Weed Suppression by Grazed Winter Cover Crops with Varied Timing of Livestock Removal

Final report for GNC21-339

Project Type: Graduate Student
Funds awarded in 2021: $14,839.00
Projected End Date: 05/31/2023
Grant Recipient: Kansas State University
Region: North Central
State: Kansas
Graduate Student:
Faculty Advisor:
Dr. Sarah Lancaster
Kansas State University
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Project Information


As resistant populations of weed species in Kansas continue to rise, there is a need to implement integrated weed management practices. Cover crops are known to suppress weed growth with the large amounts of biomass produced, the key factor that influences weed suppression. The proposed project will produce quantitative datpertaining to the level of weed suppression in fields where winter cover crops are grazed with cattle. This research project will take place in Eastern Kansas and focus on cereal rye. Since the relationship between cover crop biomass and weed suppression is observed throughout the region, data will be applicable to farmers across the North Central Region. 

Before cattle enter the field, four paneled exclosures will be established to restrict cattle grazing. These restricted areas will be made of three panels (each 8ft long) that are fashioned in a triangle. Additional areas will be restricted at two-week intervals to collect data to determine if there is an effect on weed suppression due to timing of livestock removal from the field. Biomass will be collected each time exclosures are placed in the field. Once biomass is removed, it will be sorted and weighed to determine the differences between weed suppression and cover crop biomass production with different timings.  

 This data helps farmers make educated management decisions when it comes to the removal of grazing cattle off of winter cover cropsEducated management decisions early in the growing season will offeeconomic gain by balancing weed management costs later in the growing season with the value of beef production realized in the late winter and early spring. The outcomes of this project will be data-based recommendations on when to remove cattle from grazing cover crop biomass. This will in turn have both direct and indirect effects that will reduce weed populations, herbicide resistance, and overall herbicide applications. Through these outcomes, producer profitability will be increased as well as stewardship of the environment through profitable use of integrated weed management strategies. 


Project Objectives:

The proposed project will provide a number of learning and action outcomes that revolve around profitabilitystewardship, and quality of lifeWith regard to learning outcomes, farmers and ranchers will increase profitability by learning when to remove cattle grazing cover crops to maximize weed suppressionIn regard to action outcomes, farmers and ranchers will improve environmental quality and stewardship by optimizing non-chemical weed control methods. An indirect effect that is anticipated is a decreased opportunity for herbicide runoff into the environment as well as reduce the amount of herbicide resistant weed populations in these areas. 

The anticipated audience for the data are farmers utilizing winter cover crops who either graze their cattle or allow ranchers to graze cattle on cover crops. The farmers and ranchers whose operations are utilized and impacted directly by the project will be located in Kansas; however, the data will be applicable to growers throughout the North Central Region. Outcomes will be measured by surveying how likely a farmer or rancher who attends the field day demonstrations will be to take into consideration and adopt the recommendations provided. Additionally, extension specialists and educators will be surveyed to determine if producers in their district will be likely to adapt to recommendations and data provided to them. 


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Materials and methods:

Five research locations were selected in eastern and central areas of Kansas. These were on-farm locations planted to cover crops between August and September of 2021 and were to be grazed by cattle. Each location had unique management parameters including cover crop species mix, cattle type, stocking rate, field size, and grazing period length. The common parameter was that each cover crop mix had a dominant grass cover crop species such as cereal rye or triticale. Cropping and management history of each field likely affected weed species and biomass recorded.  We chose not to disrupt farmer practices to ensure participants. 

Wabaunsee, Kansas

The field in Wabaunsee, KS was a no-tillage field in the north-eastern area of the state. This field was in a corn-soybean rotation, and just prior to this research silage corn was harvested. Soil tests registered organic matter at 3% with a pH of 5.4. The cover crop mix of cereal rye, spring barley, radish, and spring pea was drilled after silage harvest on September 11, 2021. No irrigation was utilized at this location, and the field was considered dryland crop production. Predominant weed species as noted by the farmer were giant foxtail (Setaria faberi Herrm.) and Palmer amaranth (Amaranthus palmeri S. Watson). Cattle at this location consisted of 80 Angus heifers that weighed an estimated 454 kg and had access to 41 ha of pasture to graze (1.95 AU ha -1). Grazing occurred for 92 non-consecutive days between December 5, 2021 and April 16, 2022. Cattle were provided hay when available cover crop biomass was low due to grazing or snow cover.

Castleton, Kansas

The field in Castleton, KS was a no-tillage field in the south-central area of the state. This field was in an annual forage rotation, and prior to this research was an annual summer forage and recurring crabgrass which was grazed in the late summer-fall. The cover crop mix of triticale, winter pea, and turnip was drilled on October 1, 2021. No irrigation was utilized at this location, and the field was considered dryland crop production. Predominant weed species at this location were horseweed (Erigeron canadensis L.), common chickweed (Stellaria media (L.) Vill.), henbit (Lamium amplexicaule L.), green flower pepperweed (Lepidium densiflorum Schrad.), prickly lettuce (Lactuca serriola L.), Carolina geranium (Geranium carolinianum L.), evening primrose (Oenothera biennis L.), yarrow (Achillea millefolium L.), pinnate tansy mustard (Descurainia pinnata (Walter) Britton) and flixweed (Descurainia sophia (L.) Webb ex Prantl). Cattle consisted of 546 red Angus calves that weighed an estimated 227 kg and had access to 78 ha of pasture to graze (3.5 AU ha -1). Grazing occurred for 32 consecutive days between January 3 and February 1, 2022. Cattle were provided hay when available biomass was low due to grazing or snow cover.

Ellsworth, Kansas

The field in Ellsworth, KS was a no-tillage field in the south-central area of the state. Prior to this research grain sorghum was grown in 2021. The cover crop mix of cereal rye, radish, and turnip was interseeded into the grain sorghum crop on September 7, 2021. The field has a center pivot, but the cover crop did not receive any irrigation. Predominant weed species at this location were henbit and common chickweed. Cattle type consisted of 118 commercial crossbreed calves that weighed an estimated 305 kg and had access to 116 ha of pasture to graze (0.68 AU ha-1). Grazing occurred for 68 consecutive days between November 11, 2021 and January 18, 2022. Cattle were provided hay when available biomass was low due to grazing or snow cover.

Clay Center, Kansas

The field in Clay Center, KS was a no-tillage field in the north-central area of the state. Prior to this research corn was grown in 2021. The cover crop mix of cereal rye, radish, forage collars, and turnip were interseeded into the corn crop on August 26, 2021. The field has a center pivot but the cover crop did not receive any irrigation. Predominant weed species at this location were chickweed and henbit. Cattle consisted of 75 commercial cows that weighed an estimated 545 kg and had access to 135 ha of pasture to graze (0.67 AU ha-1). Grazing occurred for 62 consecutive days between January 29 and April 1, 2022. Cattle were supplemented feedstuff when available biomass was low due to grazing or snow cover.

Topeka, Kansas

The field in Topeka, KS was a no-tillage field in the north-eastern area of Kansas. Prior to this research corn was grown in 2021. The cover crop mix of cereal rye, radish, and crimson clover was drilled after corn harvest on September 29, 2021. The field has a center pivot, but the cover crop did not receive any irrigation. Predominant weed species at this location were chickweed, henbit, and horseweed. Cattle consisted of 139 commercial calves that weighed an estimated 227 kg and had access to 38 ha of pasture to graze (1.83 AU ha-1). Grazing occurred for 106 consecutive days between December 19, 2021 and April 4, 2022. Cattle were supplemented feedstuff when available biomass was low due to grazing or snow cover.

 Experimental Design

A randomized complete block design with four replications was used at each experimental location. Each site was unique to the number of treatments it received and what each of those treatments was. At each location, treatment was grazing days and was unique based on weather conditions and farm management at respective sites. Measurements were taken of both weeds and cover crop biomass present. During the grazing period, exclusion cages were placed in the field to restrict the grazing of cattle from 0.75 m2 area. This area simulated the removal of grazing from the entire field. Four replications were placed at each simulated removal timing to ensure variability was captured across the field. These four replications were placed with geographic regard to the water source (Figure 3.2). Grazing is inevitably higher near the water source, so replications were placed to ensure that variability was accounted for at each site.

 Data collection:

At all locations before grazing, during grazing, and prior to cover crop termination (or planting) cover crop biomass, cover crop height, weed biomass, forage quality, and weed height were measured. These values were measured to understand the relationship between stocking rate, cover crop biomass, cover crop height, and weed biomass.

Cover crop and weed heights were assessed by measuring three representative plants with a ruler and reporting the mean. Cover crop and weed biomass were measured by clipping and removing all biomass above ground level within 0.1 m2 and recording wet weights. Wet biomass was then placed in a dryer until constant dry weight was recorded.

Forage quality was assessed by hand plucking samples outside of cages in the field to resemble biomass removal habits of cattle (enough to fill a 1 liter plastic bag). These samples were dried at 48°C until constant dry weight and then sent to Ward Laboratories Inc. in Kearney, NE for near infrared spectroscopy analysis. Values analyzed were CP, ADF, NDF, NDFD, IVDMD, RFV, and RFQ. These values were determined to estimate the economic value of cover crop as feed inKansas. These feed values all play an important role in cattle nutrition and production (Lalman 2017; Lemus 2020).

 Statistical Analysis:

All data were analyzed using the software “R” (R Core Team 2021). All assumptions of normality were evaluated with box plots, residuals, and quantile-quantile plots using R package ggplot2 and ggthemes (Wickham 2016; Arnold 2021). Data were subjected to an analysis of variance in R using a linear mixed model using package lme4 and lmerTest (α = 0.05) (Kuznetsova, Brockhoff, Christensen 2017). Replication was considered a random effect. Means were separated using Tukeys HSD Test (α = 0.05) with R package emmeans, multcomp, and multcompView (Hothorn, Bretz, and Westfall 2008; Graves, Piepho, and Selzer 2019; Lenth 2022).

Research results and discussion:

LilyAnneWoitaszewski2023 Across all locations, three locations provided adequate data to analyze and report results. One location, Clay Center, had high wind and lack of moisture which resulted in corn residue filling paneled areas. Despite attempts to remove residue, weed emergence was affected and none was observed within treatment areas. At another location, Ellsworth, an extremely low stocking rate, under 0.68 AU/ha-1, and treatment locations were not placed in primary grazing locations. This resulted in lack of consistent grazing and data was not presumed reliable.

At Castleton, Topeka, and Wabaunsee, results varied by weed species type and life cycle. Both Castleton and Topeka were predominantly winter annuals with no summer annual species observed. On the other hand, Wabaunsee was predominantly summer annuals with little to no winter annual weed emergence observed. Each location will be analyzed based on weed species present, while conclusions will be based on weed species' life cycle.


 Summer annual weeds and grazing

In Wabaunsee, KS, treatments consisted of 0, 16, 37, 49, 65, and 92 days of grazing between December 5, 2021 and April 16, 2022. During the grazing season, cover crop biomass ranged from 133 to 2498 kg ha-1 and declined over time as days of grazing increased. This decline in biomass is consistent with other studies involving cover crop grazing during the fall, winter, and springtime (Anderson et al. 2022; Schomberg et al. 2014). Cover crop height and biomass recorded during the grazing season did not reduce weed control, but regrowth height and biomass (CC measured in the spring) did reduce weed control. As cover crop height and biomass in the spring increased, weed biomass also increased. Overall, reduced cover crop biomass negatively influenced summer annual weed biomass. Treatments with less CC biomass generally resulted in more weed biomass during the spring planting season. These data were collected on May 16, 2022, before cover crop termination and planting took place. Arguably, that is one of the most influential times when farmers are concerned with weed competition with the emerging crop. When grazing treatment reached around 65 days of grazing, a decline in weed control was observed before planting. As little to no research in the semi-arid Great Plains region of the United States has been conducted to discover the influence of cover crops on summer annual weed biomass, these data stand-alone (Kumar et al. 2020).

 Winter annual weeds and grazing

The two locations with winter annual weed species present were Castleton and Topeka, KS. At Castleton and Topeka, CC biomass ranged from 102 to 703 kg ha-1 and 77 to 828 kg ha-1, respectively, over the grazing season with a general decline over the grazing period, similar to biomass at Wabaunsee. During the grazing season and prior to cover crop termination at Castleton and Topeka, there was no influence of grazing cover crops on winter annual weed control. This was consistent with findings out of Missouri where, in some cases, grazing cover crops influenced chickweed and henbit control, but in other cases, it did not (Dhakal et al. 2022). Previous research and these data suggest that control may be more dependent on grazing interactions with other environmental conditions or winter annual weed densities.

 Forage Quality

Forage quality was assessed at all locations in Kansas including Castleton, Wabaunsee, Topeka, Clay Center, and Ellsworth. Previous research indicated a positive linear relationship observed between NDF and forage maturity (Nordheim-Viken, Volden 2009). The NDF value indicated the total cell wall constituents and a higher value in turn results in more energy necessary to break down the forage (Ball et al. 2001). The highest NDF values were observed with cereal rye at Ellsworth over the grazing season from November to January ranging from 44.4 to 56.3. This was consistently high compared to other values observed at Clay Center (29.3) and Topeka (33.5). These values were significantly lower compared to other on-farm research that recorded cereal rye NDF values at boot stage in Ontario, Canada (Landry et al. 2019). However, in Kansas, many farmers utilize cereal rye for cattle grazing long before boot stage and therefore take advantage of lower NDF values, which resulted in better forage for livestock.

Relative feed value is “an index for ranking cool-season grass and legume forages based on combining digestibility and intake potential. Calculated from ADF and NDF. The higher the RFV, the better the quality. It is used to compare varieties, match hay/silage inventories to animals, and to market hay” (Ball et al. 2001). As RFV increases, the economic value of the forage follows. Overall, RFV should not be used to compare different species of forages, rather to rank feeds of the same species (Dunham 1998). The lowest RFV values were observed in Ellsworth ranging from 100 to 144 while the highest values were in Clay Center ranging from 156 to 255.

Relative forage quality is also an index of forages and is determined from both dry matter intake (DMI) and TDN. Every class of livestock has different RFQ value requirements (Hancock et al. 2014). For example, young heifers and stocker cattle need around 120 to 140 RFQ values while lactating beef cattle need around 115 to 130. Relative forage quality is typically greater for younger forage. In our study, RFQ was generally higher earlier in the grazing season at all locations excluding Ellsworth. This might have stemmed from the previous crop of sorghum. The highest RFQ values were observed at Clay Center, Topeka, and Wabaunsee with values at 221 (0 days of grazing), 212 (0 days of grazing), and 234 (37 days of grazing), respectively.

Crude protein values are based on nitrogen content and can be influenced by the amount of rainfall on the forage (Ball et al. 2001). Crude protein values at all locations were variable. At Clay Center, Topeka, and Wabaunsee, the lowest values were observed at the beginning of the season and the highest values towards the end of the grazing season. The highest values were observed at Clay Center with recordings at 22.9 to 23.9. This is high for cereal rye, but values were sampled when plants were young and naturally have high CP. Other research has also found similarly high CP values in young cereal rye plants (Kantar et al. 2011).

Acid detergent fiber is used to calculate digestibility and TDN and is critical to hay value and forage quality since it “contains cellulose, lignin, and silica, but not hemicellulose” (Ball et al. 2001). As ADF increases, the value of forage decreases. ADF was variable, but highest values were observed in the central areas of the state where rainfall is lesser than in the eastern portion which had lower ADF.

At all locations grazing occurred in January 2022. The January 7, 2022 Kansas Direct Hay Market Report contains alfalfa forage quality and prices that are displayed alongside forage values from this experiment. Crude protein values of cereal rye and triticale compared to fair alfalfa crude protein values in most cases. This is the main report in Kansas that gives accurate and current hay prices based on quality. These values are presented to provide background information for what capital farmers may be gaining from grazing cover crops instead of purchasing hay.

Cereal rye and triticale cover crops at all five Kansas locations provided adequate CP, ADF, and NDF values to support feeder calves and cow/calf pairs during the fall, winter, and spring months. Cover crop biomass can affect grazing availability, but in years with adequate rainfall, cover crops can take the place of hay. Farmers should take advantage of quality cover crop forage when grazing cattle at low stocking rates at early cover crop growth stages.


Grazing cover crops in Kansas can negatively influence weed suppression depending on weed life cycle. Summer annual weed species such as Palmer amaranth and giant foxtail were more dominant in longer grazed cover crop treatments. However, these same effects were not observed with winter annual weed species, likely due to the similar life cycle of cereal rye and triticale. Farmers and ranchers should be cautious when grazing cover crops if the main use of cover crops is for suppression of aggressive summer annual weed species. If farmers plan to graze cover crops, they should look to early seeding in the fall to produce larger amounts of biomass early in the growing season which would allow for earlier grazing. Cattle, in turn, could be removed from grazing earlier in the growing season to allow cover crops to recover and compete with summer annual species in the springtime. Alternatively, a reduced stocking rate to ensure adequate ground cover and plant recovery time could be a viable option for cattle grazing in the late winter or early spring.

Cover crops provide a forage source for livestock during the winter months when pastureland is not readily available for grazing due to dormancy. Although grass-based cover crop mixtures do not contain the nutritive value that high quality alfalfa does, it is still providing adequate feed for cattle at a time when costs may be high for hay. Farmers and ranchers should utilize these data to align with their strategies for grazing, cattle production, crop management, and weed control.

Participation Summary
5 Farmers participating in research

Educational & Outreach Activities

5 Consultations
1 On-farm demonstrations
5 Webinars / talks / presentations
1 Workshop field days

Participation Summary:

100 Farmers participated
5 Ag professionals participated
Education/outreach description:

Educational activities included a poster presentation at North Central Weed Science Society, an AM radio interview, an extension field day, a SARE presentation, and there will be journal articles published in the future.

Project Outcomes

10 Farmers reporting change in knowledge, attitudes, skills and/or awareness
2 Farmers changed or adopted a practice
Project outcomes:

This project shows consequences and benefits that farmers may encounter when they choose to get forage value from sustainable cover crops. I think it offers a look at why farmers might not choose to do this, but also show them certain outcomes if they do. 

Knowledge Gained:

This project really allowed me to explore and take a deep look at practices that farmers are using to be sustainable. However, it showed me how difficult these changes can be for farmers and made me think differently about how I present them to farmers. 

Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.