Agronomy

Description

Sorghum variety development has contributed to several different types being available to growers: grain sorghum, sweet sorghum, forage sorghum and biomass sorghum. Bred starting from forage sorghum varieties, biomass sorghum may be used for bioenergy purposes. Also known as high-biomass sorghum, biomass sorghum variety development has prioritized cellulosic biomass yield, not sugar levels or grain production.

The U.S. Environmental Protection Agency defines biomass sorghum as Sorghum bicolor varieties that contain at least 75 percent cellulosic content. If a Sorghum bicolor and sudangrass cross contains at least 75 percent cellulosic content, then EPA also considers the cross to be biomass sorghum.

Biomass sorghum production requires agronomic methods similar to those used when growing forage or grain crops. The crop has high yields, tall height, wide stems and a long growing season. It uses water and inputs efficiently and can generate good yields within a 90- to 100-day period. Biomass sorghum may grow to a 12- to 20-foot height. Unlike other sorghums, biomass sorghum tends to have lower soluble sugar content. Some varieties may also register moisture levels that are 10 percentage points to 15 percentage points lower than forage sorghum at harvest. Lower moisture content causes biomass sorghum to have greater energy density. By 2022, biomass sorghum yields will average an estimated 13 dry tons per acre in southern U.S. growing areas, according to Environmental Protection Agency analysis. Compared with switchgrass, biomass sorghum could achieve a given production level and use half the land required for switchgrass to record the same production output if growing conditions allow.

Site Selection

Currently, biomass sorghum isn’t commercially produced in the U.S. for biofuel use. Its production has been limited to test plots for research. Biomass sorghum has potential throughout the Corn Belt and into the southern U.S., however. The crop can grow well in the South and north to the 40 degree latitude. States that may evolve into biomass sorghum production areas are Texas, Oklahoma, Kansas, Missouri and Arkansas.

Because biomass sorghum efficiently uses water and other resources, it may grow well on marginal land that’s not well-suited for other crops. However, yields would improve if biomass sorghum were grown on fields with greater productivity. The best soils for biomass sorghum are well-drained and deep, which provides the space necessary for the crop’s large root system. However, biomass sorghum may also grow in clay and sandy soils. Areas that receive at least 30 inches of rain each year are best for biomass sorghum production; however, the crop has drought tolerance. During drought-like conditions, biomass sorghum can enter dormancy and recover when moisture becomes available. Long-term drought may influence yields, though.

Unlike perennial energy crops that require a multiyear commitment, biomass sorghum has an advantage because it requires only a one-season obligation. Thus, biomass sorghum is an option in an annual crop rotation. Rotating biomass sorghum with other crops will help to reduce disease and pest pressure. It will also prevent any one crop from depleting soil nutrients that it needs in greatest concentrations. Possible crops that may rotate with biomass sorghum include corn, soybeans and cotton.

Planting

When choosing biomass sorghum varieties, producers have several elements to consider. Some varieties may be developed for one harvest per year. Other varieties – such as sorghum and sudangrass crosses – have characteristics, such as finer stems, that make them better suited for ratooning and multiple harvests in a single season. Other factors to consider include disease susceptibility, temperature tolerance, response to other environmental conditions, maturity, drying ease, biomass composition and biomass quality.

Some biomass sorghum cultivars have a photoperiod-sensitivity characteristic. In other words, they reproduce when daylight length meets a certain number of hours. As a result, these biomass sorghum varieties shouldn’t be planted until after the given photoperiod. Photoperiod-sensitive varieties usually produce grain until late fall, or in some climates, the biomass sorghum may not reach full maturity. The photoperiod-sensitive feature and postponed or forgone reproduction results in an extended growing season and makes the crop more resilient during drought-like conditions. Other varieties mature based on thermal time, which is affected by average day and night temperatures, or alternatively, both thermal time and photoperiod may influence biomass sorghum maturity in other varieties.

Relative to grain sorghum, biomass sorghum can produce three times as much leaf and stem material. Because the cultivars don’t focus energy on reproduction, they divert more resources to generate biomass. Biomass sorghum that flowers and produces grain before harvest may have lower biomass moisture levels at harvest, but it also may have a varied biomass composition.

Within the U.S., high-biomass sorghum seed has been available from Ceres, which uses the Blade Energy Crop name for its biomass sorghum varieties. NexSteppe is another firm that has developed high-biomass sorghum varieties. It uses the Palo Alto brand for marketing its biomass sorghum varieties).

When planting biomass sorghum, soil temperatures should at least range from 60°F to 65°F to encourage germination. Ideally, sorghum prefers 70°F to 75°F soil temperatures. Avoid planting biomass sorghum before the last spring frost. If planting a photoperiod-sensitive variety, then plant the biomass sorghum after the acceptable photoperiod. Otherwise, the crop could reproduce early and ultimately yield little biomass.

During planting, target spacing rows from 20 inches to 30 inches. In medium or heavy soils, planting depth should range from 0.75 inches to 1.25 inches. In sandy soil, planting depth may be as deep as 2 inches. Per acre, biomass sorghum seeding rates average 100,000 seeds, but the rate may range from 75,000 seeds per acre to 120,000 seeds per acre.

Management

Soil fertility needs will vary depending on the particular field. However, as a general guide, apply 120 pounds of nitrogen, 65 pounds of phosphorus and 120 pounds of potassium. Of these nutrients, nitrogen deficiency tends to be most common in biomass sorghum production, and its extent depends on biomass removal. Nitrogen needs may range from less than 10 pounds per dry ton harvested to more than 15 pounds per ton.

Relative to switchgrass, a perennial energy crop, biomass sorghum plants on average need less nitrogen, phosphorus, potassium and pesticide per dry biomass ton produced. Because biomass sorghum is an annual, it would need more herbicide and diesel investments per dry biomass ton produced, based on an Environmental Protection Agency analysis.

Weeds, Pests and Diseases

Too much weed presence may hinder biomass sorghum from becoming established and result in poorer biomass yields at harvest. Weed management in biomass sorghum fields should start before planting, especially because sorghum producers have relatively few herbicide control options. Planting biomass sorghum in fields free of weeds will give the crop an opportunity to grow, become established and better compete with weeds. Although pre-planting tillage may help with managing weeds, it may increase erosion potential and land preparation investment. Spraying herbicide as a pre-planting weed burndown may be an alternative. Producers could also consider using a herbicide safener to protect the biomass sorghum crop from herbicide damage.

Pest pressure risk varies by growth stage, plant component and other factors. As seedlings, biomass sorghum may be susceptible to cutworms. Nematodes may harm biomass sorghum roots, greenbugs and fall armyworms may harm leaves and panicles, and sugarcane borers may damage biomass sorghum stalks. Disease presence may vary by geography and management practices. Possible diseases that may influence biomass sorghum include anthracnose, downy mildew and Fusarium. To manage pests and diseases, biomass sorghum seed treatments are options. Rotating crops may also help with pest and disease control.

Harvest and Storage

To harvest biomass sorghum, producers may consider two chief machinery options. First, they could use a forage chopper, or second, they could swath the material into windrows and then bale it or pick up it with a forage chopper.

Harvest timing will vary based on several factors. Planting multiple varieties with different maturities or staggering planting would lengthen the harvest season. If the planted varieties require multiple cuttings, then harvest would occur at certain points throughout the growing season and provide a staggered biomass supply.

Producers may cut sorghum throughout the winter using a silage harvester. Postponing harvest to later times in the season may increase the likelihood for lodging, which may lead to the crop touching the ground, adding grit to the biomass material and possibly reducing biomass quality. If biomass yields are high, then biomass sorghum stalks may lean on other stalks instead of falling completely to the ground.

The decision about harvest timing may also hinge on moisture content. Some varieties may record 80 percent moisture levels, and other varieties may contain less moisture at harvest than other sorghums, such as forage sorghum.

Moisture level preferences may vary by end use. With drier material, harvesting and transportation tend to be less expensive. To manage moisture levels, producers may delay harvest, apply herbicide before harvest, use swathers with conditioning systems or rake and ted biomass sorghum after harvest. Delaying harvest allows the crop to reach maturity and die naturally. A frost can kill the sorghum and help with drying. The ability to postpone harvest will depend on the environment. Exposing biomass sorghum to weather elements as it dries may lead to reduced biomass extractive content, however. Research has focused on whether broad-spectrum herbicide application could kill the crop and facilitate drying. Preliminary results indicate that herbicide application may be a viable approach. Using a conditioning system could help with separating biomass sorghum stalks and improving the drying process. For biomass sorghum in windrows, raking or tedding exposes the biomass sorghum to sun and wind that may help to consistently dry the material. Sorghum and sudangrass crosses tend to dry more easily than biomass sorghum varieties that are sorghum and sorghum crosses.

Storing biomass sorghum has two primary purposes. First, it ensures a consistent, year-round supply for operators. Second, it allows just-in-time inventory conversion facilities to continue operating when other feedstocks may not be available. Stored biomass sorghum may take several forms. For example, biomass sorghum may be ensiled. Producers may bale biomass sorghum material in large square bales or large round bales. Generally, the large square bales would work if moisture levels are less than 20 percent. Transportation and storage would be less efficient for large round bales. Alternatively, biomass sorghum may be stored in module form like cotton modules.

Sources

BioDimensions, Inc. 2012. West Kentucky Agricultural Biomass Pellet Report. BioDimensions, Inc. Memphis, TN 38117.

Blade Energy Crops. 2010. Managing High-Biomass Sorghum as a Dedicated Energy Crop. Ceres, Inc. Thousand Oaks, CA 91320.

Cross, Jennifer. 2014. A New Sorghum For Biofuels. Hay & Forage Grower. Minneapolis, MN 55425.

Environmental Protection Agency. 2014. Notice of Opportunity To Comment on the Lifecycle Greenhouse Gas Emissions for Renewable Fuels Produced From Biomass Sorghum. Justia Regulations. Mountain View, CA 94043.

Grooms, Lynn. 2014. Alternative crops for more than just biofuel. Farm Industry News. Minneapolis, MN 55425.

Jessen, Holly. 2011. Energy Sorghum. Ethanol Producer Magazine. Grand Forks, ND 58203.

Oak Ridge National Laboratory. 2011. U.S. Billion-Ton Update: Biomass Supply for a Bioenergy and Bioproducts Industry. U.S. Department of Energy. Washington, DC 20585.

Retka Schill, Susanne. 2007. Tall Texas Sorghum. Ethanol Producer Magazine. Grand Forks, ND 58203.