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Interseeded Cover Crops Results
Studies such as this will be shared by area farmers starting this week at On-Farm Research Updates (Feb. 15 at Holthus Conv. Center in York)! RSVP at: go.unl.edu/2023ofr. Since 2019, a group of area farmers have been interseeding cover crops into early season corn (V3-V4) and soybean (VE-V2). The goals for interseeding cover crops into cash crops include: providing nutrients for the cash crop, weed control, erosion control, diversity, reducing inputs such as fertilizer and chemicals, and providing forage for grazing after harvest. Interseeding of cover crops can also occur at other growth stages, such as at male row destruction in seed corn or at senescence in late-season corn and soybean. This article will focus on our results from early-season interseeding of cover crops into corn and soybean.
In 2019, two farmers interseeded cover crops (one drill interseeded and one broadcast) into corn in York and Seward counties. Both got establishment and showed no yield differences between interseeded and check. In 2020, a partnership formed between The Nature Conservancy, Upper Big Blue NRD, Extension, Kelloggs and area farmers. A four row interseeder was purchased. Six farmers chose to conduct studies via on-farm research where they maintained the same field-scale strips of interseeded cover crops and check treatments for 3 years. The different cover crop mixes and rates can be viewed at jenreesources.com.
From 2020-2022, fields were impacted by July 9, 2020 and 2021 wind events and June 14, 2022 hail. We had 12 site-years of corn studies and 2 site-years of soybean studies. Biomass samples of the cover crops and also weeds were taken each September. Cover crop biomass ranged from 200 lb/ac to 4 tons/ac depending on the location, hybrid, irrigation, and storm events. In 10 of 12 site-years, interseeded cover crop had more biomass than the check treatment (weeds).
Yield: No corn yield difference between check and interseeded in 6 of the 12 site-years. Yield losses ranged from 2-10 bu/ac in the remainder. No soy yield difference between the interseeded and check.
Net Return: In 10 of the 12 corn site-years, and 1 of the soybean site-years, the check treatment had a higher net return. (However, no benefit to grazing, reduced inputs, etc. was given to interseeding).
Soil Health Values (PLFA & Haney): Large numerical increases in soil health numbers when all 6 sites were combined (as well as some individual sites). Significant increase in the Check from 2020 to 2022. Significant increase in the Interseeded from 2020-2022. However, because this happened for both treatments, when comparing Check vs. Interseeded from 2020 vs. 2022, there is no difference. Why? All farmers were incorporating additional soil health practices across their entire fields (planting rye each fall, grazing, adding biological products, etc.) that would have impacted both cover crop and check treatments. Good news: all increased their overall soil health (soil microbial pops and scores) in 3 years.
Soil Nutrient Values: There were no differences between OM, pH, P, S, K, and base saturations between Check and Interseeded from 2020 to 2022 across sites. Numerical changes occurred at individual sites.
Our studies proved that drill interseeding of cover crops into early season corn and soybeans can be achieved for establishment that lasted after harvest with regrowth of perennial covers into the spring. We also showed this in spite of a number of PRE- herbicides used. We increased beneficial insects and saw pest insects feeding on cover crop instead of cash crop. We increased diversity in the fields and had additional cover aiding erosion control. We also showed reduced water use in the corn where the diverse cover crop was used compared to the check treatment. The disappointment to me was the low amount of forage for those desiring to graze after harvest and the spotty survival of perennials in the spring. However, those who grazed said there was value in the amount of green material present at harvest coupled with the corn residue. Additional challenges can include the fact that it does look ‘messy’, one needs to think through herbicide options ahead of time, and we need to put dollars to additional benefits that are harder to calculate (soil erosion, etc). Next week I’ll share our next steps in where we’re headed.
JenREES 6/5/22
This past week was beautiful! We saw more recovery on frost-damaged plants and it allowed for a lot of post-herbicide spraying. A question I kept receiving was how long to wait to spray crops that were frost damaged. Some labels will say to wait 48-72 hours before applying a herbicide while others don’t give a time, they just mention that injury to the crop can occur under specific temperatures or when plants are under stress. How I answered based on what we have recommended in the past is for any type of adverse weather event impacting crops (hail, frost, etc.), wait at least 3-5 days based on the label or until one starts to see plant regrowth of both the crop and the weeds. We would say the same for anyone who unfortunately experienced hail damage this weekend.
Interseeded Cover Crops: This past week was also a busy one for our team interseeding cover crops into V3-V4 corn. We are currently in the third year of a partnership between our farmer cooperators, The Nature Conservancy, Nebraska Extension, UBBNRD, and Kellogg’s. A couple cooperators are in the 4th year. The goals for planting cover crops into early season corn and soybean include reducing nitrogen inputs, weed control, improving soil health, increasing diversity, and providing forage for livestock. We’ve successfully achieved cover crop establishment and season long growth, covers that survived after harvest and survived into the spring to various extents in all years of the study. In the on-farm research locations from 2019-2021, the interseeded cover crop yielded less in 5 of the 12 site-years but yield was not impacted in the others. In 2021, there was no yield difference between the interseeded cover crop and check strips when seeded into soybean at two locations. Yields in 2020 and 2021 were impacted in some fields due to the July 9th windstorm in both years which opened up the canopy producing greater cover crop biomass.
Biomass samples taken in late September pre-harvest and pre-frost has ranged from 97 lb/ac to 2192 lb/ac. These are field averages as individual reps were over 4000 lb/ac in severely wind damaged fields. Additional growth was achieved after harvest but not collected. Biomass samples for nitrogen content taken in 2021 ranged from 5-200 lb N /ac. Beginning soil health assessments were taken the first year of the study and will be completed in September of 2022 for comparison.
We’ve also learned a lot about herbicide interactions with cover crops; they are fairly resilient. For the corn locations, we’ve went with a full PRE herbicide (generic Lexar, Callisto, Acuron…have not used Resicore) and then for POST, within 3 days either direction of interseeding using Roundup, Liberty, and sometimes dicamba with no impacts to the covers that we interseed. We have also had success using ½ rate of Lexar or Callisto at least 1.5 weeks prior to interseeding. The covers were scraggly, but they did come through it. We have never used a residual on the corn we interseed, but using a Group 15 was an option once the covers emerged and got up about an inch to provide residual if the guys wanted it.
For the soybeans, if a full PRE was applied at least 3 weeks prior to interseeding, we didn’t worry about it (which was the case in 2021). For POST, we just used Roundup and either Liberty or Dicamba within 3 days either direction of interseeding with again, the thought of a Group 15 if needed for residual once the covers were 1″ tall. In soybean, we interseeded 10 lb/ac red clover with 20 lb/ac of wheat. The field we interseeded at emergence had red clover survive the entire growing season, through harvest, and was growing this spring for the successive corn crop. It was unexpected and gave us insight into another way of potentially establishing a perennial crop for nitrogen. It ended up being killed out by the corn herbicide, but is something we’re repeating in different ways in 2022.
Regarding species that we feel are most successful in the corn, we like buckwheat, iron and clay cowpeas, clovers (red and sweet), brassicas such as collards and radishes, forage soybean, annual and Italian ryegrass. We’ve consistently seen sweetclover and the ryegrasses survive the winter into the spring. Depending on the year, we’ve also seen red clover and hairy vetch survive the winter. We’ve learned much more that I don’t have room for here. If you’re interested in learning more, be watching for our articles at cropwatch.unl.edu. Also, save June 30th for a potential Interseeding Cover Crop Driving Tour.
JenREES 5/9/21
Hopefully the rains were a blessing in helping the crops where crusting was a concern, adding moisture to the seedbed, and in activating herbicide. This article reaches people throughout the State, so with some experiencing frost potential as I write this, if rhubarb leaves are not damaged too much by frost and the stalks remain firm, it is still safe to eat. If the leaves are severely damaged or the stalks become soft or mushy, do not eat these stalks. Remove and discard them. New stalks can be harvested and eaten. Rhubarb often develops seedheads following cold temperatures, but this also does not affect eating quality of the stalks. Remove rhubarb seedheads and discard.
This week will share on the results we obtained from on-farm research studies where cover crops were interseeded into corn. In 2019, there were two locations in York and Seward counties (interseeded at V5-V6). In 2020, 6 of 11 locations were conducted via on-farm research in York, Seward, Clay, and Hamilton counties (interseeded at V4). Four of the six locations compared an interseeded cover crop to a check treatment of no cover crop. One location compared two corn populations (27,000 vs. 31,000 seeds/ac) to determine corn yield and cover crop biomass impacts. One location compared using only the middle drill unit to interseed the cover crop vs. using all three drill units between the rows to determine any differences in cover crop biomass.
2019 Results: In 2019, the cover crop at the Seward county location emerged and then died, we hypothesize, due to reactivation of Group 27 herbicide. Thus, no biomass samples were taken. At the York county location, cover crop biomass sampled prior to the first hard freeze ranged from 97-220 lbs/ac. It was good to see successful establishment at both locations and that cover crop growth occurred at one of them. In 2019, there were no yield differences between the corn in the check treatments (241 and 258 bu/ac) vs. cover crop interseeded treatments (241 (N mix), 243 (diversity mix), and 256 bu/ac) at the York and Seward locations respectively, which was also encouraging. Net return was less for the interseeded cover crop treatments vs. the check.
2020 Results: In 2020, cover crops emerged at all locations and grew throughout the season. Cover crop biomass varied by location with the most occurring in fields that were damaged by the July 9, 2020 windstorm (the location with the greatest biomass had 45% green snap). Thus, the open canopy resulted in greater weed and cover crop biomass. Biomass samples were collected in late September by taking three 30” X 30” or 36 X 36” squares for each treatment (dependent upon row spacing). The samples were sorted in the field into weeds, interseeded forbs/legumes, and interseeded grasses and placed in separate paper bags. Samples were weighed and dried. We wanted to compare any differences in weed biomass between the check and interseeded treatments, especially since no residual herbicides were used in 2020. There were no differences in weed biomass between the check and interseeded cover crop treatments. Total cover crop biomass accumulated varied by site and ranged from 277 lb/ac to 3818 lb/ac. It should be noted that the cover crops continued to grow after we sampled until the first hard freeze occurred. The cowpeas provided the greatest biomass and grew to the tops of the tassels. They also formed a ‘bridge’ between corn rows where the canopy broke open. Cowpeas, hairy vetch, sweetclover, and forage soybean were all fixing nitrogen during the 2020 growing season. The red clover and hairy vetch that survived the winter were fixing nitrogen in the spring of 2021.
The windstorm greatly impacted yields as well. Across all the sites, corn yield for the check averaged 214 bu/ac while corn yield for the interseeded treatment yielded 209 bu/ac. At four of the six sites, yield was significantly lower where the cover crop was interseeded. At the remaining two sites yield was not different between treatments. Net return for the corn where the cover crop was interseeded was less at five of the six locations. Net return includes the yield and price of the corn crop and cost of cover crop seed and application. Other than the York county location (two years), all the location data is based on one year of research. These studies will continue in the same fields and strips for at least three years, so it will be interesting to watch for any changes in soil biological and physical properties over time as well. Visually, in the field where the center drill unit vs. 3 was used, it appeared that the 1 drill unit had more biomass. Statistically, it ended up the same as the three drill units for total cover crop biomass. At the York location where cover crops were interseeded into two corn populations, there were no yield differences between the corn populations; however, both yielded less than the check treatment. A special thanks to all the growers working with us on these interseeding cover crop studies and to The Nature Conservancy, Upper Big Blue NRD, NRCS, and Kellogg’s for their partnership with Nebraska Extension on this effort. If you’d like more information, I’ve provided tables of data and links to videos we produced at my blog site jenreesources.com.
0.5 lb/ac chicory) interseeded at V5-V6 corn vs. check treatment.
Seward County (right), a Hagie was used to broadcast interseed 10 lb/ac red clover and 5 lb/ac buckwheat into V6 corn vs. check treatment.
* denotes statistically significant at 90% confidence level.
Cover crop biomass as a result of interseeding using three drill units (left) vs. only the center drill unit (middle). Close up of Penn State Interseeder drill units (right).
Nebraska On-Farm Research Virtual Field Day Interseeding Videos:
- Interseeding drills: https://cropwatch.unl.edu/interseeding-cover-crops-steve-melvin-june-12-2020
- Interseeding into Soybean: https://cropwatch.unl.edu/interseeding-cover-crops-soybeans-steve-melvin-june-10-2020
- Interseeding studies: https://youtu.be/gQKAGzkweG4
- Interseeding Mixes: https://youtu.be/b64PCMV1pwc
- Interseeding and Herbicide programs: https://youtu.be/5P8tE3oQ7hA
JenREES 5/2/21
With the challenge of growing cover crops, particularly after corn harvest, interest in interseeding cover crops into living corn and soybean has increased in recent years. Goals for doing so include using the cover to: grow nitrogen for the crop, remove excess nitrogen (in the case of seed corn), aid in weed and erosion control, increase biodiversity, determine any soil health benefits, and desire for fall biomass for grazing. Some are also concerned about increasing regulation and wanting to figure things out ahead of the curve. Planning is key when it comes to interseeding cover crop into corn or soybean. Planning needs to include the goal of why interseed, the cover crop species interseeded, how the cover will be interseeded, the corn/soybean crop development stage for interseeding, and the herbicide program used.
A few years ago, we wrote an article sharing what was known about interseeding cover crops. The following is information we’ve learned as an interseeding project between The Nature Conservancy, Upper Big Blue NRD, Nebraska Extension, 11 farmers, NRCS, and Kellogg’s.
Timing: In corn, we’d recommend aiming for V4 (four leaf collars). V5-V6 is almost too late in years where canopy closure occurs quickly. The literature says there’s no yield loss after V2. For soybean, aerial interseeding around senescence (leaves turning yellow) is one option. From plots interseeded at V4 in 2020, we felt that was almost too late for aiding establishment. This year we will be trying at planting through V2.
Species: Penn State has a mix that’s considered the interseeding standard; it includes annual ryegrass, red clover, and hairy vetch. From the 12 species mixes we tried, the annual ryegrass, vetch, red clover all survived and were growing this spring. Thus, most likely why it’s considered the standard.
In corn, we’ve tried multispecies mixes because of the growers’ and partners’ goals and testing what came through different herbicide programs. We found the first species to emerge were the buckwheat and cowpeas. The farmers liked the species that provided more of an understory like the annual and Italian ryegrass, collards and other brassicas, and buckwheat. Cowpeas grew up to the corn tassels and provided the greatest biomass. Most of the species went to seed. Cowpeas, forage soybeans, and sweet clover were fixing nitrogen in season.
For diversity, the flax and buckwheat upon flowering drew many beneficial insects to the field. Pests like grasshoppers ate the covers in the interseeded strips and left the corn alone from what I observed.
In soybean, wheat was planted in the soybean management field day trials last year with some success. This year we’re considering wheat + red clover for the fields that will be interseeded from planting through V2.
Herbicide Programs: This is the difficult part. I think ideally (and I’m unsure if this is even realistic yet), a cover between rows aiding in weed control, adding nitrogen, providing fall biomass, and regrowing the following spring to aid in weed control again with only needing to add herbicide in a band, would be pretty cool.
In the wet year of 2019, Callisto-type (Group 27) products did their job and kept re-activating. This led to covers dying in one field. So in 2020, I suggested no residuals in post- apps. The guys went with me on this with most doing a pre- with residual followed by a post- of only glyphosate or Liberty prior to interseeding. The July 9th, 2020 windstorm causing plants to greensnap and/or bend caused problems with the canopy opening up and weed control in addition to biomass growth became a problem in these fields in competing with the corn crop. I was just sick about this and the guys extended much grace to me.
This year, for corn, some guys are sticking with last year’s program because it worked well for them, particularly in no-till with heavy residue. Another thing some may try is to apply a pre- with residual, interseed at V4 and then upon 1-2” growth of the covers, apply Dual II Magnum or Outlook (no grazing restriction with Outlook) to provide residual to aid in weed suppression. One farmer who applied generic Lexar pre-plant in some fields and did split app in others in 2020, still saw cover crop growth and emergence from the split applied. The cover crop growth in the split-applied was just stunted and thin compared to the fields where he applied the full rate pre-. He’s testing herbicide programs this year.
For soybean, there’s even more risk. For those who wish to plant and interseed at the same time, we’re trying a burndown immediately prior to interseeding (if they hadn’t applied an early pre- already), allowing the cover to get 1-2” tall and then go with a Group 15 chemistry. The other option we’re trying is going with their pre- with residual followed by interseeding at V2 and application of Group 15 herbicide after cover reaches 1-2” of growth. We also have guys who are planting soybean green into rye and will try interseeding after rye termination. We have no idea how all this will work and if others have ideas, please feel free to share! Next week I’ll share the yield and biomass results from the past few years.
The above pics were post-harvest. The covers showed good at that time still but they seemed to disappear pretty fast upon more hard frosts.
The above pictures were taken in March 2021 of spring growth. Annual ryegrass, hairy vetch, red clover, and collards survived the winter. As time went on, one could easily ‘row’ where the covers were interseeded in June 2020. The taproots on the red clover were extra impressive to me! Also, pretty much always saw earthworms when I dug up one of these plants.
JenREES 5-26-19
Driving through Nebraska towns around Memorial Day, I find the streets lined with flags such a beautiful site. Grateful to live in our Country with our freedoms. I’m also grateful for those who paid the ultimate price for our freedom and for their families left behind.
Flooding/Ponding and Crop Effects: With the rain, some may be experiencing ponding/flooding of crops. Emerged corn prior to 6 leaves can survive from two to four days depending on temperatures and if entire plants are submerged or not. Cooler air temperatures (60’s and cooler) allows for longer survival than temperatures in the mid-70’s and warmer. Little data exists for germinated seeds and seedlings prior to emergence, but they most likely would experience soil oxygen depletion within 48 hours. Once emerged, soybean may handle a fair amount of flooding due to the growing point being above ground (depending on if they’re submerged or not). Four or more days of flooding may result in shorter plants due to shorter internodes and/or perhaps fewer nodes. Stand reductions may be observed after seven days of flooding (depending on size and if completely submerged or not).
Prevent plant may be another topic on some growers’ minds in addition to considerations after the May 25 corn planting date for crop insurance. These are addressed in this week’s CropWatch at http://cropwatch.unl.edu.
Interseeding Cover Crops: In a previous news column, I touched on the topic of interseeding cover crops into corn or soybean. For this week’s CropWatch at http://cropwatch.unl.edu, we provide more information based on the research available. For those considering this as an on-farm research study, please contact me or your local Extension Educator soon to work out details.
Wheat: Michael Sindelar and I looked at wheat in Clay and Nuckolls counties last week. For diseases we’re mostly seeing powdery mildew and septoria leaf blotch. Backlighting revealing yellow specks on upper leaves in some fields will most likely develop into leaf rust. Wheat ranges from nearing flag leaf to beginning flowering. My concern for wheat in the heading to flowering stage is risk of fusarium head blight (scab) with the rain we’ve been receiving at heading/flowering. The scab risk tool (http://www.wheatscab.psu.edu/) is showing a low to medium risk for our part of the State right now. If you do consider a fungicide, your best options include Prosaro, Caramba, or Miravis Ace as these products will help protect against scab in addition to kill any fungal diseases on your wheat leaves. Other products are off-label once flowering begins or are not as effective preventing scab based on research. Best application timing to prevent scab is when 30% of the plants in the field are at 15% flowering (early flowering stages).
Lawn Care: I know some are getting tired of mowing already! Just a reminder to keep mowing heights at 3″. Spring is an important time for deeper root establishment before the summer heat sets in and maintaining a higher lawn height allows the grass to develop that root system. I’m seeing several lawns being scalped in an effort to reduce amount of mowing. Mowing too short stresses the grass impacting its ability to set deeper roots for later. It will also allow for more weeds to germinate in the lawn.
JenREES 5-12-19
Crop Update: It is really nice to see crops emerging! The corn, soybean and wheat I 
looked at didn’t seem too impacted by the frost. There may be places where crops were more affected. For corn and wheat, it’s important to look at the growing point and make sure it’s white/yellow and firm and not discolored and soft. Impacts to wheat later on can also be seen at heading in white awns. Soybean are more susceptible to frost when those hypocotyls are just emerged at soil level or above and exposed when frost occurs. Soybean with hypocotyls that are pinched and brown will probably not survive. Soybean that have light scarring of hypocotyls and cotyledons most likely will survive. Look for the plumule (first true leaves from the shoot) within 7 days post-frost to ensure the growing point wasn’t injured. (You can see the plumule between the cotyledons in the upper right-hand picture below).
Hopefully we don’t have to deal much with replanting. As we assess stands, this week’s UNL CropWatch at http://cropwatch.unl.edu has an article regarding stand and replant considerations for corn. It’s important to take stand counts in several areas of the field. There’s a table on the CropWatch website which shows original planted stands with planting date and what can be expected for potential yields based on stand counts and replanting at a later date. Roger Elmore shared the following example, “If the original planting date was April 30, a population of 35,000 plants/acre is expected to provide maximum yield. If the population is only 20,000 plants/acre, yield potential is 89% of the maximum for the April 30 planting date. If several 4- to 6-foot gaps occur within the row, yields will be reduced an additional 5% relative to a uniform stand. Stand gaps of 16 to 33 inches will only reduce yield by 2%. Estimate replant yield with Table 2. Use planting date and target plant population to estimate the yield potential of the replanted field. Replanting on May 20 at 35,000 plants/acre will result in approximately 87% of the maximum yield. Compare the replanted crop to the original crop which was planted on April 30 that now has a population of 20,000 plants/acre, and consider the costs of replanting. Expected yields are 89% for retaining the old stand versus 87% for a replant. Remember though, there is no guarantee of getting a good stand with replanting. Insect and disease pressure may be greater in replanted fields.” You may also be interested in checking out a new CropWatch podcast on corn seedling diseases at: https://go.unl.edu/a5zf.
Interseeding Cover Crops: The past four years, some growers have shared with me an interest in interseeding cover crops into corn or soybean. The growers have different goals which may include fall grazing, additional nitrogen from the cover, or soil health impacts such as increasing soil organic matter. Because cover crop establishment after corn and soybean is more difficult and inconsistent year to year, there’s been an increasing interest in interseeding. Basically, the thought is to plant the cover before the corn or soybean crop reaches canopy closure. The cover emerges and then essentially doesn’t grow much during the growing season due to minimal light interception. After harvest, the hope is the cover has greater biomass production since it’s already established. Research in general from other states hasn’t shown yield reduction in corn when the cover was planted after V4…typically from V5-V7. When the cover was interseeded earlier, some states have found yield reductions as the cover basically competes like a weed with the corn for resources. A question we often receive is regarding herbicides. Wisconsin shares that Sharpen and Resolve for herbicides allowed for greater success with short half-life. They planted radish, oat, pea, rye, red clover in their trials. A family conducting on-farm research in Merrick County has been interseeding the past three years. In their 2018 trial, they used 32 oz glyphosate + 5 oz Status per acre post on 6/1/18 (planting date 5/17/18). They interseeded on 6/26/18 with 6 lb cowpea, 6 lb soybean, 0.5 lb crimson clover, 5 lb sunhemp, 2 lb hairy vetch, 3 lb buckwheat, 0.5 lb chicory, 0.5 lb flax, 0.5 lb rapeseed/canola, 6 lb Elbon cereal rye, 6 lb spring oats per acre. From conversation they were happy with cover emergence after Status application but I failed to ask which species looked the best. They will continue the study for several years. Outside of this, we have very little research from Nebraska and my hope is to obtain more research via on-farm research this year! We’ve created a 2 treatment and 3 treatment protocol which can be found at: https://go.unl.edu/kvjf. The three treatment protocol can be altered a number of ways: including looking at 2 different mixes compared to a check, looking at different ways of seeding the cover crop vs. check, and looking at different interseeding timings vs. check. Please contact me if you’re interested in trying this!
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