]So from that point of view you get some information back
[00:18:16.320]from the laboratory that you can actually use
[00:18:18.770]to interpret what your soils look like.
[00:18:21.410]So the question was how important is manure
[00:18:25.002]as a jumpstart to solve health?
[00:18:27.170]Thanks for bringing that question up
[00:18:28.710]because livestock is really or if you can graze then
[00:18:33.670]manure applications are really
[00:18:35.140]a very good way to increase microbial populations.
[00:18:41.870]First of all, there are microbes in the manure themselves
[00:18:45.120]and then just the amount of organic matter
[00:18:48.140]and other nutrients that are relatively easy to access
[00:18:52.600]for the microbes.
[00:18:53.610]That's really, really important.
[00:18:55.480]That's a very good thing to do for soil health.
[00:18:58.720]So the question was, is the optimum cell health
[00:19:03.420]the same for a corn field as for a range land
[00:19:06.746]or another type of cropping system?
[00:19:11.430]Yeah, that's a good question.
[00:19:12.810]I think like Keith said earlier
[00:19:17.580]maybe the standard really was, what was the soil
[00:19:20.890]like before it got turned into something else?
[00:19:25.040]So that's probably a good benchmark to try to maintain
[00:19:29.850]for a cropping system.
[00:19:30.960]Can you maintain that at a similar level?
[00:19:33.710]That may be very hard
[00:19:34.710]but maybe that native part
[00:19:37.450]that it replaced that was the benchmark.
[00:19:39.830]I do think there are exceptions though
[00:19:41.510]to that because some managed soils
[00:19:46.100]have really increased their fertility over what was before
[00:19:48.840]and that's due to probably irrigation, probably manuring
[00:19:52.970]we all can think of some very sandy lands
[00:19:55.620]that probably have been improved by people over time.
[00:20:01.098]So I think some things can be improved on,
[00:20:02.630]whereas others maybe not.
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