Evaluating Rotations of Cover Crops and Summer Annual Forages for Yield, Nutritional Value, Effect on Soil Nutrient Profile, and Economic Sustainability as Forage for Beef Cattle
In addition to protecting Iowa’s water quality and preserving valuable topsoil and nutrients, cover crops can provide an additional forage source to Iowa beef producers. While the long-term benefits of cover crops such as reducing soil erosion and improving soil organic matter are well documented, it can be difficult to put a dollar value on those returns on investment. Producers may be more inclined to use cover crops if they can realize a short-term benefit in addition to the long-term conservation benefits. One logical potential short-term benefit that could incentivize this practice is the utilization of cover crops as a forage resource to stretch the feed supply, extend grazing and increase carrying capacity. However, a more complete understanding is needed for utilization of alternative forages by beef cattle across the state.
Since 2012, Iowa has lost another 125,000 acres of permanent pasture while beef cow numbers have rebounded to just over 938,000 head, according to the 2017 Census of Agriculture. This data shows a continuing trend of beef cattle producers maintaining or increasing production on fewer and fewer acres of permanent pasture. If Iowa producers can use cover crop forages as beef cattle feed resources, cover crops will be more attractive as a practice with multiple benefits.
The objective of this study is to evaluate potential yield, nutritional value, effect on soil nutrient profile and economic sustainability of cover crops used in rotation with various summer annual forage species. This project will demonstrate and aid in development of best management practices of rotating winter cover crops and summer annuals to optimize forage production while improving soil and water quality.
To achieve these objectives, this study will:
- Evaluate nutrient content and potential yield of various cover crops and summer annuals used in rotation as conservation practices and forage resources for beef cattle. Forage samples will be taken to determine forage yield and nutritional value of the cover crops and the annual species.
- Determine soil nutrient loss when cover crops and annuals are mechanically harvested. Soil samples will be taken at the beginning of the study to establish a baseline for soil phosphorus, potassium, pH and organic matter. Nutrient content of forage samples will be used to calculate estimated nutrient removal with forage harvest.
- Demonstrate integration of winter cover crops in rotation with summer annuals to optimize forage production for beef cattle.
- Educate producers through extension and outreach efforts, sharing findings through a variety of formats and events.
Note: Project reports published on the INRC website are often revised from researchers' original reports to increase consistency.
Key Research Questions
- What are reasonable expectations for nutrient content and yield of various cover crops and summer annuals used in rotation as farm conservation practices and forage resources for beef cattle?
- What is the expected crop nutrient removal when winter cover crops and summer annuals are mechanically harvested?
- Additional objectives included demonstration of winter cover crops in rotation with summer annuals to optimize forage production for beef cattle and education of producers through extension and outreach efforts.
This forage plot trial was designed to evaluate potential yield, nutritional value and forage crop nutrient removal of winter annual forage species used in rotation with various summer annual forage species. The study began in the summer of 2019 with the seeding of five species of summer annual forages: pearl millet, Japanese millet, sorghum sudangrass, crabgrass and teff. Following sampling, harvest and termination of the warm season species, cool season species were no-till drilled in the fall to be sampled and harvested the following spring. Barley, cereal rye, triticale, hard red winter wheat and forage winter wheat were chosen for the cool season species.
Eight replicates of each species were seeded at three of the outlying ISU Research Farms (Armstrong, Neely-Kinyon and McNay) with half of the plots (four) receiving no Nitrogen (N) fertilization and half receiving 50 lb of N/acre. The trial was repeated a second year with summer annuals being planted, sampled and harvested during the summer of 2020 and the winter annuals being planted in the fall of 2020 and sampled and harvested in the spring of 2021. Warm season forage yield data are reported in Figure 1. (Find associated Tables and Figures referenced at: INRC_Final_Report_2019-08_CClarketal_figures_and_tables_only.pdf). The warm season species produced approximately 1 -2 tons of dry matter per acre with considerable variation among species and across farms. Sorghum sudangrass and pearl millet showed the greatest yields while Japanese millet, teff and crabgrass were inconsistent across farms and years.
The warm season species in this study showed a relatively inconsistent response to fertilization with N. Over all sites and all years, only sorghum sudangrass and pearl millet showed a statistically significant response to treatment with 50 pounds N/acre, with approximately a 40% increase in yield.
In 2019, the warm season forages were harvested once in August. However, in 2020, forages were sampled based on maturity in August (targeting soft dough stage) and a second cutting of each species was sampled in September. Harvest cutting height likely impaired regrowth for these warm season forages. Recommended cutting height would be approximately 8 inches (or 2 nodes on sorghum sudangrass) to allow for optimal regrowth; however, first cutting harvest left approximately 4 inches of residual height due to forage harvest equipment limitations at the farms. In general, second cutting forage yields were modest at best for all species due to cutting height and shortened window between cuttings. For some of the warm season species, second cutting yield may have been improved by allowing more time between first and second cuttings. However, second cutting harvest was greatly influenced by the planned planting date for the following cool season species. Interestingly, the Japanese millet showed essentially no regrowth and headed out at just a few inches tall. It is also important to note that 2020 was a dry summer, and Japanese millet tends to require more moisture than the other warm season annual species. For statistical analysis of 2020 data, first and second cutting yields were added together to measure total season-long forage yield. Figure 2, however, shows total yield and yield by cutting.
Of the five warm season forages used, teff and crabgrass proved to be the most difficult to establish, with minimal or essentially no yields in some of the plots across locations. For example, there was no significant growth, and virtually zero yield for crabgrass in 2019 for both McNay and Neely-Kinyon nor for teff in 2019 at Neely-Kinyon. For both species, minimal early growth allowed weed pressure that competed with the forage and further inhibited growth. At McNay, teff and crabgrass took off later in the season but struggled early in the growing season. Teff is expected to germinate in 3-5 days, so its slow start may have had more to do with seedbed preparation and seeding depth. Crabgrass can take several weeks to germinate, which may explain its slow start in this study. Although often thought of as more of a weed, crabgrass can produce high-quality, palatable forage. Crabgrass is also a persistent and drought-tolerant species which was why it was chosen for this study to demonstrate its use as an option for producers. Although crabgrass was difficult to establish, it proved to be very persistent, with volunteer growth showing up in subsequent seasons in crabgrass plots and in adjacent plots. Its competition with other forages may be a challenge as the project moves forward. Its slow start negatively affected yield but nutritional value was comparable to that of other warm season forages in this study. Therefore, despite modest yield, its persistence, drought tolerance and forage quality may make crabgrass a viable forage option in some situations.
Warm season forage quality is reported in Table 1, and mineral profiles are reported in table 2. At the time of sampling, most species were in the late vegetative stages to early reproductive stages of growth to mimic grazing or harvest for silage. The idea was to optimize yield and quality and to mimic real-world utilization by grazing or harvest for silage. In general, the warm season forages contained adequate energy and protein levels to support late-lactation or early-to-mid-gestation requirements of a beef cow. Timing of warm season harvest and warm season forage quality align relatively well with the nutritional requirements for spring-calving herds in Iowa. However, especially with the warm seasons, some individual forage samples fell short of meeting cow requirements, so it is important for cattlemen to be mindful of forage quality, particularly when these annual forages are the only source of nutrients.
As expected, there was some variation in forage quality year-to-year and farm-to-farm. Some of that variation was likely due to weather while some can likely be attributed to other site differences and differences in maturity at harvest. For example, crabgrass and teff were difficult to establish and grew slowly early in the growing season. Therefore, these forages were shorter and less mature when sampled for nutritional value, driving the greater forage quality results for these species. For other species, some plants had headed out and were more mature than ideal at the time of sampling, affecting their forage quality results.
One of the greatest opportunities of summer annual utilization is forage availability at a time when Iowa cool season pastures are dormant. At the time of typical warm season harvest in August and September, cool season pastures are often sparse in quantity and lacking sufficient quality to meet the needs of late-lactation. Utilization of warm season annuals during this time can provide better nutrition and allow time for perennial pastures to rest and recover.
Nutrient removal values of phosphorous (P2O5) and potassium (K2O) by warm season species are reported in Table 3. Nutrient removal for each species was calculated based on nutrient content of forages as reported in forage quality data. Nutrient removal values were comparable to values in “A General Guide for Crop Nutrient and Limestone Recommendations in Iowa (PM1688)” for forage species already included in the publication. Nutrient removal data can help farmers determine what nutrient(s) to put back on fields after mechanical harvest of these forages.
Cool season forage yields are described in Figure 3. The cool season species produced approximately 0.5 to 1.5 tons of dry matter per acre and showed a relatively consistent response to N application. Treatment of the cool season plots with 50 pounds N per acre resulted in approximately a 50% increase in yield compared to those plots without N fertilization. While we see greater yield due to N fertilization, it is important to carefully analyze the economics of fertilization, considering fertilizer prices. At the McNay site, to optimize forage yield and quality for each species, cool season species were sampled based on forage maturity, targeting sampling at approximately boot stage for each species.
Table 4 describes harvest dates for the various forages at McNay, and Figure 4 shows the average cool season forage yield data at McNay for 2020 and 2021. Triticale and the wheat species reached maturity approximately 7-14 days after barley and cereal rye. The later sampling dates for the triticale and wheat species likely contributed to greater yields for these species compared to cereal rye (Figures 3 and 4). Knowledge of these growth patterns can help producers select the appropriate species to reach their farm’s goals. If following the cool season forages with a warm season cash crop, planting date of the cash crop may be a primary concern, so an earlier maturing species such as cereal rye would be a good choice. Alternatively, if the priority is forage production, later maturing species like triticale or wheat species may offer greater yields. Cool season forage quality is reported in Table 5 and mineral profiles are reported in Table 6. Much like the warm season forages, at the time of sampling, most species were in the late vegetative stages to early reproductive stages of growth.
In general, assuming intake is not limited, the small grain forages contained adequate energy and protein levels to support late gestation and early lactation requirements of a beef cow. Again, some individual forages samples fell short of these requirements, so it is important for cattlemen to be mindful of forage quality. The timing of spring forage availability aligns well with calving season for many Iowa spring-calving herds. Cool season forage stands can serve as calving pastures and provide high quality forage for spring-calving cows. Generally speaking, the nutritional value of the cool season forage species harvested in the spring are relatively consistent with the expected nutritional value of perennial pasture at that time of year. Like the warm season forages, variation in forage quality was driven by weather, plot site differences and differences in maturity at harvest. Barley, for instance, grew slowly early in the growing season and was, therefore, shorter and less mature when sampled for nutritional analysis, likely driving the greater forage quality results described in Table 6. Alternatively, some of these forages decrease in digestibility and overall quality quickly after maturation. Some plants had headed out and were more mature than ideal at the time of sampling, affecting the forage quality results for these species Barley is often noted for being a higher quality and highly palatable forage and investigators had received questions about whether it would overwinter in Iowa. In this study, barley did not overwinter well, showing very modest yields at McNay (the southernmost farm) and essentially no growth at the Armstrong and Neely-Kinyon sites. Therefore, barley does not seem to be a good choice for a fall-seeded cool season crop in Iowa. Although barley may not be the best choice to plant in the fall, a recent ISU Extension project in east-central Iowa shows more comparable yield to other spring-seeded annual forage species when planted in the spring. It is worth noting that while there were no significant differences between the HR winter wheat and the forage wheat in terms of yield or forage quality, there was a noticeable difference in leaf texture with the forage wheat having softer leaves. Although no grazing was done in this study, other research has noted greater palatability of the forage wheat when grazed by cattle.
Nutrient removal values of phosphorous (P2O5) and potassium (K2O) by cool season species are reported in Table 7. Nutrient removal for each species was calculated based on nutrient content of forages as reported in forage quality data. Nutrient removal values were comparable to values in PM 1688, “A General Guide for Crop Nutrient and Limestone Recommendations in Iowa” for forage species already included in the publication. Nutrient removal data can help farmers determine what nutrient(s) to put back on fields after mechanical harvest of these forages. Major costs of production include seed cost, fertilizer, and the equipment and labor associated with seeding and harvest. Costs will obviously vary year to year but yield and forage quality data from this study should help producers weigh those costs versus potential feed production and value. For the cool season forage species in this study and two of the warm season species, there was a significant response to N treatment. However, in times of high fertilizer prices, producers must weigh carefully the cost of N versus the potential increase in yield. Additional costs may include the replacement of removed P2O5 and K2O when forages are mechanically harvested and herbicide applications depending on weed pressure and field management.
Team members participated in approximately 15 total field days, meetings and/or live presentations with information about this study. Additionally, six virtual presentations were done as webinars with some recorded and made available for on-demand viewing. Two examples of virtual presentations are available at the following links.
- Erika Lundy Woolfolk – Iowa Learning Farms Webinar August 2020 , at: https://vimeo.com/452317016
- Research team – Virtual Annual Forage Field Day – June 3, 2021. The presentation was recorded and is available online via the Iowa Beef Center website and/or Youtube channel, at: https://www.youtube.com/watch?v=cxFzVEBNnSA
Information from the study has been included in popular farm press articles and Iowa State University Extension and Outreach Research Farm progress reports.
- McNay Farm Progress Report Year 1: https://www.iastatedigitalpress.com/farmreports/article/id/11492/
- MacNay Farm Progress Report Year 2: https://www.iastatedigitalpress.com/farmreports/article/id/12996/
The project is ongoing for two more years with funding from the Southern Iowa Forage and Livestock Committee. To evaluate additional species, some changes have been made to the species planted to include a hybrid rye variety, German millet and sudangrass. With the continuation of the study, the plots will be discussed at ISU research farm field days for the next couple of years. Investigators also plan to create an Iowa State University Extension and Outreach publication summarizing the study and its findings.