How Tall Does Biomass Sorghum Grow?

Biomass sorghum refers to special cultivars of the Sorghum bicolor species that are grown specifically for bioenergy production rather than for grain or forage. These sorghum varieties have been bred to produce very high biomass yields through traits like increased height, thicker stems, and high sugar content in the stalks.

Sorghum is an ancient crop that originated in Africa, where it has been cultivated for over 4,000 years as a cereal grain and animal fodder. Beginning in the late 1800s, sorghum was introduced to the United States and became an important crop in the south and midwest for grain, forage, and syrup production (Genera Inc, 2017). Over the last couple decades, specialized high-biomass sorghum hybrids have been developed through plant breeding efforts to optimize the crop specifically for bioenergy feedstock production.

Typical Height of Grain and Forage Sorghum

Grain and forage sorghum varieties typically range in height from 3-4 feet up to 10 feet or more, depending on the variety and growth conditions. According to an article on Crop Science from Bayer, a sorghum plant with zero dwarfing genes could potentially reach heights of 9-12 feet or more (source). However, most commercial grain sorghum hybrids contain dwarfing genes that limit their height.

Forage sorghums are bred specifically for biomass production and can grow even taller. An article from DeerAssociation.com states that some forage sorghum varieties can reach 10 feet tall (source). The height is influenced by genetic factors like the number of dwarfing genes, as well as environmental conditions like soil fertility, moisture, and plant density. Denser plantings typically result in taller, spindly plants as they compete for sunlight. Overall, typical sorghum heights under normal field conditions range from about 6-10 feet for most grain and forage types.

Development of Tall Biomass Sorghum

Breeding efforts to develop taller biomass sorghum hybrids began in the late 2000s as researchers sought to increase biomass yields. Key programs driving these efforts included the USDA-ARS in College Station, Texas and the University of Nebraska’s sorghum improvement program.

One influential figure was Bill Rooney at Texas A&M University, who helped lead research into breeding taller sorghum hybrids with high biomass yields. In 2009, Rooney’s team released early tall hybrids like ES5200 which could reach over 4 meters in height (https://generainc.com/wp-content/uploads/2020/01/Biomass-Sorghum-Production-Guide.pdf).

Stephen Kresovich at the University of Nebraska also contributed significantly through his work breeding high biomass sorghum varieties. His program developed taller hybrids like Sugar Drip that exhibited excellent height and tonnage.

Through the efforts of these and other scientists, sorghum hybrids were developed that exceeded 4 meters in height, far surpassing the stature of traditional grain and forage types.

Average Height of Current Biomass Sorghum Hybrids

Biomass sorghum is a fast growing crop that was developed to produce high biomass yields. Typical commercial biomass sorghum hybrids today grow to heights of around 400-500cm (13-16ft) on average, though heights up to 610cm (20ft) are not uncommon under optimal growing conditions. This makes biomass sorghum significantly taller than traditional grain and forage sorghum varieties.

According to research conducted in Hawaii comparing commercial biomass sorghum hybrids to grain and forage types, biomass sorghum reached maximum plant heights of 338cm and 319cm, compared to heights of only 254cm for forage sorghum and 63cm for grain sorghum [1]. Other reports confirm average heights for biomass sorghum ranging from 350-500cm, while grain sorghum averages only 100-170cm in height [2].

This dramatic increase in stature for biomass sorghum makes it well-suited to producing the high yields of lignocellulosic biomass needed for applications like bioenergy production. At the same time, biomass sorghum’s tall heights necessitate specialized equipment for optimal planting, management and harvesting.

Record Heights for Biomass Sorghum

There have been reports of exceptionally tall biomass sorghum hybrids reaching heights over 20 feet. In trials by Ceres Inc., some of their hybrids reached up to 22-24 feet tall under ideal conditions (https://biofuels.ifas.ufl.edu/biomass-sorghum.shtml). Other industry sources have claimed hybrid heights exceeding 30 feet, although this is likely under absolute optimal conditions.

While these record heights demonstrate the incredible genetic potential for height in biomass sorghum, the ideal height for maximum biomass yield is typically much shorter. Most commercial hybrids today range from 10-16 feet tall at maturity. According to Texas A&M research, the optimal height for balancing biomass production and standability ranges from 12-15 feet (https://www.ars.usda.gov/ARSUserFiles/3025/Performance_%20evaluation_of_biomass.pdf). Excessive height can lead to lodging issues that reduce yield and increase harvest costs.

So in summary, while exceptionally tall sorghum has been developed, the ideal balance for agronomic performance is around 12-15 feet tall. Breeding efforts continue to maximize height within this optimal range to increase overall biomass productivity.

Factors Influencing Biomass Sorghum Height

Biomass sorghum height is influenced by several key factors including genetics, environment, and management practices. Genetics play a major role, as breeders have specifically selected tall hybrids that can reach over 4 meters in height. According to research, sorghum biomass yields are positively correlated with plant height, so breeders select for tall genotypes (Habyarimana et al., 2020).

The location and environment where biomass sorghum is grown also impacts height. In ideal growing conditions with warmer temperatures, adequate moisture and nutrients, sorghum can reach its maximum genetic height potential. Field trials show that biomass sorghum grown in tropical environments like Hawaii can exceed 4 meters, while the same hybrids grown in more temperate environments may only reach 2-3 meters (Meki et al., 2017).

Management practices such as planting date, row spacing, and fertilizer rates can also influence sorghum height. Earlier planting when soils are warmer allows a longer growing season for taller growth. Wider row spacing reduces competition and increases light interception. Adequate fertilization, especially nitrogen, provides nutrients needed for vigorous growth. Growers can optimize these practices to maximize height potential for their environment and hybrid (Sadia et al., 2018).

Optimizing Biomass Sorghum Height

When growing biomass sorghum, it’s important to optimize plant height for maximum yield while maintaining standability. Excessively tall hybrids can become top-heavy and prone to lodging or stalk breakage before harvest.

The ideal height depends on the specific hybrid and local growing conditions. Breeders aim to develop stiff-stalked hybrids that can achieve over 4 meters (12 feet) under ideal conditions, while still standing up until harvest.

In areas prone to strong winds or heavy rain, shorter hybrids around 3-4 meters (10-12 feet) may be selected to reduce lodging risks. The density and spacing of the crop can also impact height, with wider rows allowing plants to grow taller without as much mutual shading.

Growers should research height ratings for specific hybrids and plant taller varieties on only their most productive land. Field trials help determine optimal plant populations for achieving maximum height without excessive lodging in local conditions.

With proper hybrid selection and agronomic practices, biomass sorghum can reliably reach heights over 3 meters (10 feet), generating high biomass yields for bioenergy production.

Height Measurement Methods

Properly measuring the height of biomass sorghum requires using consistent techniques across the field to get accurate results. There are a few key factors to consider when measuring sorghum height:

Measure from the ground level to the top of the panicle, or the base of the unfurled flag leaf if panicles have not emerged yet. Ground level should be measured right at the plant base, excluding any raised soil around the stem. Be consistent in measuring from soil surface versus raised root crown.1

Take measurements from at least 5 representative plants within a plot and average the values. Avoid sampling only the tallest or shortest plants, which can skew results.

Take height measurements at the same growth stage across all plots, such as at flowering stage. Comparisons are more accurate when plants are at a similar developmental stage.

Measure at the same time of day to minimize differences due to diurnal plant movement. Morning measurements are recommended.

Use a fixed ruler, yardstick, or meter stick rather than subjective visual height estimates. Stand perpendicular to the plant when taking measurements.

Record any lodging or differences in stand density, as sparse stands with few plants per area may appear taller. Account for leaning stems versus perfectly vertical posture.

Consider measuring from aerial imagery using drones or phenotyping platforms to sample heights more quickly across large trials.2

Advantages of Tall Sorghum Stature

One of the key advantages of taller stature in biomass sorghum is the strong positive correlation between plant height and biomass yield. According to Genera Energy, field research has demonstrated that “the yield benefits are quite obvious when standing next to a field of 16 foot tall biomass sorghum.” Studies have shown biomass yields exceeding 30 dry tons per acre from the tallest hybrids, compared to 20 tons per acre or less from shorter grain and forage types (Genera Energy).

The taller and bulkier stature of biomass sorghum also provides advantages for harvesting and transportation. The high yields obtained from tall hybrids mean more biomass material can be harvested from each acre, improving per acre profitability. The dense growth allows efficient harvesting with commercial forage equipment. When baling biomass sorghum, the taller stalks form larger, heavier bales that maximize each loading for transport to the biorefinery (UF IFAS). Thus, the tall stature of biomass sorghum directly contributes to higher biomass yields and more efficient collection and transport.

Conclusions

In summary, biomass sorghum is a tall, fast-growing crop that can reach heights ranging from 4-5 meters on average to as tall as 9 meters under ideal conditions. The original grain and forage sorghum crops grew to modest heights, but focused breeding has created today’s extra-tall hybrids specifically for biomass production. While maximum possible height depends on factors like genetics, soil quality, and climate, target height is based on balancing higher yield with ability to withstand lodging or stalk breakage. Careful field management can optimize sorghum height by addressing nutrients, planting density, harvest timing, and environmental stresses. With its towering stature and rapid growth, high-biomass sorghum offers advantages for bioenergy, forage, and industrial uses.

In conclusion, modern biomass sorghum reaches impressive heights, typically averaging 4-5 meters but capable of growing as tall as 9 meters. By leveraging the latest hybrids, growers can optimize height for their conditions to maximize yield. With its unmatched scale and productivity, super-tall sorghum unlocks new value across a range of commercial applications.