Warm-Season Grass Binary Mixtures for Biomass in the Northeast

J.H. Cherney1, D.J.R. Cherney2, and M. Davis3
1Section of Soil & Crop Sciences, 2Dept. of Animal Science, Cornell University, and 3Farm Manager, Cornell Willsboro Research Farm, Willsboro, NY

Over five million acres of marginal agricultural land in the Northeast USA are no longer in use and have great opportunities for grass biomass production, although environmental or other supplemental compensation may be required for profitable production on low-yielding marginal land. Warm season grasses are considered a viable herbaceous second generation biofuel feedstock but are better suited to marginally productive cropland Future selection through breeding should have a significant focus on low-input types of environments.

Additional environmental benefits may accrue when mixtures are used instead of monocultures. Studies have suggested that polycultures sequester more carbon in the soil profile and have less N leaching compared to monocultures. Profitability in biomass production, however, is most strongly influenced by yield, and we focused on yield potential in this study.

Experimental layout

A long-term plot study was sown in 2010 in Ithaca (central NY, Williamson fine sandy loam soil) and Chazy (northern NY, Roundabout silt loam soil), and was completed in 2018. A goal was to determine if binary mixtures of warm-season grasses would result in increased yield over pure stands.

Three replicates of 12 treatments compared pure species with binary mixtures (Fig. 1). Binary mixtures had one species seeded in one direction, and the second species seeded perpendicular to the first. Pure species also were seeded twice, with one half the total seed sown perpendicular to the other half. Pure switchgrass and Atlantic coastal panic grass plots were seeded at 10 lbs pure live seed (PLS)/acre. Pure big bluestem plots were seeded at 12 lbs PLS/acre. Mixtures contained half the seeding rate of pure species plots for each species in a binary mixture. All entries were commercially available varieties, with the exception of RC Big Rock switchgrass, which was an experimental selection from Cave-In-Rock (REAP-Canada, Ste-Anne-de-Bellevue, QC). Insufficient seed was available of Timber switchgrass to seed at both sites.

Fig. 1. Plot layout at the two NY sites.

Plots (15’ x 15’) were fertilized with 50 lbs N fertilizer/acre at spring green up each year. Roundup was sprayed in the spring prior to warm season grass green up to control weeds after 2013. A few weeds were resistant to Roundup and remained, such as milkweed. Plots were well established by the 2013 growing season. Plots were harvested for yield determination each year in early October generally after first frost at a 4” stubble height using a flail harvester, harvesting 78 sq. ft. of plot area (3’ x 13’ twice per plot). Samples were collected for dry matter (DM) determination.


The more southern, generally wetter, Ithaca site averaged 22% greater yield across all years and species combinations. Ithaca long-term average precipitation is 4.5” per year more than Chazy (Plattsburgh, NY weather station), and Ithaca averaged 5.5” more per year during the experiment. Although Chazy is considerably farther north than Ithaca, long-term average heat units are very similar. Over the 2013-2017 period from May 1 to Oct. 1, both sites averaged 4916 GDD per growing season (base 32F). Warm season grass mixtures behaved differently on different sites. At Chazy, big bluestem (BB) tended to compete very well in mixtures with switchgrass (SW), while at the Ithaca site switchgrass tended to be the major component.

Big bluestem was the slowest species to become fully established, but Prairie View BB pure stands were the highest yielding at the Chazy site, averaged over five years. RC Big Rock switchgrass selection had the greatest yield in Ithaca for pure SW stands, averaging 6.6 tons DM/acre over 5 years. Cave-in-Rock SW (CAV) and the CAV-Prairie View BB mixture both yielded 13% less at Chazy than Ithaca, but pure Prairie View stands produced similar yields at both sites. Upland switchgrass mixed with Prairie View BB tended to produce the best overall results and was the most compatible mixture (Fig. 2). Other mixtures tended to become mostly monocultures over time.

Fig. 2. Average yields of pure switchgrasses (SW) vs. SW mixtures with big bluestem (BB).

Atlantic coastal panic grass (ACP) was promising the first year, but quickly deteriorated to a weak stand after the first year, and had significant weed invasion in later years, particularly at Chazy. BoMaster switchgrass struggled in pure stands and became a very minor component of mixtures. In later years, big bluestem and switchgrass tended to invade plots with weaker stands, as ripe seed was scattered each year during harvest with a flail harvester.


At both sites, mixtures of Cave-in-Rock SW and ACP quickly became pure switchgrass stands. By the end of the trial, mixtures of Cave-in-Rock and Suther BB were pure switchgrass at Ithaca, and averaged 10% BB at Chazy. BoMaster SW and ACP, as well as mixtures of these two, tended to be weak stands at both sites, with up to 25% weeds observed in the summer of 2018. Prairie View BB and BoMaster SW mixtures were essentially pure big bluestem stands in 2018 at both sites. Suther BB and Cave-in-Rock SW mixtures were pure switchgrass in Ithaca, and averaged 10% big bluestem in Chazy. Prairie View BB and Cave-in-Rock SW mixtures averaged 15% bluestem in Ithaca and 35% bluestem in Chazy, at the end of the trial.

Ground cover

Plots in Ithaca were observed for ground cover in the spring of 2018 (Fig. 3). The three replicates were very consistent in ground cover. Switchgrass provided the most ground cover early in the season, with RC Big Rock SW appearing to have the greatest ground cover. BoMaster was the weakest switchgrass, typically with weed infestations. Approximately 50% of the ground area was bare in BB plots, but open areas were generally free of weeds. Even less surface area was covered by ACP, and open areas tended to be infested with weeds annually. With the exception of ACP at both sites, and BoMaster SW at Chazy, other species and species combinations developed into a closed canopy by mid to late summer, regardless of the ground cover observed in spring.


The only mixtures with a significant contribution from both species were Prairie View BB and Cave-in-Rock SW mixtures. These mixtures had considerably more switchgrass at the Ithaca site compared to the Chazy site. Our results agree with other studies suggesting that species mixtures will be largely influenced by environmental variation. Results from a single location may not be applicable to other environments. Mixtures can improve yields mainly in the establishing years, with the potential for better yield stability over the life of the stands. Farmers should consider planting adapted cultivar mixtures of big bluestem and upland switchgrass for enhanced yield and yield stability. Improving seedling establishment of big bluestem should be an important breeding priority for more widespread adoption of this crop.


This work was supported by the USDA National Institute of Food and Agriculture, Multistate project 218756. Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the authors and do not necessarily reflect the view of the National Institute of Food and Agriculture (NIFA) or the United States Department of Agriculture (USDA).

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What’s Cropping Up? Volume 28, Number 4 – September/October 2018

Harvest Strategies and Forage Quality Monitoring for Corn Silage

Joe Lawrence, Cornell CALS PRO-DAIRY; Margaret Quaassdorff, NWNY Cornell Cooperative Extension

A great deal of time is spent on the basics of an optimum corn silage harvest. This time is justified as these steps are critical to a successful harvest, where the decisions made during a very short time period impact the farm’s production performance and economics for the upcoming year. These important decisions include harvesting at the proper dry matter, adequate kernel processing, proper length of cut, and proper packing and covering of bunk silos. An overview of this information is covered in Setting the Stage for Success: Corn Silage Harvest. The following will cover additional considerations for understanding and managing the forage quality of the crop.

As part of the Corn Silage Hybrid Evaluation program, we have focused significant attention over the last two growing seasons on the interactions between growing environment and corn silage forage quality. While this work is still developing, it does build on earlier knowledge of the impact of growing conditions on plant development, and provides some insight into managing the corn silage crop for forage quality.

Plant Development, Weather and Fiber Digestibility
Plant physiologists have long understood that characteristics of corn ear development are determined early in the growing season. Before the crop even reaches the reproductive stage of growth it has already determined the number of kernel rows per ear and the number of kernels per row. It is also understood that hot weather around the time of silking (three to five weeks) can lead to increased lignin content in the plant.

In recent years, long term fiber digestibility measurements by laboratories have become more common. Neutral Detergent Fiber (NDF) digestibility at 30, 120 and 240 hours is now commonly measured, as well as the undigested NDF (uNDF) at these same time points. In 2015 and 2016, the Dairy One Forage Lab conducted a study where they tracked season-long weather information and measured its impact of uNDF content of the silage.

Some notable results included;

  • Decreases in fiber digestibility (increases in uNDF) as both precipitation and heat accumulation increased throughout a growing season, with the most significant impacts in lowering fiber digestibility found during the months of:
    • August for rainfall (particularly at 240 hours)
    • June for Growing Degree Day (GDD) accumulation (particularly at 30 hours)

While we have seen these same trends in the Corn Silage Hybrid Evaluation program, we are awaiting more site years of data in order to draw stronger conclusions. The impact of this information on the 2018 crop will be of interest as we have had an overall warmer than average growing season, despite a relatively cool June, in addition to above average rainfall in August after excessively dry to drought conditions earlier in the season.

Taking Forage Samples at Harvest to Map Forage Quality

Given the number of factors that affect forage quality, and their field specific nature, we continue to encourage producers to take samples at harvest, making sure to record both hybrid and field location. This information will help determine the farm specific impact of growing conditions, planting dates, hybrid selection, and soil type on resulting overall forage quality and, specifically, fiber digestibility. Sampling could also be done at feedout in situations where you are able to document exactly where specific fields and hybrids are located within the storage structure.

Corn Silage Chopping Height Considerations

Corn silage harvest height tends to be a topic of discussion in years of above average yields or significant carryover from the previous year. As we enter the 2018 harvest season, many farms have adequate carryover of (generally lower digestibility) corn silage. 2018 crop conditions vary greatly, and while some areas may be faced with below average corn silage yields, there are areas of the state where yields are expected to be above average. For some, the prospect of having a corn crop with better fiber digestibility to dilute out the remaining inventory of poorer 2017 corn silage is of interest.

A number of studies have been conducted to determine the pros and cons of varying the cutting height of corn silage and Penn State provides a good review these. Given the significant impact that growing season and other management factors can have on forage quality, it is not surprising to see some variation in the end results. This is also true of the magnitude of impact that cutting height can have on corn silage. However, when averaged together, we can develop a few “rules of thumb”. In general, when starting with a cutting height of six to eight inches, raising the height of cut by approximately 12 inches, to 18-20 total inches, will result in the loss of approximately two tons per acre of yield (at 35% dry matter), but will gain five to six percentage points of NDF digestibility. Furthermore, given the fact that you will be harvesting less stalk but the same number of kernels, the percentage of starch in the resulting silage will increase.

In addition to the factors already discussed, the apparent interaction between Fiber Digestibility and Soil Type is another piece of relevant information from the Dairy One study and the Corn Silage Hybrid Evaluation program. Preliminary data indicate a trend of lower fiber digestibility on heavier soils. The work by Dairy One found that Hydrologic Class A (well-drained soils) were lower in undigested NDF (uNDF) than other soil classes.

Pre-Harvest Height Sampling

While it may be a little late for this year, those serious about making decisions to optimize yield and quality in the future may be interested in an idea suggested by Dr. John Goeser at Rock River Laboratories.

Many farms now “stage” corn fields prior to harvest to determine harvest order based on whole plant dry matter. During this time, it is suggested that you cut some stalks (Dr. Goeser recommends three to four stalks per height) from each field at different heights, chop them up, and send them to the lab for analysis that includes NDF digestibility; similar to collecting a representative bundle of stalks for whole plant dry matter testing. In this way, you will be able to better understand the impact of cutting height given the unique conditions that your corn crop experienced during the growing season, and therefore, better understand the tradeoffs between yield and quality for that season. Common cutting heights are in the range of six, 12, and 18 inches, but could vary by farm. If you traditionally chop low to the ground, then picking an increased height that provides a reasonable tradeoff based on what we know about yield decline with increased cutting height, will give you an idea of what could be gained in forage quality on your farm.

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