5 - 2020 South Central Ag Lab Field Day

Mike Kamm Author

12/04/2020 Added

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2020 South Central Ag Lab Field Day

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[00:00:03.480]Yep.
[00:00:04.310]Hi, my name is Sabrina Ruis
[00:00:05.900]I'm a research assistant professor at University of Nebraska Lincoln in the
[00:00:09.590]department of agronomy and horticulture.
[00:00:11.150]And I'm going to talk about a study that has been in place for six years,
[00:00:15.800]looking at cover crop termination date on soil properties and crop yields.
[00:00:21.620]So this topic is,
[00:00:23.660]an important topic because cover crops can have variable effects on soils and
[00:00:28.190]crops, depending on their management.
[00:00:31.790]So that cover crop management is going to drive
[00:00:36.770]the cover crop biomass production.
[00:00:38.480]So if you have a short window of growing those cover crops,
[00:00:42.020]they're not going to produce a lot of biomass,
[00:00:43.490]but if we can link them that window,
[00:00:45.860]then we're going to have theoretically more biomass.
[00:00:48.650]So that's part of what we're trying to do with this study by terminating cover
[00:00:51.740]crops early or late,
[00:00:55.580]is trying to get that more biomass and more impacts positive impacts to the
[00:01:00.080]soil.
[00:01:01.100]So we looked at the impacts of early and late terminated cover crops in a
[00:01:06.080]no-till continuous irrigated continuous corn system here out at South central ag
[00:01:10.880]lab.
[00:01:12.170]And it also has a sister study that is rain fed near I'm
[00:01:17.180]actually near Lincoln,
[00:01:18.590]but I'm going to focus on just the site here at clay center.
[00:01:23.180]And so we have a newcomer crop treatment and early terminate cover crop early
[00:01:28.010]termination means that we are terminating it anywhere from about
[00:01:32.600]two to four weeks before planting corn.
[00:01:36.770]And then we have a late terminated cover crop, which is terminated,
[00:01:40.460]roughly early to mid may kind of depending on the year.
[00:01:45.290]So we measured,
[00:01:48.590]each year we measure cover crop biomass in the spring at each termination date.
[00:01:53.030]And we also looked at, corn yield in the fall.
[00:01:57.140]And then in terms of soil properties,
[00:01:59.480]we looked at wet aggregate stability or water erosion,
[00:02:02.210]potential particulate organic matter or label organic matter,
[00:02:05.960]whichever you want to call it soil organic matter,
[00:02:10.160]initial water infiltration,
[00:02:12.980]compaction and thermal properties.
[00:02:17.030]So first we're going to talk about cover crop biomass production.
[00:02:21.110]And when we terminated the cover crops early, regardless of the year,
[00:02:24.950]we had less than one mega gram per Hector of biomass.
[00:02:27.890]But when we terminate late, we can get up to four and a half,
[00:02:31.880]4.75,
[00:02:34.520]mega grams per Hector of cover crop biomass production, which is really great.
[00:02:38.810]and I'll get to that, the impacts of that on yield,
[00:02:43.760]towards the end of this talk.
[00:02:46.550]So as far as the soils are concerned, first,
[00:02:49.850]I want to talk about what's called particular organic matter or label organic
[00:02:53.480]matter. Now, when we,
[00:02:57.200]when we looked at this in year three,
[00:02:59.530]we saw that the late terminated cover crop actually increased the particular
[00:03:03.460]organic matter, which is really good.
[00:03:06.460]and I'll get into the why and momentarily. And then again, in year six,
[00:03:11.470]we also saw that that, same,
[00:03:16.380]the impact of the late terminated cover crop,
[00:03:18.960]increasing particulate organic matter.
[00:03:21.240]Now particulate organic matter is really important. You it's,
[00:03:24.240]a microbial food source. So anything we can do to,
[00:03:29.070]boost that will improve our microbial activity,
[00:03:32.790]it'll improve the overall organic matter in the soil.
[00:03:37.410]And it'll also provide for better aggregation because as we
[00:03:42.330]may know, organic matter is,
[00:03:44.850]and the microbial action on that organic matter is what glues our soil particles
[00:03:49.380]and smaller aggregates together. Now,
[00:03:52.230]when we talk about organic matter on the next slide,
[00:03:55.350]and this is our total organic matter, in year three,
[00:03:59.010]we saw no effect of cover crop termination date, but in year six,
[00:04:04.260]we saw that the late terminated cover crops increased total organic matter,
[00:04:09.480]and they increased it by five, roughly five,
[00:04:14.220]grass per kilogram.
[00:04:18.570]Now we're going to talk a little bit about what aggregates stability and on this
[00:04:22.530]slide, you can see that I have both the rain fed and irrigated sites.
[00:04:25.620]We're going to focus on the irrigated site and in year three,
[00:04:30.840]the late terminated cover crop increased,
[00:04:33.780]what aggregates stability or aggregate size.
[00:04:36.510]And this means that those aggregates are going to be more stable in water.
[00:04:39.870]We can have big rain events.
[00:04:42.100]they're not going to be carried as easily because they're going to be larger in
[00:04:44.640]size. And the same story is true in year six,
[00:04:49.560]the late terminated cover crops increased our aggregate size.
[00:04:52.440]So we're seeing increased organic matter and increases in aggregate size.
[00:04:59.010]But what about compaction as our machinery sizes have increased?
[00:05:03.960]That is one thing that we are concerned about.
[00:05:07.110]but we saw no effect on compaction. We measured that in two different ways,
[00:05:11.430]bulk density,
[00:05:12.930]which is the massive stri soil over the volume of the soil.
[00:05:17.670]And then also penetration resistance,
[00:05:19.710]which is the resistance of the soil to a probing force that might be a root.
[00:05:23.760]It might be an earthworm and neither showed any effect of late
[00:05:28.470]terminate or cover crop termination date.
[00:05:32.010]now we're going to transition into soil, hydraulic properties just a little bit,
[00:05:35.910]and first we want to capture water.
[00:05:39.870]So we want the water to infiltrate into the soil and then we want to retain it.
[00:05:43.530]So we're going to talk about both pieces, water infiltration.
[00:05:47.250]We measured that in just the initial water infiltration.
[00:05:50.280]So we measured just a much smaller ring.
[00:05:53.430]If you've had any talks with Michael Cinderella,
[00:05:56.040]he might talk about a three test. we didn't do the three hour test.
[00:06:00.140]We just did the little short one that takes no more than 10 minutes. And,
[00:06:05.030]but we saw no effect of co cover crop termination date on water
[00:06:09.590]infiltration. as far as water retention,
[00:06:13.490]we have three different parameters that we look at for water retention.
[00:06:16.430]One is field capacity and that is the water content.
[00:06:20.630]After every, all the gravity drained water is gone,
[00:06:25.640]then we have the permanent wilting point, which is just,
[00:06:28.750]the water that's held so tightly to the soil that the plants can't get it.
[00:06:32.920]It's the point at which the plants will wilt and there's no rescuing them at
[00:06:37.090]that point.
[00:06:38.440]And now the difference between those two is what is called plant available
[00:06:41.770]water. And that's the one that we are generally most concerned about.
[00:06:47.230]And cause that's kind of our storage tank for,
[00:06:51.520]soil water and all three of those parameters,
[00:06:55.870]we saw no effective cover crop termination date,
[00:06:57.970]which is interesting because we saw increases in organic matter and
[00:07:02.560]increases in organic manner should be track with increases
[00:07:07.330]in, water content at field capacity or permit wilting point.
[00:07:13.810]another topic that is interesting to discuss with cover crops is the,
[00:07:19.390]thermal properties or the ability of the soil to conduct and transfer
[00:07:24.160]heat and increase in temperature. So we're going to talk about two,
[00:07:29.020]thermal properties. The first is thermal conductivity,
[00:07:32.740]which is the ability of the soil to conduct in transfer heat throughout the
[00:07:37.690]soil profile. The second is specific heat capacity,
[00:07:42.400]which is the,
[00:07:45.430]the amount of energy that it takes to raise the temperature of the soil.
[00:07:50.020]And when we look at the effect of cover crop termination date,
[00:07:54.670]late terminated cover crops,
[00:07:56.080]reduced thermal conductivity compared to no cover crop and early terminated
[00:07:59.830]cover crop. And that's probably because of the,
[00:08:04.150]increase in organic matter.
[00:08:07.360]soil minerals are going to transfer heat much more readily than organic matter.
[00:08:11.620]And that's part of what we're seeing there,
[00:08:13.480]but specific key capacity or the energy that we need to warm up that
[00:08:18.070]soil didn't change with cover crop termination date.
[00:08:23.920]So now I'm going to switch to the topic that you're probably all wondering
[00:08:27.820]about, crop yield.
[00:08:29.860]So I'm going to talk about this in two stages the first three years in the
[00:08:33.130]second three years. So in years, one, two through three,
[00:08:37.810]we saw that the late terminated cover crops reduced used
[00:08:43.030]crop yield in only one year.
[00:08:46.510]And then in the second set,
[00:08:48.970]we saw that the late terminated cover crops also reduced the crop yield
[00:08:53.740]in one year. So two out of six years, we saw reductions in crop yield.
[00:09:00.360]So in summary, after particular organic matter,
[00:09:05.010]after three and six years late terminated Kroeber crops increased organic
[00:09:09.900]matter was unaffected in year three,
[00:09:11.790]but late terminate cover crops increased compared to the early in the no cover
[00:09:16.050]crop.
[00:09:16.950]What I agree is stability or aggregate sized or water remotion potential late
[00:09:21.360]terminated cover crop increased after six years
[00:09:25.590]and after three years,
[00:09:27.720]water infiltration and compaction and plant available water and thermal
[00:09:31.830]properties were not measured in year three because they're a little bit slower
[00:09:34.170]to change with management. So after six years,
[00:09:37.950]water infiltration and compaction were not affected nor West plant available
[00:09:41.850]water, but late terminated cover crops, decreased thermal conductivity.
[00:09:46.440]And again, that goes back to the organic matter crop yields.
[00:09:51.390]Again, two out of six years,
[00:09:53.280]we saw reductions due to the late terminated cover crops. So
[00:09:59.610]what does that mean for you as a farmer? Well,
[00:10:03.090]if you are looking to see imp,
[00:10:06.510]improvements in your soil terminated at cover crops late is the way to go.
[00:10:11.340]But if you're concerned about yield,
[00:10:13.860]perhaps realizing that you might have some reductions and they weren't
[00:10:18.840]large reductions,
[00:10:20.940]in two out of six years or picking something in between,
[00:10:26.250]like between the early in the late,
[00:10:29.010]for your termination date might be the way to go to try and get some of those
[00:10:33.600]soil health benefits, but also preserve your crop yield.

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5 - 2020 South Central Ag Lab Field Day

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