Cover Crop Biomass Expectations

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05/02/2025 Added

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Seminar #4 of a four-part series on cover crop production by the University of Nebraska in collaboration with USDA NRCS.

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[00:00:00.000]I think with that, we should get started since it is at the hour, and I'm glad to see a number
[00:00:05.660]of people here with us this morning.
[00:00:07.120]My name's Andrea Baesha, I'm an associate faculty professor, research and teaching role
[00:00:13.100]at the University of Nebraska in the agronomy department, and I've been leading with a great
[00:00:18.320]team of folks, a collaborative agreement respective to looking at cover crops across Nebraska.
[00:00:24.140]And Vesh Thapa, who presented on our first webinar series, is going to share with you
[00:00:28.020]today some of the work we've been doing on this project and others specific to this question
[00:00:34.160]of how much cover crop biomass should we really expect in Nebraska.
[00:00:37.740]Again, building around our series on what are some of the common challenges, because
[00:00:42.180]a common issue is just, do I have enough time to plant and terminate this cover crop between
[00:00:50.200]my corn and soybean rotation really to get enough growth?
[00:00:53.840]So what's realistic to expect for Nebraska?
[00:00:56.080]That's going to be our topic today.
[00:00:57.260]So with that,
[00:00:58.020]I want to turn it over to Vesh and to Nathan for the formal presentation and discussion.
[00:01:04.900]Yeah, thanks, Andrea.
[00:01:07.460]Just a few logistics for the NRCS folks.
[00:01:10.860]Again, Nathan Mueller, the State Soil Health Specialist for NRCS.
[00:01:14.340]For those of you joining us from UNL as a part of this really good collaboration, thank you.
[00:01:19.900]For the NRCS folks, we will be putting together a feedback form through Microsoft Forms that
[00:01:26.460]we'll send out to gather.
[00:01:27.900]Your feedback on this webinar series, it's been fantastic, but we want to hear your thoughts
[00:01:32.740]and honest feedback and whether it's something that we should keep pursuing and maybe changes
[00:01:38.680]we might make in the future.
[00:01:39.880]So thanks in advance for your feedback and look for that probably coming out sometime
[00:01:45.440]in February.
[00:01:46.480]So thanks.
[00:01:47.380]I'll turn it over to Vesh.
[00:01:49.000]Yeah, thank you, Nathan.
[00:01:51.460]So good morning, everyone.
[00:01:54.380]I'm Vesh Thapa.
[00:01:55.700]I'm a postdoc at...
[00:01:57.820]Department of Agronomy and Horticulture.
[00:01:59.880]So today we are in our fourth session
[00:02:03.520]of this webinar series,
[00:02:05.020]and I would like to welcome you all.
[00:02:07.100]And we are excited about today's dialogue
[00:02:10.160]between NRCS and UNL Extension Educators.
[00:02:13.840]So to get started,
[00:02:15.840]we would like to launch a quick poll,
[00:02:18.380]just like in our previous session,
[00:02:20.400]to see where everyone is joining us from.
[00:02:23.260]So this poll helps us to group you by region
[00:02:27.740]for the breakout rooms,
[00:02:29.000]so that we can strengthen our connections
[00:02:32.540]between UNL Extension and NRCS.
[00:02:35.240]So Grace, please launch the poll now.
[00:02:38.260]So once we have enough responses,
[00:02:47.420]share the results and create the breakout rooms accordingly.
[00:02:57.660]Yeah, the plan for this morning is that
[00:03:01.780]I will present for about 40 to 45 minutes
[00:03:04.900]and then we will move into our breakout discussions.
[00:03:08.560]So we have facilitators assigned
[00:03:12.380]to keep the conversation moving and take notes.
[00:03:27.580]So yeah, thank you for your participation.
[00:03:32.720]I see 20 people responded to the poll
[00:03:57.500]I think you can end the poll now, Grace
[00:04:08.460]or just keep going, it's up to you.
[00:04:12.260]Okay, I think I'll begin my talk.
[00:04:27.420]Okay, so I think I'll go ahead.
[00:04:45.400]So we mentioned this during our previous calls too,
[00:04:49.840]but I would like to emphasize it again in today's session.
[00:04:53.520]So I really appreciate the number of extension items
[00:04:57.340]that Extension Educators have committed to join us.
[00:04:59.560]So if you are within our service area
[00:05:03.040]and looking to locate where Extension Educators
[00:05:06.300]in your region lies, this website,
[00:05:09.140]epd.unl.edu website is an excellent resource.
[00:05:15.000]So here we offer a wide range of extension programs
[00:05:27.260]on many topics, not just crops or water and livestock.
[00:05:31.920]There are also programs in areas such as rural development
[00:05:36.100]and youth programming.
[00:05:38.740]So you may already be aware of these options,
[00:05:41.960]but you can explore the full range of categories
[00:05:45.000]by using the Any Source feature.
[00:05:48.060]So I would like to remind that we build this webinar series
[00:05:55.200]around three key topics.
[00:05:57.180]How cover crops affect subsequent cash crop yield,
[00:06:01.580]their water use, and their return on investment.
[00:06:06.500]So I would like to offer a quick refresher
[00:06:08.920]from our past three webinars.
[00:06:11.340]In our first session on October 1,
[00:06:14.380]I presented some of the specific process
[00:06:17.360]through which cover crop influence cash crop yields.
[00:06:22.060]So I'm just giving a brief summary here too.
[00:06:26.140]So,
[00:06:27.100]research across farms, small plot experiments,
[00:06:30.480]and farmer surveys often shows that
[00:06:34.360]cover crops have a generally neutral effect on yields
[00:06:38.440]and legumes or mixed cover crops before corn
[00:06:42.880]can boost yield while late terminated grasses
[00:06:46.500]sometimes can reduce them in especially in dry years.
[00:06:50.560]Although studied less,
[00:06:53.540]wheat and soybean exhibit similar patterns,
[00:06:57.020]cereal rye before soybean tends to be less detrimental
[00:07:01.620]than it is before corn.
[00:07:03.380]And the last point I would like to emphasize is
[00:07:07.620]once the management learning curve is overcome,
[00:07:10.680]negative yield effects can be minimized
[00:07:13.300]and in many cases be avoided.
[00:07:15.900]I'm not going to go in detail on this slide.
[00:07:21.020]It is just a brief summary of some of the resources
[00:07:25.260]we discussed in our
[00:07:26.940]webinar sessions.
[00:07:28.180]I understand that in your portal,
[00:07:32.160]these papers we shared are organized,
[00:07:35.100]so you should have them as a resource.
[00:07:37.240]All these experiments took place in Nebraska,
[00:07:41.420]examining cover crops and their impact on yield.
[00:07:44.660]So that was the focus in our first webinar session
[00:07:48.600]in October.
[00:07:49.500]And in November, we focused on how cover crop
[00:07:54.520]affects water or how water
[00:07:56.860]is used by cover crops.
[00:07:58.340]And this concern commonly comes up because people worry
[00:08:02.260]that cover crops might use too much water
[00:08:05.000]before the gas crop season, right?
[00:08:06.620]So we hear this question a lot.
[00:08:08.460]But what I can tell you today as a quick summary
[00:08:14.180]is that cover crops do affect the entire water cycle
[00:08:17.960]from reducing evaporation and increasing infiltration
[00:08:22.440]to potentially impact soil water storage.
[00:08:25.820]And these,
[00:08:26.780]the effects can be positive.
[00:08:28.920]That research shows cover crops can reduce runoff
[00:08:32.480]and improve soil infiltration and soil storage capacity.
[00:08:36.800]However, in drier years,
[00:08:39.320]we sometimes can see cash crop yield reductions
[00:08:42.880]following a cover crop.
[00:08:44.300]While on the other hand,
[00:08:47.840]in wetter springs or seasons,
[00:08:50.020]cover crops can be beneficial by taking off excess moisture.
[00:08:54.320]So here, I would like to stress that
[00:08:56.700]effective management,
[00:08:58.600]especially in termination and planting timing,
[00:09:03.600]can help ensure that benefits
[00:09:06.980]outweigh any potential drawbacks.
[00:09:09.420]And again, here is a brief summary of the research
[00:09:15.000]we covered in November's webinar.
[00:09:17.820]So we have organized these resources for you,
[00:09:20.540]but I won't go through them in detail now.
[00:09:23.340]So this recap simply highlights the key points
[00:09:26.620]about the positive, sometimes it can be more complex,
[00:09:31.620]effects that cover can have on water use.
[00:09:35.180]So in December, we focused on cover crop return investment.
[00:09:41.620]So this recap simply highlights the key points
[00:09:45.300]about cover crop cost and return,
[00:09:48.580]saying that it can vary based on different assumptions
[00:09:51.840]and scenarios.
[00:09:53.340]A partial budget approach includes costs like
[00:09:56.540]seed labor equipment, along with possible revenues
[00:10:00.460]and like higher yields or grazing.
[00:10:03.600]And many farmers report positive returns after a few years
[00:10:07.960]and several tools like UNL Crop Budget Platform,
[00:10:12.120]the ABC Calculator, IOI State Net Returns Calculator,
[00:10:16.100]and reports from the Soil Health Institute,
[00:10:18.960]SARE program and American Farmland Trust provide,
[00:10:23.000]can provide some helpful guidance.
[00:10:25.500]So coming back to our today's session,
[00:10:30.140]so I'll be talking on how much cover crop biomass
[00:10:33.580]can we expect in Nebraska.
[00:10:36.200]So this is the outline of my presentation.
[00:10:40.500]So I'll be talking about introductions
[00:10:43.380]and why biomass really matters.
[00:10:45.980]And I will be talking on the factors
[00:10:48.540]influencing cover crop biomass productions
[00:10:51.500]and provide some of the research and evidence
[00:10:54.460]and
[00:10:55.300]give some of the take-home messages.
[00:10:57.740]And then we will move into the breakout room discussion.
[00:11:01.380]So I'll be talking about what is biomass
[00:11:05.700]and why that matters.
[00:11:07.340]So here, let me begin with the definition.
[00:11:12.540]So what is biomass, right?
[00:11:14.180]So biomass yield,
[00:11:16.020]it refers to the total amount of plant materials produced
[00:11:19.820]like leaves, stems, roots.
[00:11:23.220]So those,
[00:11:25.300]plant material produced per unit
[00:11:29.140]over a given period of time.
[00:11:30.900]So above ground, it means soot
[00:11:34.420]and below ground means roots.
[00:11:37.140]So I always emphasize and give equal importance
[00:11:40.540]to below ground productivity as above ground
[00:11:43.660]because it has been estimated that cover crops provide
[00:11:48.540]50 to 75% of their fixed carbon to soil through roots.
[00:11:54.060]And carbon derived from roots,
[00:11:57.220]it builds soil organic matter five to 30 times faster
[00:12:00.480]than above ground biomass.
[00:12:02.800]And as we all know,
[00:12:03.980]cover crops offer multiple ecosystem service benefits
[00:12:07.760]like they improve soil properties and processes,
[00:12:11.660]they helps to suppress weeds,
[00:12:13.840]they facilitate crop pollinators,
[00:12:16.420]they provide habitat for beneficial predatory insects,
[00:12:20.860]they can also serve as a forest source
[00:12:22.820]for livestock.
[00:12:25.060]However, the magnitude of these benefits
[00:12:29.160]provided by cover crops is always linked
[00:12:31.800]to their biomass production.
[00:12:33.760]So let me talk.
[00:12:37.540]So this is a meta-analysis in the US Midwest.
[00:12:41.240]So this meta-analysis has reported that a minimum biomass
[00:12:45.920]of five megagram per hectare is required
[00:12:48.840]to reduce weed biomass by up to 75%.
[00:12:52.740]So this is how we can see the importance
[00:12:55.360]of biomass production, right?
[00:12:57.740]And similarly, this study, so this is a laboratory study.
[00:13:02.120]So this study has indicated that at least five megagram
[00:13:06.520]per hectare of cover crop residue is necessary
[00:13:09.980]to maintain soil organic carbon in hot, dry agro-ecosystems.
[00:13:14.980]So this is another study from central grade plants
[00:13:20.540]that reported approximately
[00:13:22.660]six to 7.7 megagram of residue per hectare per year
[00:13:27.660]would be needed to maintain soil organic carbon stocks
[00:13:32.820]under limited irrigation.
[00:13:34.780]And this is another study that showed small grain cereals.
[00:13:41.720]They can yield about six megagram per hectare of biomass
[00:13:48.520]and can serve as a high quality forest source
[00:13:51.080]for livestock.
[00:13:52.580]And this is another study from Europe that suggested
[00:13:57.580]one megagram per hectare of biomass threshold
[00:14:00.360]is needed for soil nitrate reduction.
[00:14:03.560]So these are some of the few examples I want to show,
[00:14:06.740]like how the ecosystem service benefits we get
[00:14:11.740]from cover crop is linked to their biomass.
[00:14:14.660]So moving ahead, I'll be talking about some of the factors
[00:14:20.260]that influence biomass production.
[00:14:22.500]So biomass production, it depends on various factors, right?
[00:14:27.500]Like including species selection, climate,
[00:14:32.720]soil characteristics, and management practice.
[00:14:36.020]So in today's talk, I would just like to highlight
[00:14:39.020]the four major factors like species selection,
[00:14:42.940]climate, soil, and management practices.
[00:14:46.400]So let me begin with the species selection.
[00:14:49.160]So why is the species selection important?
[00:14:51.580]It is because
[00:14:52.420]adaptation of cover crop species
[00:14:55.280]determines their productivity, right?
[00:14:57.380]And productivity can vary within the same spaces
[00:15:01.420]due to differences in plant hardiness
[00:15:04.080]or local landscape features.
[00:15:06.160]And moving ahead to climate,
[00:15:09.440]as we all know,
[00:15:11.040]biomass accumulation is highly dependent on weather, right?
[00:15:14.660]Especially precipitation and temperature
[00:15:17.460]where like warm, wet growing season typically produce
[00:15:22.340]more biomass than a cool, dry season.
[00:15:24.900]And moving ahead to soil properties,
[00:15:28.040]particularly organic matter content,
[00:15:30.720]nutrient availability and water retention capacity,
[00:15:34.580]they significantly affect biomass production.
[00:15:37.320]For example, soils which are rich in organic matter,
[00:15:41.580]they enhance nutrient cycling and storage.
[00:15:44.400]They improve soil structure, increase water retention,
[00:15:49.120]and these all promote higher biomass yield, right?
[00:15:52.260]So with regards to management factors,
[00:15:55.000]planting and termination dates,
[00:15:57.460]they play a vital role in biomass production
[00:16:00.440]because these dates determine the length of the growing period
[00:16:05.600]and environmental conditions to which cover crops are exposed.
[00:16:09.780]For example, early planting and late termination,
[00:16:14.620]they typically allow for higher growing degree days accumulation.
[00:16:18.860]And also, if we have
[00:16:22.180]early fall planting, they improve the survival chances during winter.
[00:16:27.480]So that's leading to greater biomass yield.
[00:16:31.160]In contrast, if there is late planting and early termination
[00:16:35.860]that result in reduced yield because of shorter growing periods
[00:16:40.000]and suboptimal growing conditions.
[00:16:43.500]And some literature has reported that
[00:16:47.000]planting beyond October 5, it leaves insufficient heat units
[00:16:52.100]for extensive cover crop growth and development.
[00:16:55.140]So that can result in reduced biomass yield.
[00:16:59.140]So here in this slide, I would like
[00:17:07.980]to highlight again why cover crop species selection
[00:17:11.860]is important.
[00:17:12.920]So species selection is a critical factor
[00:17:16.540]because, as I already mentioned, it
[00:17:19.240]influences the adaptability and productivity
[00:17:22.020]of cover crops.
[00:17:23.260]But how, right?
[00:17:24.180]So it is because different species
[00:17:28.340]will have different inherent traits that
[00:17:31.500]determine their competitive ability and complementarity
[00:17:35.620]under specific environmental conditions.
[00:17:38.920]So I would like to explain this with an example.
[00:17:41.540]For example, grasses are more adaptive
[00:17:44.280]to adverse environments.
[00:17:46.340]So they have a dense fibrous root system,
[00:17:49.300]and they can excel water.
[00:17:51.940]They have more nutrient and sunlight acquisition,
[00:17:54.560]so which supports robust growth and production.
[00:17:59.020]And grass species, they only not produce high biomass,
[00:18:03.160]but they also have higher Sheehan ratio, which is
[00:18:06.340]typically greater than 25:1.
[00:18:09.940]So this means this highlights the utility of grass cover
[00:18:14.800]crops for increasing soil carbon inputs,
[00:18:17.520]because if there is higher Sheehan ratio, their residue
[00:18:21.860]composition is more slow.
[00:18:24.540]That contributes to soil organic matter buildup.
[00:18:27.740]However, with legumes, because of their nitrogen fixing
[00:18:32.220]ability, they can perform well in nitrogen-deficient soils.
[00:18:37.280]Similarly, brassica offer benefits such as soil aeration
[00:18:42.360]because of their deep rooting system.
[00:18:45.100]But compared to grasses, both legumes and brassicas are more
[00:18:51.780]sensitive to climatic structures.
[00:18:54.600]So they are more sensitive to climatic extremes.
[00:18:59.880]But when they are included in the mixture, what happens?
[00:19:03.360]When all these grasses, legumes, or brassicas
[00:19:06.240]are included in the mixture, that functional differences
[00:19:09.840]among the species, they enhance the resource use efficiency
[00:19:13.540]as they fill distinct ecological niches,
[00:19:16.780]and they collectively boost overall productivity.
[00:19:20.140]So this is how--
[00:19:21.700]selection of cover crop species is important,
[00:19:27.280]as it influences the adaptability and productivity
[00:19:29.920]of cover crops.
[00:19:30.860]So in this slide, I would like to focus
[00:19:39.380]on why we should consider the range over mean wine
[00:19:44.440]estimating biomass.
[00:19:46.360]So mean-- so we all know it is the average biomass
[00:19:51.620]yield, right?
[00:19:52.460]While mean is useful, it does not
[00:19:54.920]capture the full story of how cover crops are performing.
[00:20:00.140]But when it comes to range--
[00:20:02.760]so range, it refers to the variability in biomass yield.
[00:20:06.920]It includes both the minimum and maximum yields observed.
[00:20:12.220]So then why is range important over mean?
[00:20:15.120]So it's because, as we all know, different regions
[00:20:19.760]will vary in their soil type.
[00:20:21.540]So water availability or sunlight exposure.
[00:20:24.300]And they all can lead to different kinds of yield.
[00:20:28.140]So focusing only on mean might overlook those variability
[00:20:33.060]in biomass yield.
[00:20:34.500]So understanding the range helps us
[00:20:37.900]to know the potential low yield areas
[00:20:41.540]and make informed decisions to improve consistency.
[00:20:45.340]For example, a wider range, it means
[00:20:48.780]there is more variability, and which could
[00:20:51.460]indicate a need for better management practices
[00:20:54.540]or adjustment in inputs.
[00:20:56.900]So in the slide--
[00:20:58.460]so this study, I'm giving you as an example.
[00:21:02.120]So this study includes about 6,000 observations
[00:21:06.540]across 208 site years in the eastern half of the US.
[00:21:11.460]And this study found that cereal rye biomass,
[00:21:15.460]it ranges from 265 to more than 6,000 kg per hectare.
[00:21:21.380]So you can see the range of biomass produced, right?
[00:21:26.000]So similarly, this is another study.
[00:21:30.180]So this is a review of about 400 papers.
[00:21:34.220]And it also indicated the range of biomass production.
[00:21:37.760]You can see from 410 to even more than 6,000 kg per hectare.
[00:21:43.380]So if we would have only focused on mean,
[00:21:46.420]so you can see like mean is about 3,000 kg
[00:21:51.300]per hectare, but if you see the range,
[00:21:53.840]you can see the lowest potential areas with even 410.
[00:21:58.140]So that is how I would like to focus,
[00:22:01.020]like instead of considering mean,
[00:22:04.660]we always need to consider range when it comes
[00:22:07.540]to explaining biomass estimates.
[00:22:09.920]So now I would like to move ahead
[00:22:14.260]in the context of Nebraska.
[00:22:16.640]So Nebraska, so you can see Nebraska's annual precipitation,
[00:22:21.220]is widely from west to east,
[00:22:23.680]ranging from 13 to 35 inches.
[00:22:27.380]So this east-west precipitation gradient,
[00:22:30.640]it has created distinct climatic conditions
[00:22:34.360]and soil types across Nebraska.
[00:22:37.300]For example, eastern region,
[00:22:39.860]it receives higher amount of precipitation
[00:22:42.600]and they have low evaporative potential.
[00:22:45.440]So this means that tends to have,
[00:22:48.400]the soils in the eastern part of Nebraska tends to have
[00:22:51.140]higher organic matter content and better water availability.
[00:22:55.020]They all support greater biomass production.
[00:22:59.220]However, in western regions it receives lower precipitation
[00:23:03.760]and have higher evaporative potential.
[00:23:06.760]So soils in this region are low in organic matter content
[00:23:11.120]and have reduced water availability.
[00:23:14.060]So they limit biomass yield.
[00:23:16.500]So these differences in regional climatic conditions and soils
[00:23:21.060]are of all type that emphasize the necessity of region-specific management strategies
[00:23:27.060]to optimize biomass production.
[00:23:29.060]And when it comes to variability in biomass production,
[00:23:33.060]it is often related to year-to-year differences in temperature and precipitation.
[00:23:39.060]For example, if there is above average temperature and precipitation,
[00:23:45.060]which is about during the cover crop growing period,
[00:23:48.060]like let's say it could be 15 degrees centigrade,
[00:23:50.980]and more than 300 millimeter of rainfall,
[00:23:53.980]they are generally associated with higher yields.
[00:23:56.980]Whereas if there is below average condition, they tend to reduce yield.
[00:24:01.980]And since this year-to-year variation in weather factors are very common,
[00:24:08.980]we cannot expect a substantial amount of biomass in every year.
[00:24:13.980]And specifically in Nebraska,
[00:24:15.980]there is a high level of inter-annual and inter-seasonal variability
[00:24:20.900]in climate, and we also get recurring periods of intense drought.
[00:24:25.820]And of course, the western part of Nebraska receives strong winds too.
[00:24:33.820]So therefore, understanding this variability in biomass production
[00:24:37.820]during the winter growing period is crucial for setting realistic expectations,
[00:24:43.820]because diverse conditions can occur during winter.
[00:24:50.820]We're going to talk about some of the research evidence from Nebraska
[00:24:54.740]that shows the variability in biomass production.
[00:24:57.740]So we reviewed the biomass yield of four cover crop species,
[00:25:04.740]like rye, tritical, wheat, and canola,
[00:25:07.740]across diverse locations and planting regimes in Nebraska.
[00:25:12.740]So what we wanted to see was we want to generate a spectrum of biomass estimates
[00:25:18.740]for these species of interest.
[00:25:20.740]So in this study, our goal was to see how seasonal variation in biomass production
[00:25:29.160]production across Nebraska, particularly in response to harsh winter conditions and we
[00:25:35.360]wanted to assess whether that seasonal differences result in variable outcomes without any season
[00:25:41.700]being consistently exceptional or unfavorable.
[00:25:46.820]And then for this review, biomass measurements for this species were taken from various sampling
[00:25:53.640]times ranging from early fall to late spring of the following year.
[00:25:59.240]And that accounted for different precipitation gradients and soil types.
[00:26:04.540]And the majority of the studies for this review were from eastern Nebraska, while there were
[00:26:10.580]fewer studies from central and western part of the states.
[00:26:15.260]So what we observed from this review of 18 studies, that it revealed that among the studies
[00:26:23.420]that we had taken, there was about 1.5 million species of biomass in the western part of the state.
[00:26:23.420]So what we observed from this review of 18 studies, that it revealed that among the studies that we had taken, there was about 1.5 million species of biomass in the eastern part of the state.
[00:26:23.520]So what we observed from this review of 18 studies, that it revealed that among the studies that we had taken, there was about 1.5 million species of biomass in the eastern part of the state.
[00:26:23.620]So what we observed from this review of 18 studies, that it revealed that among the studies that we had taken, there was about 1.5 million species of biomass in the eastern part of the state.
[00:26:53.600]So you can see, if we would have focused only in the mean, so we would just report about 2,000 kg per hectare.
[00:27:01.220]But when we are considering the range, so we found the range was from 100 to more than 7,000 kg per hectare in this review.
[00:27:09.460]And in the same review, we further classified those studies based on the precipitation zones.
[00:27:19.700]So we classified it into three precipitation zones.
[00:27:23.580]One as a humid, transition, and semi-arid region.
[00:27:28.420]So semi-humid means precipitation within the range of 700 to 850 millimeter.
[00:27:39.680]And transition means within the range of 550 to 700.
[00:27:43.740]And semi-arid means less than 550.
[00:27:46.160]So what we found when we categorized by precipitation zone, majority of the studies were conducted in
[00:27:53.560]semi-humid region and followed by transition zones and semi-arid regions.
[00:27:59.140]So depending on the species, in semi-humid regions, biomass production
[00:28:06.420]ranges from 100 to more than 7,000 kg per hectare.
[00:28:10.900]And in transition zones, from 270 to about 4,000 kg per hectare.
[00:28:17.380]And in semi-arid regions, from 110 to over 4,000 kg per hectare.
[00:28:23.540]And across these, in semi-humid region,
[00:28:28.720]so across all three grass species, like rye, tritical, and wheat,
[00:28:33.460]they showed an average biomass production of about 2,000 kg per hectare.
[00:28:38.740]So you can see the range of biomass production
[00:28:43.640]for each species in different precipitation zones.
[00:28:47.780]So this is another field study
[00:28:53.520]where four cover crop species, the same winter wheat, rye, tritical, and canola
[00:28:59.900]were grown and monitored in a spider camp experiment
[00:29:03.840]at NREC near Mead in eastern Nebraska.
[00:29:06.620]So this unique phenotyping site,
[00:29:10.200]so you can see in the picture on the left too,
[00:29:13.140]so this site is equipped with an automated cable suspended carrier system
[00:29:18.500]that accommodates multiple cameras and various types of sensors
[00:29:23.500]and those on-site sensors and the camera,
[00:29:27.760]it can capture the data on a plot scale
[00:29:32.820]at a sub-weekly time interval.
[00:29:36.780]And for this experiment,
[00:29:39.820]cover crops were drilled in September of both 2021 and 2022
[00:29:44.780]and terminated in May of the following year.
[00:29:48.500]So in this study, we were also interested to test the
[00:29:53.480]ability of APSIM model to predict biomass production
[00:29:57.460]using data from this unique phenotyping experiment.
[00:30:00.940]So our goal was also to compare how
[00:30:05.560]well the model predicted results align with the previously
[00:30:09.700]published data from the state, which is the review I talked in the previous
[00:30:13.480]slide. So you can see figures on the right.
[00:30:17.600]It shows that seasonal weather conditions
[00:30:21.700]made each
[00:30:23.460]year cover crop growth uncertain. So you can
[00:30:27.460]see wheat and rice survived in both winters, well as
[00:30:31.560]tritical and canola did survive in only one of the winters.
[00:30:35.620]So over the two years,
[00:30:38.760]there was significant differences in biomass yield.
[00:30:42.960]So in the first two figures on the top,
[00:30:47.400]you can see wheat and rye in the first growing season
[00:30:51.040]soared significantly higher.
[00:30:53.440]than the second year.
[00:30:55.080]Whereas tritical and canola were winter-killed in the second year
[00:31:00.340]due to unusually dry and cold winter.
[00:31:04.420]And since our goal was to test the ability of FC model,
[00:31:08.720]so we found that the model demonstrated
[00:31:11.660]moderate to high accuracy across species and years.
[00:31:16.820]And whatever the predictions,
[00:31:19.200]those were all aligned within the range found
[00:31:23.420]in the literature review.
[00:31:25.120]But I had to acknowledge that the model showed less efficacy
[00:31:30.020]under extreme conditions like winter kill.
[00:31:32.780]And in this slide, I'm going to talk about
[00:31:38.780]the importance of planting and termination timing.
[00:31:41.820]So as we all know, weather parameters like precipitation
[00:31:46.460]and solar radiation largely dictate cover crop growth,
[00:31:49.880]but management practices such as
[00:31:53.400]planting and termination timing, as well as species selection,
[00:31:57.180]they also significantly influence biomass production.
[00:32:00.660]So in this study, we were also interested to understand
[00:32:06.360]how growing interval impact the potential biomass production
[00:32:11.660]of a given species at a given location.
[00:32:14.680]So therefore, what we did is we coined the term
[00:32:19.520]called cover crop growth gap, and we calculated
[00:32:23.380]that cover crop growth gap as the difference between
[00:32:27.620]maximum biomass yield under extended growing intervals
[00:32:33.200]and the minimum biomass yield under shorter growing intervals.
[00:32:36.920]So basically, this gap, it represents the difference
[00:32:41.860]between the actual biomass yield achieved under
[00:32:45.520]shorter growing intervals and the potential biomass yield
[00:32:49.160]under extended growing intervals.
[00:32:53.360]This cover crop growth gap is pretty much analogous
[00:32:57.860]to commonly used methods in the literature
[00:33:00.480]for estimating yield gap,
[00:33:02.300]like comparing potential yield versus actual yield.
[00:33:05.780]So it is pretty much similar.
[00:33:07.640]So in this analysis, we utilized a historical weather dataset
[00:33:12.640]that range for about 37 years.
[00:33:16.540]So I'm going to talk about these figures.
[00:33:19.720]So in the figures on the left, so you can see
[00:33:23.340]the extended interval is indicated with blue color
[00:33:27.780]and the shorter interval with green color.
[00:33:31.020]So this growth gap was calculated
[00:33:34.820]for eight climatic divisions of Nebraska.
[00:33:38.640]And what we found from this calculation was on average,
[00:33:43.640]when planting in the shorter growing interval,
[00:33:47.680]the magnitude of gap range from a loss of 21% in the north
[00:33:53.320]central to 53% in the southwest for wheat.
[00:33:57.480]Similarly, 27% in the north central to 67% in the southwest
[00:34:02.480]for rye and 23% in the north central to 58% in the southwest
[00:34:07.900]for tritical and 20% in the northeast to 43% in the
[00:34:13.480]southwest for canola compared to an extended interval.
[00:34:18.020]So we were also interested to
[00:34:23.300]explore the impact of various planting and termination timing
[00:34:26.920]on biomass production within each county level.
[00:34:30.560]So in this analysis, we considered three planting dates
[00:34:35.100]like mid-September as a September 14, late September
[00:34:39.960]as September 27 and early October as October 10.
[00:34:44.640]And we had three termination dates, too, which is mid-April,
[00:34:49.180]which is April 13, late April is April 26.
[00:34:53.280]And early May as May 9.
[00:34:55.060]So what we found from this cover crop growth gap at county level.
[00:35:00.840]So results showed increased biomass production
[00:35:04.640]with extended growing in periods across all species.
[00:35:08.060]But here I'm going I'm showing the figure only for rye.
[00:35:12.300]So you can see in the figure, like specifically planting
[00:35:18.060]from mid to late September and termination in early May of the fall.
[00:35:23.260]Following year, particularly in the southeast, northeast and east central
[00:35:29.120]and south central too, it displayed the potential for higher biomass production.
[00:35:34.920]However, planting in late September to early October
[00:35:39.060]and termination in mid to late April of the subsequent year,
[00:35:42.860]especially in the panhandle, north central and southwest region,
[00:35:47.620]it showed lower biomass yield across all species.
[00:35:50.960]So in this region, maybe,
[00:35:53.240]extreme cold temperature, limited sunlight,
[00:35:55.940]and scarce water availability might have led to lower biomass yield.
[00:36:01.680]So if planting is delayed and termination is early,
[00:36:06.540]there is a gap, there is the potential to have a gap
[00:36:09.980]or loss of approximately 924 to more than 3,000 kg per hectare for wheat
[00:36:17.820]and about 2,000 to about 5,000 kg per hectare
[00:36:23.220]for rye and from so forth for tritical and canola.
[00:36:28.240]So in this slide, what I would like to highlight,
[00:36:31.600]so these gaps you can see on the table on the bottom right,
[00:36:36.860]so these gaps underscore the critical impact
[00:36:40.320]of growing intervals on biomass production.
[00:36:42.760]So this cover crop growth gap,
[00:36:46.300]so I would like to highlight here that
[00:36:48.180]so this cover crop growth gap gives an idea of the potential
[00:36:53.200]biomass loss due to delayed planting and early termination
[00:36:56.860]or the potential increase with early planting
[00:37:00.260]and delayed termination.
[00:37:01.960]So this is another simulation study from Stern, Nebraska
[00:37:07.920]that tested various rye planting dates in the fall
[00:37:12.560]versus one termination date in the spring,
[00:37:15.320]which was April 14 over two years in 2015 and 2016.
[00:37:20.380]You can see on the x-axis
[00:37:23.180]there are different planting dates for the fall.
[00:37:27.680]And so these results from this study
[00:37:31.520]showed that biomass production varied by planting dates.
[00:37:35.560]So you can see here the green color
[00:37:38.540]is the actual biomass harvested in the field.
[00:37:41.700]So biomass production varied by year,
[00:37:46.220]sorry, varied by planting dates in both years
[00:37:48.900]with the highest production for earliest planting dates
[00:37:53.160]in both years.
[00:37:54.080]You can see the cover crops when planted in 2015
[00:38:01.500]and terminated in 2016,
[00:38:03.200]it showed exceptionally high biomass.
[00:38:05.500]So earlier planting dates between mid-September
[00:38:10.220]and early October,
[00:38:11.220]it pretty much doubled the amount of biomass
[00:38:14.040]compared to late October planting dates for both the years.
[00:38:18.060]So this highlights that seasonal weather conditions
[00:38:23.140]can make each year cover crop growth uncertain.
[00:38:26.400]In the same study,
[00:38:30.960]so cover crop growing season,
[00:38:32.980]which was from September to April,
[00:38:35.020]were classified based on above or below average moisture and temperature.
[00:38:40.380]So here in the figure,
[00:38:42.160]you can see cool and dry means
[00:38:44.960]it is temperature below 15 degrees centigrade
[00:38:48.380]and precipitation below 225 mm,
[00:38:51.580]indicated by the temperature
[00:38:53.120]and warm and dry means greater than 15 degrees centigrade
[00:38:57.440]and less than 225 mm
[00:38:59.340]and cool and wet indicated by green color means
[00:39:03.320]less than 15 degrees centigrade
[00:39:05.800]and greater than 225 mm
[00:39:08.580]and warm and wet was classified as
[00:39:11.580]with temperature greater than 15 degrees centigrade
[00:39:15.140]and precipitation more than 225 mm.
[00:39:18.800]So in this figure,
[00:39:21.560]so,
[00:39:23.100]rye spring biomass was generated for planting dates
[00:39:26.820]starting from September 15 to October 31
[00:39:31.040]using a historical weather data set
[00:39:34.480]that were factored in the weather variabilities.
[00:39:37.200]So rye was terminated on April 15,
[00:39:41.400]irrespective of planting dates.
[00:39:43.760]So the results obtained from this study was
[00:39:48.500]earlier planting that occurred
[00:39:51.700]exceptionally high biomass
[00:39:53.080]in warm wet season
[00:39:55.020]and moderate in cool wet and warm dry seasons
[00:39:59.480]and low biomass in cool dry seasons.
[00:40:02.020]And you can see in the figure too,
[00:40:05.680]so there was 10 times more biomass was observed
[00:40:09.540]when planted in mid-September
[00:40:11.820]compared to late October.
[00:40:13.780]So in each identical planting dates,
[00:40:18.840]so the warm wet season,
[00:40:20.920]which is indicated by the purple,
[00:40:23.060]color,
[00:40:23.320]produced approximately four times more biomass
[00:40:27.180]than a cool dry season.
[00:40:29.060]So on average,
[00:40:31.820]during a six weeks fall planting window
[00:40:34.820]from September 15 to October 31,
[00:40:37.800]every day before October 31
[00:40:40.740]that the rye was planted
[00:40:42.720]resulted in additional biomass
[00:40:45.960]of 55 pounds per acre.
[00:40:47.980]So when averaged across all seasons,
[00:40:53.140]so if we delay rye planting
[00:40:55.580]from mid-September to October end,
[00:40:57.680]it can result in a loss of biomass
[00:41:00.140]by about 89%.
[00:41:03.120]Again, that study also tested
[00:41:07.380]a range of termination dates
[00:41:08.960]to determine how delaying termination
[00:41:11.420]in spring might affect rye biomass
[00:41:14.120]with the consideration
[00:41:15.700]of seasonal weather variability.
[00:41:17.420]So you can see on the x-axis,
[00:41:19.980]so rye spring biomass was generated
[00:41:23.020]for termination dates
[00:41:24.800]starting from April 1 to April 30.
[00:41:28.120]And for this, rye was planted
[00:41:30.820]on October 10,
[00:41:31.860]irrespective of termination dates.
[00:41:33.800]So here you see,
[00:41:36.220]there was no differences
[00:41:38.920]in biomass yield between warm, dry,
[00:41:41.680]and cool, wet season
[00:41:43.140]for any of the termination date.
[00:41:44.880]However, there was four times
[00:41:49.100]more biomass was observed
[00:41:51.120]when terminated in April
[00:41:53.000]and versus April 1st.
[00:41:55.260]So the key thing
[00:41:57.060]I would like to highlight here is
[00:41:58.580]everyday delay in rye termination
[00:42:01.500]resulted in an additional biomass
[00:42:03.780]of 31 pounds per acre per day.
[00:42:06.780]So when averaged across all seasons,
[00:42:10.880]so delaying rye termination
[00:42:13.140]from April 1st to April 30,
[00:42:15.660]it can result in an increase
[00:42:17.900]of biomass by about 284%.
[00:42:22.980]So in this slide,
[00:42:26.040]I would like to talk about
[00:42:28.140]how planting practice
[00:42:29.840]influenced cover crop biomass yield.
[00:42:31.720]So this study was conducted
[00:42:34.880]in 2014 through 2018
[00:42:37.060]in Stern, Nebraska at three sites.
[00:42:39.820]They were Clay Center, Concord, and Mead.
[00:42:42.440]So planting practices
[00:42:46.180]were pre-harvest broadcast
[00:42:48.480]interseeding in corn and soybean stands
[00:42:50.760]and post-harvest drills
[00:42:52.960]seeding after corn and soybean harvest.
[00:42:55.120]And all the experimental plots
[00:42:57.740]were under no-till management
[00:42:59.800]and cover crops were broadcasted
[00:43:02.840]when corn reached R5 growth stage
[00:43:07.740]and soybean was at R6 growth stage.
[00:43:10.180]And in all of the sites,
[00:43:12.980]cover crops were terminated
[00:43:14.740]at following spring,
[00:43:15.940]which was about two weeks
[00:43:17.860]before corn planting or soybean.
[00:43:20.660]So what I would like
[00:43:22.940]to highlight here
[00:43:23.820]was the cover crop treatments
[00:43:25.240]were rye, the mixture one,
[00:43:28.020]and mix two, and the legumes.
[00:43:29.940]And the results showed
[00:43:32.800]that at the sites
[00:43:34.220]with wet fall weather,
[00:43:36.140]pre-harvest broadcasting
[00:43:37.780]increased biomass by 90%
[00:43:39.840]for rye and 0.87 megagram
[00:43:43.560]per hectare for mixture one
[00:43:45.280]and in soybean corn
[00:43:46.820]and to 0.56 megagram
[00:43:49.140]per hectare to 0.39 mega,
[00:43:52.920]gram per hectare in corn,
[00:43:54.340]continuous corn respectively.
[00:43:56.780]Whereas at the drier side,
[00:43:59.340]post-harvest drilling
[00:44:00.780]increased biomass of rye
[00:44:02.480]and mix one by 95%
[00:44:05.300]to 0.8 megagram per hectare
[00:44:07.540]in soybean corn.
[00:44:08.760]So what I would like to highlight
[00:44:11.360]from this slide is that
[00:44:12.940]early planting of cover crops,
[00:44:15.420]if combined with warm temperature
[00:44:17.720]and relatively high precipitation
[00:44:19.320]in fall through spring,
[00:44:20.820]it can improve biomass,
[00:44:22.900]production compared to cold
[00:44:25.520]or dry fall or in spring
[00:44:28.180]and with minimum snowfall.
[00:44:30.040]So in this slide,
[00:44:34.520]I wanted to talk about
[00:44:36.820]how biomass production
[00:44:38.740]can differ between years
[00:44:40.360]within the same site
[00:44:41.960]and growing conditions.
[00:44:43.260]So this study was conducted
[00:44:46.740]at Sydney, Nebraska
[00:44:47.920]during 2012 and 2013
[00:44:50.800]growing seasons under both
[00:44:52.880]rain-fed and irrigated conditions.
[00:44:54.480]And the study location
[00:44:56.480]had a silt loam soil.
[00:44:58.320]And the cropping system
[00:45:00.920]investigated had,
[00:45:02.440]was a no-till prosomillate
[00:45:05.120]spring cover crop
[00:45:06.460]winter wheat rotation.
[00:45:07.680]And all cover crop treatments
[00:45:10.680]were no-till seeded
[00:45:12.840]into prosomillate residue
[00:45:14.780]left following prosomillate
[00:45:18.040]harvest the previous September.
[00:45:20.160]So here I would like to
[00:45:22.860]highlight the percentage change
[00:45:25.020]brought by irrigation
[00:45:26.580]over dry land.
[00:45:27.540]So you can see in 2012,
[00:45:29.760]for example,
[00:45:32.300]irrigation brought
[00:45:35.600]like 47% more biomass
[00:45:38.220]compared to dry land
[00:45:39.680]for the flax.
[00:45:40.520]But you can see
[00:45:41.720]the average biomass production
[00:45:44.140]indicated in a green color,
[00:45:45.760]like in 2012,
[00:45:46.980]dry land has
[00:45:48.660]average production of 2,184.
[00:45:52.840]Whereas in the same study site
[00:45:54.980]in 2013,
[00:45:56.260]there was an average production
[00:45:58.220]of 4,224.
[00:45:59.960]And similarly for irrigated sites
[00:46:02.160]as well,
[00:46:02.640]there was differences
[00:46:03.780]in biomass production
[00:46:05.060]between years.
[00:46:05.860]So what I would like to highlight
[00:46:08.220]here is that
[00:46:09.220]cover crops planted
[00:46:11.080]on similar dates
[00:46:13.080]in consecutive years,
[00:46:14.260]they did not yield similar biomass.
[00:46:16.360]So it is because
[00:46:17.860]there was year to year variability
[00:46:20.180]in weather conditions.
[00:46:21.160]So
[00:46:22.820]this also highlights that
[00:46:24.260]you should never
[00:46:26.660]expect the same amount of biomass every year.
[00:46:29.120]So these are
[00:46:32.800]some of the photos from fall
[00:46:34.720]planted rye in Scoss Bluff,
[00:46:36.700]Nebraska for the 2023 to
[00:46:38.620]2024 growing season.
[00:46:39.920]And I choose rye because it is
[00:46:42.740]a common cover crop in this region.
[00:46:44.380]So the purpose of
[00:46:46.800]this picture is to show how
[00:46:48.900]visual appearance or
[00:46:50.740]visual assessment can provide
[00:46:52.800]quick biomass estimates in the field
[00:46:54.980]without destructive sampling.
[00:46:56.560]So what we did, we
[00:46:59.000]clipped above ground samples in a
[00:47:00.880]two feet by one feet quadrant.
[00:47:02.400]They were dried and measured biomass
[00:47:04.820]in kg per hectare.
[00:47:06.020]So across these photos,
[00:47:09.180]you can see
[00:47:10.880]plant height and plant density
[00:47:12.760]or canopy coverage differ among
[00:47:14.840]photos. So I would like to
[00:47:16.840]draw your attention here
[00:47:19.040]to the fact that
[00:47:20.240]plant height and density can
[00:47:22.780]tell the story of biomass estimates.
[00:47:25.060]For example,
[00:47:25.900]left photo, the photos
[00:47:28.860]on the left, so it has 25%
[00:47:30.800]ground cover. So you can see there is
[00:47:32.580]sparse vegetation with
[00:47:34.260]lot of visible gaps.
[00:47:36.240]Whereas in the middle photo,
[00:47:38.160]it has 66% ground cover
[00:47:40.960]and photos on the right
[00:47:42.840]with Yankee rye, so it
[00:47:44.840]has 90% ground cover.
[00:47:46.600]It has very thick growth
[00:47:48.900]and there are no any visible
[00:47:50.380]there is no any visible gaps.
[00:47:52.760]So, but you can see
[00:47:54.760]the differences in biomass produced.
[00:47:57.240]So the message I want to deliver here
[00:48:00.440]is that taller plants
[00:48:02.340]with higher ground coverage,
[00:48:03.940]they can typically result
[00:48:05.400]in more biomass yield.
[00:48:06.980]So similarly here,
[00:48:10.880]so the two photos for the Albon rye,
[00:48:13.940]so they have similar height, right?
[00:48:16.280]So 99 centimeter and 97 centimeter.
[00:48:19.260]So they have similar height,
[00:48:20.860]but they differ in ground cover.
[00:48:22.740]You can see one has 88% and another has 93%.
[00:48:27.300]So the message here I would like to emphasize is
[00:48:31.120]higher cover can result in higher biomass yield.
[00:48:34.820]And there is another photo for hairyweeds.
[00:48:38.760]So here I would like to stress that
[00:48:41.560]different cover crop families like legumes versus grasses
[00:48:45.060]can produce different biomass
[00:48:47.260]even if ground coverage looks similar.
[00:48:50.840]So it can vary between
[00:48:52.720]plant families too.
[00:48:56.080]So I'm giving a summary of the research evidences
[00:48:59.460]that I taught.
[00:49:00.580]So the cover crop planted by mid-September
[00:49:04.240]produced 10 times more biomass
[00:49:06.260]than those planted in late October
[00:49:08.180]with termination occurring in mid-April.
[00:49:11.400]So if you delay spring cover crop termination
[00:49:14.120]from early to late April,
[00:49:15.960]they increase biomass production by four times
[00:49:19.380]for cover crops planted in early October.
[00:49:22.700]And a warm, wet growing season can produce
[00:49:25.220]four times more biomass compared to a cool, dry season.
[00:49:28.840]And biomass production range from 110 to 6,710 kg per hectare
[00:49:33.840]for wheat, 190 to 6,310 kg per hectare for rye,
[00:49:40.340]750 to 7,160 kg per hectare for tritical,
[00:49:43.900]and 100 to 2,200 kg per hectare for canola.
[00:49:48.440]And if you extend growing periods,
[00:49:50.880]particularly from mid-September
[00:49:52.680]and terminate it late in early May in the spring,
[00:49:56.920]that can produce greater biomass by 158% for wheat,
[00:50:01.200]112% for rye, and 131% for tritical,
[00:50:06.460]and 247% for canola compared to shorter growing intervals,
[00:50:11.060]which is basically planting in early October
[00:50:13.620]and terminating in mid-April.
[00:50:15.540]So the key take-home message from this presentation today
[00:50:20.580]is that year to year,
[00:50:22.660]weather variability can affect biomass yields,
[00:50:25.420]even with cover crop planted on similar dates.
[00:50:28.480]And setting realistic biomass goal is essential,
[00:50:31.980]especially considering the harsh winter conditions
[00:50:34.680]that can limit productivity.
[00:50:36.540]And if you adjust your planting and termination timing,
[00:50:40.100]focusing on extended growing interval,
[00:50:43.140]that can help to maximize biomass yields
[00:50:45.500]under diverse environmental conditions in Nebraska.
[00:50:49.140]So with this, I would like to wrap up
[00:50:52.640]my talk here.
[00:50:54.400]So and then we will move to breakout rooms discussion.

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Cover Crop Biomass Expectations

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