Learn About Growing Sorghum: A Natural Sweetener

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Sorghum syrup can be homegrown or purchased as a syrup; it is a great natural sweetener. This tasty product is highlighted in "Sweet Sorghum" by George Kuepper with the Kerr Center for Sustainable Agriculture. His book explains growing sorghum and sorghum production.
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Hand cutting can be done with any tool suitable for severing thick-stalked vegetation. Machetes and corn knives are two of the more effective implements. Some old-time growers use a sharpened hoe attached to a shortened handle.

Covering the modern homesteading tradition of growing sorghum in his book, Sweet Sorghum (Kerr Center for Sustainable Agriculture) George Kuepper discusses ways to transform this natural sweetener from plant to plate. Growing sorghum is a custom in which the product, sweet sorghum, is transformed into a nutritious homemade syrup.This excerpt is from Chapter 10 and describes growing sorghum. Learn how to process your sorghum into sweet sorghum syrup by reading Sorghum Production: Milling and Cooking.

You can purchase this book fromKerr Center Publications: Sweet Sorghum.

Growing Sorghum: 

Variety Selection 

Sorghum is a tropical grass native to Africa. It first came to the Americas with imported slaves. Sorghum resembles corn in many of its characteristics and in the manner it is grown. Sorgo, the term used for sweet sorghum, is only one of several types of sorghum. The sorghum family includes grain sorghums, such as ‘milo’ and ‘hegari’; forages, like ‘sudangrass’ and ‘kafir’; ‘broomcorn’; and ‘Johnsongrass,’ a perennial sorghum.

Also called cane, sorgo is distinguished by the abundance of sweet juice in the stems and typically tall height. Sorgo cane should not be confused with sugarcane, another tropical grass from which a sweet syrup can be made. Several sweet sorghum varieties are currently available. All are open-pollinated or nonhybrid.

They can be divided into traditional and improved categories. Sorghum is drought tolerant, particularly when compared to corn. Yield and syrup quality of any sweet sorghum variety will suffer under a drought, although tolerance will vary.

Traditional varieties have been cultivated for generations and are still grown, almost religiously, by some farmers. When compared to improved types, growing sorghum of older varieties are more prone to lodging and disease. Yields are also lower. High syrup quality, whether real or perceived, is the main reason they are grown. One value of traditional varieties may be in specialty marketing where gourmet tastes are targeted.

While the loyalty of growers to traditional varieties appears to be nothing but nostalgia, these farmers have done the rest of us a favor by preserving raw, genetic material. When new varieties are developed, plant breeders search for desirable genes in commercially available seed and wild relatives. As quality and nutrition become important in gene selection, the diligence of these “hard-headed” folks will be appreciated.

Locating seed from traditional varieties can be challenging. ‘Sugar Drip’ is the only one commonly sold through farm cooperatives and seed catalogues in the mid-southern states. Other traditional varieties include ‘Honey Drip,’ ‘Texas Seeded Ribbon Cane,’ ‘Sart,’ ‘Orange,’ and ‘Black Amber.’ Because so many names have been given to the same varieties over time, one may have difficulty knowing the true identity of the traditional types.

Improved varieties have come from breeding efforts during the last few decades. They are usually high yielding, relatively disease and lodging resistant, and produce high-quality syrups. Disease resistance is an important factor, especially in traditional growing regions and areas where ‘Johnsongrass’ carries maize dwarf mosaic virus. Other diseases of significance are anthracnose, downy mildew, and bacterial leaf diseases.

‘Dale’ is probably the most widely grown of the improved varieties. It is a mid-season variety and widely adapted. ‘M81E,’ released in 1981, is a late-season type. In southeastern Oklahoma, it has produced a syrup somewhat lighter than ‘Dale’, and yields have been comparable. ‘Theis’ is a late-season variety, makes a mild syrup, and grows tall. ‘Brandes,’ somewhat later than ‘Theis,’ has lodging resistance as its strong suit. It is susceptible to drought and should be grown on soils with good moisture-holding capacity. ‘Bailey,’ a release from Georgia, produces good quality syrup only at high elevations. ‘Della’ is the latest improved variety. Developed in Virginia by Robert Harrison, it was released in 1990, and little performance data is available. ‘Della’ is similar to ‘Dale’ but has improved seedling vigor and matures about one week earlier.

Many sorghum varieties are susceptible to damage by cotton insecticides, particularly organophosphates, like methyl parathion. ‘Dale,’ ‘Theis,’ and ‘M81E’ are tolerant to these pesticides. ‘Brandes,’ on the other hand, is easily damaged. One can extend the productive life of a variety using cultural methods that suppress diseases and insect pests and enhance the vigor of the crop. Crop rotation is particularly important, because several improved varieties have become susceptible to diseases that can be controlled by this practice.

Saving Sorghum Seed

Since sorghum is largely self-pollinating and none of the varieties are hybrids, saving seed for planting in later years or for sale is a viable option. In most varieties, the soft-dough stage signals the time for syrup harvest. However, the developing seed is less vigorous than fully matured seed. To overcome this problem, growers leave one or more rows of sorghum specifically for harvesting seed.

If more than one variety is grown in a limited area, cross-pollination is a possibility. While some desirable characteristics may arise, growers are seldom able to capture them. Keeping varieties pure guarantees more predictability in crop performance year to year. To ensure reasonable purity of farm-grown seed, allow at least 650 feet between varieties. More distance is required where prevailing winds increase the likelihood of cross-pollination. Once harvested and cleaned, seed should be put in a tight container and stored in a cool area. A freezer is an excellent place to store sorghum seed. After a number of years, Foundation seed stock should be purchased to certify the purity of improved varieties.

Sweet Sorghum Yields

Yield and quality of sorghum syrup are dependent on many factors: variety, soil type, fertility management, insects, diseases, climate, weather, and cultural practices. While field production of sorgo for syrup is straight forward for those already accustomed to growing grain sorghums or corn, certain points need special attention.

Site and Soil Selection for Growing Sorghum

Well-drained loams and sandy looms are ideal for growing sorghum, although production is done on a much wider range of soils. Poorly drained and clayey soils are not recommended. Shallow soils and soils low in organic matter may cause problems during a drought. Soils high in organic matter, such as mucks, are also not advised, because excessive nitrates lower syrup quality.

Sorghum Crop Rotation

A traditional saying is, “Sorghum is hard on the soil.” There is considerable basis for this belief. It is probably rooted in one or more of the following: fertility depletion, moisture depletion, or nitrogen tie-up. In most harvesting methods, the entire stalk is removed from the field leaving little plant residue. Removing the whole plant takes significant quantities of essential nutrients. The lack of residue also increases the chance of erosion, another factor in soil depletion. A drought tolerant crop, sorghum roots forage the soil more thoroughly for moisture than most row crops. In regions of marginal rainfall or untimely drought, this can affect the following crops and cover crops.

The high sugar content in the roots of sorghum can cause the tie-up of available soil nitrogen by bacteria as they decompose the subsurface residue. The breakdown of sorghum roots in the soil by bacteria requires much nitrogen from the soil-making it temporarily unavailable to the next crop.

A winter cover crop of inoculated legumes, such as vetch, clovers, or winter peas, should follow sorgo. Because sorghum is harvested quite late in the fall, establishing a cover crop may be difficult. Crops planted the next spring or summer will likely be unaffected by moisture depletion unless the winter is exceptionally dry. Spring- and summer-planted, nonleguminous crops should not suffer nitrogen depletion if sufficient time is allowed for decomposition of the sorghum roots and residue. Since moisture depletion and nitrogen tie-up are temporary conditions, their effect on long-term soil fertility relates primarily to the difficulty in establishing winter crops or other soil cover following sorghum. Fertility depletion, however, should be addressed through sustainable farming practices.

Proper crop rotation has long been a means of maintaining soil fertility. It is also a strategy for managing weeds, insect pests, and diseases. In sorghum, crop rotation can help suppress several bacterial leaf diseases, anthracnose, wireworms, and other pests. It is possible to grow sorghum after most crops with the exception of tobacco (Bitzer, 1987). Tobacco is a heavily fertilized crop, and the carryover has a negative effect on syrup quality. Because syrup quality is lowered by excessive soil nitrates, sorgo should not follow leguminous green manure crops or spring-plowed legume forages. Where winter cover crops are plowed down in advance of planting, small grains, other grasses, or brassicas are better than winter legumes. Sorgo has successfully followed corn and cotton (Stokes et al., 1957), small grains, soybeans, spring-planted English peas, southern peas, most vegetable crops, and fallow. Weeds may be a problem when planting sorgo after corn.

Sweet Sorghum Irrigation

Based on the experience of a limited number of growers, sorgo appears to respond well to irrigation. Also, our observations during the 1989 season suggested irrigation may increase juice Brix. The crop forms seed heads in late summer. Moisture stress at this stage results in a type of dormancy. Irrigation or late rains restore plant growth and trigger the development of secondary seed heads. It is unclear to what extent this influences syrup quality, but yield loss is likely due to the dormancy period.

Sweet Sorghum Fertilization

A persistent myth is that good syrup can only be made from cane grown on poor soil. While much research needs to be done, this generalization has not been proven. Research has shown that high soil nitrate has a negative effect on syrup quality. Excessive nitrates in the soil can come from green manures, fresh barnyard manures, or commercial fertilizer. As suggested earlier, not planting forage or plowdown crops of pure legumes will help prevent excess nitrates. Also, while manures may certainly be used for sorgo production, they must be managed properly. Unless well composted, do not spread manures in late winter or spring before planting. According to experienced growers, proper management of poultry manures is especially important. Application and incorporation during the summer or fall of the previous year should provide sufficient time for necessary decomposition and the reduction of nitrate and other salts.

Commercial fertilizers should have a ratio of 1:1:1 and not exceed 50 pounds N on average soils or 40 pounds N on more fertile ground. Do not use nitrogen fertilizers for side-dressing. Organic fertilizers, such as tankage and cottonseed meal, are good starter fertilizers. Sidedressing with organic nitrogen sources is also not recommended. These fertilization guidelines reduce the possibility of excessive soil nitrates. Ideal soil pH appears to range from 6.0 to 6.4. The amount of lime applied should be determined by soil calcium levels and base saturation rather than pH. Avoid using dolomite (high magnesium) lime, because this material often causes soil nutrient imbalances. Farmers may also use colloidal clay phosphate and/or rock phosphate, other rock powders, humates, and basic slag to increase soil fertility for the long term. Their selection and application should be guided by regional availability, soil test results, and comprehensive information on the product being considered. Composted materials are also used to improve fertility. Caution is warranted when dealing with urban and industrial wastes. They may be contaminated with heavy metals, such as lead and arsenic, and should be avoided.

When to Plant Sweet Sorghum

Recommended planting dates for grain sorghum can be used for planting sorgo. Soil temperature should be 65·F or higher. Early planting is not encouraged when the risk of cold, wet weather is significant. Sorgo seed is not vigorous under these conditions, and poor stands can result. Shorter season varieties can be planted late, through June in southern Oklahoma and Arkansas. Planting much later increases the risk of loss to midsummer droughts and early freezes. Late planting also increases susceptibility to diseases.

Seeding Rates and Row Widths of Sorghum Crops

Sorgo can be sown with equipment used for corn, cotton, or grain sorghum production in row widths from 30 inches to more than 40 inches. On-farm research in Alabama tested skip-row planting and had favorable results (Slaten, 1987). It was adopted in a modified form by KCSA. A final stand of two to three plants per row foot is the current recommendation in most areas. Many traditional growers leave as much as 14 inches between plants. Helm and Beasley (1942) suggested leaving 8 to 10 inches. Wide spacing was probably done to reduce labor in hand stripping and harvesting and to increase drought survivability.

Typically, two to four pounds of seed per acre are required. The actual number of seeds per pound varies little from variety to variety. ‘Dale’ has about 26,000 seeds per pound; ‘Sugar Drip,’ 25,000; and ‘M81E,’ around 24,500. Germination tests should be done before planting. Thinning with a hoe to achieve desired spacing and to control in-row weeds is another traditional practice, more common in the days of cheap labor. Hoeing is limited mostly to small plantings and large families. It is best to wait until the plants are about three inches tall. Complete thinning early to avoid root damage to remaining plants. If weeds are a problem, cultivate first. Less time will be spent hoeing weeds that the cultivator may remove.

A farmer from Kentucky, Danny Townsend, proposed the concept of transplanting seedlings as an option for sorghum production at the 1991 NSSPPA meetings. Employing equipment and techniques used for tobacco, transplanting may eliminate early weed pressure.

Sweet Sorghum Weed Management 

Weeds are controlled in sorghum by integrated methods: namely, fertility management, crop rotation, prevention, and cultivation. Many weed problems originate from poor tilth and fertility. Various weeds function in nature to bring soil back into balance by fixing certain nutrients or by aerating the soil. Their presence can actually be used to guide soil management (McCaman, 1985). Some individual weed problems can be managed by proper liming to adjust pH, provide calcium, and stimulate biological life in the soil.

Annual crop rotation controls weeds in large part by alternating the cultural practices and the nature of the competing vegetation. It is especially handy in controlling perennial and biennial weeds. Use cleaned seed for all crops in rotation. When buying seed, read the label for information on weed seed content. Such precautions can keep problem weed infestations isolated and prevent the introduction of new weed species. Also check equipment when driving to different fields for accumulations of weed seeds, roots, or rhizomes. Slow seedling emergence and growth make weed control by tillage difficult in the early part of the year. “Blind” cultivation using harrows and rotary hoes may be risky after germination, because sorghum seed is small and not planted as deeply as corn, soybeans, or sunflower.

Delaying planting until conditions for germination approach optimal is a good strategy. Once cultivation begins between the rows, traditional wisdom advises that it be repeated as soon as possible after each rain. The soil has to be dry enough for working even though many weeds may not be visible. Weeds are most easily killed when young and just emerging. In most cases only shallow cultivation is needed. This is important as the crop matures since root systems can be easily pruned, reducing yield and increasing susceptibility to drought. As the crop grows, tractor speeds can be increased and shallow hillers used to throw soil at the base of the plants to smother weeds in the row. Where perennial weeds, such as quackgrass or bindweed, are problems, deeper tillage using narrow cultivating shoes may be needed. This should be limited to the early part of the season. Cultivate deeply only toward the middle of the furrow. No herbicides are currently labeled for sorgo because of its limited acreage in most states. We encourage growers to try alternatives to herbicides as a general rule. In our opinion, reducing the use of agrochemicals contributes to the long-term sustainability of our agriculture. If circumstances dictate the use of an herbicide or any other pesticide, please read and follow all label directions.

Sorghum Pests

Most insects and diseases can be managed by planting resistant varieties, clean tillage, crop rotation and by controlling alternate-host vegetation, like ‘Johnsongrass.’ Birds are a problem in many areas but only to the seed crop. Among the more effective deterrents are the Avalarm system, which emits a simulated distress cry, and the Scare-eye balloon, which mimics predatory owls.

Harvesting Sorghum: Judging Maturity of Sorghum Crops

The decision to harvest is made after evaluating seed head maturity, juice Brix, crop condition, and maturity dates for specific varieties. Sorghum cane should ideally be harvested at maximum sugar content. Since conditions vary year to year and bottlenecks in processing happen, perfect timing is illusive. Sorghum can hold peak sugar content for one to two weeks. After this point, conversion of sugar to starch accelerates. The farmer can anticipate starch problems when processing overripe sorghum cane.

Most varieties approach maximum sugar yield between mid- to late-dough stage of seed development. Many producers continue to rely on this method for scheduling harvest. Others use refractometers to determine sugar content. Refractometers are hand-held instruments designed to measure the bending or refraction of light rays as they pass through liquids. The greater the amount of dissolved solids in a liquid, the higher the refraction. This is measured on a scale called degrees Brix, or percent dissolved solids.

In performing this test, juice is extracted from several representative stalks in a field and viewed through the refractometer.

Most growers begin harvest at about 16°Brix. Brix readings of more than 20 degrees have been recorded on well managed soils in Georgia and Alabama. A single Brix reading may not be representative of the actual sugar content of the crop at any one time. For instance, if a sample is taken shortly after a rain, the Brix may read low. During a drought, it may register high. Degrees Brix should be monitored with time, taking into account weather conditions before and during the time of plant sampling. Determining the Brix of harvested juice is also of value in predicting syrup yield. Table 2 gives expected syrup yield based on Brix and Baume readings.

Refractometers can be purchased for as little as $150. One is needed to measure juice Brix (0 to 32 percent), and a second one is needed to gauge syrup Brix (45 to 82 percent). More expensive models, designed to measure the full range of Brix, can also be used in the cooking process. This may present a savings when compared to the cost of two refractometers; however, the finer graduations on the wide-range models are often more difficult to distinguish, and accuracy may be sacrificed.

An alternative to the refractometer is the hydrometer, a standard instrument used to measure the density of liquids. It works on the principle that objects will float higher in a liquid with a high percentage of dissolved solids. Hydrometers are usually calibrated in the Baume scale. They are slower and more clumsy to use than refractometers and less precise. Hydrometers will not work well in heavy, thick liquids, like finished sorghum syrup. Also, hydrometers containing mercury are prohibited in the manufacture of food by the Food and Drug Administration (FDA).

Stripping and Topping Sorghum Cane 

Many old-time sorghum cooks insist that quality syrup can only be made if all leaves are removed or stripped from the stalk before milling. This probably remains the single greatest conflict among producers today. Supporters have argued that milled leaves contribute undesirable taste and color to the final product. Stripping leaves has benefits including:

1. More crop residue remaining on the field.

2. Less tonnage in hauling, milling, and handling waste.

3. Higher juice recovery during milling.

4. Less filtration and settling required.

5. Great physical exercise.

While many producers have talked about designing mechanized stripping equipment, we are not aware of any. Stripping leaves remains a highly labor-intensive activity. Traditional leaf stripping is usually accomplished by equipping field workers with lightweight wooden “swords,” which are used to strike the leaves from the stalk. Under optimal conditions, two to four strikes per plant removes most leaves. According to the literature, one person may strip from 1/5 to 1/2 acre per 8 hour day depending on plant population, stamina, and enthusiasm.

Removal of seed heads is also an important task in sorghum cane harvest. Seeds clog the strainers at the mill and can cause an unacceptable flavor. Since the top internode (peduncle) contains considerably less sugar than the remainder of the stalk, it should also be removed.

A traditional method in hand-harvest systems involves laying the bundled or loose cane in a uniform row on a truck or wagon, with the seed heads extended over the edge. A chain saw or gas-powered hedge trimmer can then cut off the seed heads. When row binders or choppers are used, powered sickles, rotary mowers, and small bushhogs can be mounted on adjustable-height, front-end loaders to trim the seed heads immediately in front of the binder. The modified Hi-Boy trimmer is another application of this method.

Cutting Sorghum Cane 

The optimum cutting height for sorghum cane is about six inches above the ground. Cutting methods range from labor-intensive hand cutting to mechanized forage heads mounted on choppers or field mills. Hand cutting can be done with any tool suitable for severing thick-stalked vegetation. Machetes and corn knives are two of the more effective implements. Some old-time growers use a sharpened hoe attached to a shortened handle. A novel concept features a sharp knife attached to a stirrup, allowing the worker to hold the cane while cutting the stalks with a kick. Hand cutting has been done in two or three person teams. One or two people hold the stalks while another cuts the cane using a long-handled pole with a hooked blade at the end or a fulI-length, sharpened hoe. Estimates for one person hand cutting an acre of sorghum cane vary from 15 to 21 hours depending on the reference. A horse-drawn tool employed in the past for cane and corn harvesting consisted of a small sled with a seat in the center. Large, winged blades set on the sides cut a row of cane as the sled was drawn alongside. The rider would catch the cane across his or her arm until a suitable amount had collected. This was then dropped to the side.

More common today in both horse-drawn and tractor operations is the use of vertical row binders. Patented by A.S. Peck of Geneva, Illinois, in 1892, these implements have been used to cut and bundle-tie sorghum and corn. Binders may be powered by tractor pto or by a ground driven “bull wheel.” Binders having a bull wheel were designed for draft animals. Manufacturers developed two basic types of heads for these machines, long and short. Binders had either bundle carriers, which dropped the bundles on the ground and away from the next row or bundle elevators, which carried the bundles to a wagon where they were stacked by hand.

Like sorghum mills, vertical row binders are now archaic technology. No major company continues to make these machines, and replacement parts are difficult to find. At KCSA several scrap binders were bought for parts to keep others operating. Farmers who have experience in running and maintaining such equipment are the best sources of information. Information can also be found in used book stores or in reprints and articles in current, popular journals. Many of these binders were intended for draft animals, and they should be handled accordingly. Horse-drawn implements were designed to withstand the stresses and speeds associated with draft animals, not high-powered tractors. If attached to a tractor, horse-drawn equipment will last longer if treated with this in mind.

Large-scale production systems require more mechanization. Because sorghum machinery is scarce, farmers have taken the initiative and created what they needed. Forage harvesters, for example, have been converted into sorghum cane harvester/choppers. The harvesters’ field chop the cane, which is then hauled to a stationary mill. The plant material is run through a shakerblower to remove leaves and other chaffy debris before milling. One homemade unit incorporates the shaker-blower and the mill as part of a self-propelled machine. Another option bypasses the chopper entirely. After cutting, the stalks are immediately fed into rollers. Because green leaves are also milled, questions of syrup quality have been raised. Considerable detail on these harvesters is given in “Single-Pass Harvesting of Sweet Sorghum” (Miller et al., 1990).

Handling Sorghum Stalks

Generally, any activity that breaks the rind of the stalk will cause loss of juice and increase handling difficulty. Reasonable care should be taken to avoid driving over bundles or damaging the stalks in any way.

Whether stripped or not, stalks can be stored seven to ten days following cutting with no loss of syrup yield or quality. This delay may actually enhance syrup quality, because desirable enzymatic changes happen within the stalk. These changes involve the action of naturally occurring invertase. Invertase breaks down sucrose into simple sugars, preventing crystallization of the syrup. Allow at least three days between cutting and milling, particularly when the cane is unstripped.

The weather influences the way cane is handled between cutting and milling. Rain-soaked cane can have quality problems. Many producers report darkened syrup from wet cane. When leaves are left intact, molds and stalk and leaf rots are a possibility. This is especially true if hauling and milling are delayed.

This excerpt has been reprinted with permission from Sweet Sorghum by George Kuepper, published by Lara M. Ervin, 1992.

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