Grain Sorghum (Milo)

P. R. Carter1, D. R. Hicks2, E. S. Oplinger1, J. D. Doll1, L. G. Bundy1, R. T. Schuler1, and B. J. Holmes1

1Depts. of Agronomy, soil Science, and Agricultural Engineering, Cooperative Extension Service and college of Agricultural and Life Sciences, University of Wisconsin-Madison, WI 53706.
2Dept. of Agronomy and Plant Genetics, University of Minnesota, St. Paul, MN 55108.
November, 1989.

I. History:

Farmers on the hot, dry plains from Texas to South Dakota grow and use grain sorghum like Corn Belt farmers use corn. Large acreages of grain sorghum are also grown in Africa and Asia in areas where the climate is too hot and dry for corn.

During the past 25 years, the grain sorghum acreage in the U.S. has ranged from 15 to 18 million acres per year. Grain sorghum acreage is somewhat greater than acreages for oats and barley, but considerably less than the land area planted to corn, wheat, and soybeans.

In cooler, more humid regions, corn is usually a better choice than grain sorghum, but renewed interest in grain sorghum occurs whenever hotter and drier than normal growing seasons are experienced.

II. Uses:

Worldwide, sorghum is a food grain for humans. In the United States, sorghum is used primarily as a feed grain for livestock. Feed value of grain sorghum is similar to corn. The grain has more protein and fat than corn, but is lower in vitamin A. When compared with corn on a per pound basis, grain sorghum feeding value ranges from 90% to nearly equal to corn. The grain is highly palatable to livestock, and intake seldom limits livestock productivity. However, some sorghum varieties and hybrids which were developed to deter birds are less palatable due to tannins and phenolic compounds in the seed. The grain should be cracked or rolled before feeding to cattle; this improves the portion digested.

Pasturing cattle or sheep on sorghum stubble, after the grain has been harvested, is a common practice. Both roughage and dropped heads are utilized. Stubble with secondary growth must be pastured carefully because of the danger of prussic acid (HCN) poisoning.

Grain sorghum may also be used as whole-plant silage, however another sorghum, sweet sorghum, was developed as a silage crop. Sweet sorghum produces much higher forage yields than grain sorghum, but feed quality will likely be lesser because there is no grain. Some growers mix grain sorghum with soybeans to produce a higher protein silage crop.

III. Growth Habits:

Grain sorghum is a grass similar to corn in vegetative appearance, but sorghum has more tillers and more finely branched roots than corn. Growth and development of sorghum is similar to corn, and other cereals. Sorghum seedlings are smaller than corn due to smaller seed size. Before the 1940s, most grain sorghums were 5-7 feet tall, which created harvesting problems. Today, sorghums have either two or three dwarfing genes in them, and are 2-4 feet tall. While there are several grain sorghum groups, most current grain sorghum hybrids have been developed by crossing Milo with Kafir. Other groups include Hegari, Feterita, Durra, Shallu, and Kaoliang.

The grain sorghum head is a panicle, with spikelets in pairs. Sorghums are normally self-fertilized, but can cross pollinate. Hybrid sorghum seed is produced utilizing cytoplasmic male sterility. Sorghum flowers begin to open and pollinate soon after the panicle has completely emerged from the boot. Pollen shedding begins at the top of the panicle and progresses downward for 6-9 days. Pollination normally occurs between 2:00 and 8:00 a.m., and fertilization takes place 6-12 hours later.

Sorghum can branch from upper stalk nodes. If drought and heat damage the main panicle, branches can bear panicles and produce grain. The grain is free-threshing, as the lemma and palea are removed during combining. The seed color is variable with yellow, white, brown, and mixed classes in the grain standards. Brown-seeded types are high in tannins, which lower palatability. Percentages of the seed components, endosperm (82%), embryo (12%), and seed coat (5-6%) are similar to corn.

IV. Environment Requirements:

A. Climate:

Low temperature, not length of growing season, is the limiting factor for production in most of the Upper Midwest. Average temperatures of at least 80° F during July are needed for maximum grain sorghum yields, and daytime temperatures of at least 90° F are needed for maximum photosynthesis. For example, normal average temperatures for July are about 75° F in southern Wisconsin. Night temperatures below 55° F for a week at the heading and pollination stage may result in heads with very little grain. Normal night temperatures during August range from about 65° F in southern to 60° F in central Wisconsin. In September, the range is from 55° F in southern to 50° F in central Wisconsin. In southern and central Minnesota, July and August temperatures are similar to those for southern Wisconsin. Therefore, low temperatures may prevent successful production of grain sorghum in central and northern Wisconsin and Minnesota or as a late-planted emergency grain crop in southern Wisconsin and Minnesota. Plants should complete heading by early August to insure excellent grain set.

Soil temperature at planting time is critical for grain sorghum. Sorghum seed needs soil temperatures of 60-65° F for good emergence.

Three characteristics of sorghum give it a potential advantage over corn in dry areas:

1. Corn is cross-pollinated. Severe drought at silking time may cause barren ears (no kernels). Sorghum is self-pollinated and produces heads over a longer time period because tillers develop over several weeks. Consequently, short periods of drought do not seriously damage pollination and fertilization. In a longer drought, sorghum produces fewer and smaller heads but they are rarely without kernels.

2. An optimum relationship between plant population and moisture supply is often critical with corn but unimportant with sorghum. When soil moisture is plentiful, sorghum heads grow large and tillers produce heads. But if drought occurs, heads are small and fewer tillers develop. Consequently, sorghum growers can plant high populations for potentially high yields. Corn growers can choose between high populations for maximum yields or lower populations with less chance of serious loss from drought.

3. Sorghum foliage resists drying. At equal moisture stress, corn leaves lose a greater percentage of their water content than do sorghum leaves. The waxy coating on sorghum leaves and stems may be an important cause. This coating often gives the leaf sheaths a sticky, frosty appearance.

B. Soil:

Sorghum is more tolerant of wet soils and flooding than most of the grain crops--an interesting phenomenon in relation to its drought tolerance. However, most of the poorly drained, wet soils in Wisconsin and Minnesota are too cold for grain sorghum.

V. Cultural Practices:

A. Seedbed Preparation:

A seedbed similar to the one prepared for corn is also good for grain sorghum. The use of a cultipacker or corrugated roller after seeding often gives better stands. In warmer regions, reduced- and no-tillage systems are used for grain sorghum. Soil temperatures may be toocold for these systems in much of the Upper Midwest.

B. Seeding Date:

Grain sorghum should be planted when soil temperatures reach 60 to 65° F. Generally this is 15 to 20 days after corn planting or between May 15 and early June. Grain yields decrease as planting is delayed after early June. Most hybrids require 90-120 days to reach maturity, therefore late-planting as an emergency crop is not recommended.

C. Method and Rate of Seeding:

1. Method of Planting: Plant grain sorghum in rows at a depth of 1 inch in heavy soil and 1 1/2 to 2 inches in sandy soil. Corn planters are probably the most common seeding equipment. It is important to place the seed in moist soil to obtain fast emergence of the seedling.

A grain drill can also be used to plant the seed in narrow rows. Some adaptations in the grain seedbox may be necessary to isolate the seed above the hole. Some growers have attached small gas funnels above the holes in the seedbox and place the seed in the funnels. Commercial equipment is also available for most newer drills.

2. Rate of Planting: Seed size will influence the pounds of seed to plant per acre. As a general rule, there are approximately 16,000 sorghum seeds per pound. Most sorghum hybrids average about 75% emergence. On soils of good fertility and adequate moisture, the recommended rate of seeding is 8-10 pounds of seed in rows of 30-40 inches in width. At this rate of planting, seeds will be 1 to 1 1/2 inches apart in the row with a population of 100,000 to 120,000 plants per acre.

On soils that are less fertile or more droughty, the seeding rate should be 5-6 pounds per acre.

3. Row width: The row width used will likely depend on the equipment available. During the last few years, there has been considerable interest in planting grain sorghum in narrow rows to boost grain yields. With narrow rows, greater distance between plants in the row must be planned in order to get the optimum plant population per acre. The main advantage of narrow rows is to attain more efficient use of moisture, soil fertility, and sunlight. Grain yields in Minnesota studies were 10-15% higher in 10-inch rows than in 40-inch rows. The primary disadvantage is that cultivation is not possible and weed control is dependent entirely on chemical herbicides.

D. Fertility and Lime Requirements:

Nutrient needs of sorghum closely resemble those of corn in that sorghum uses relatively large amounts of nitrogen and moderate amounts of phosphorus and potassium. The grain in a 100-bushel per acre grain sorghum crop removes about 100 lbs. of nitrogen, 14 lbs. of phosphorous, and 14 lbs. of potassium.

A soil test is the most practical method of determining fertilizer needs. Apply phosphate and potash according to soil test recommendations where soil tests for P and K are low (L) or very low (VL). Use the nitrogen and maintenance phosphate and potash recommendations shown in Table 1. Lime soils to a pH of 6.0 to 6.5.

Table 1: Annual nitrogen, phosphate, and potash recommendations for grain sorghum.
  Nitrogen recommendation
organic matter %
Phospahate and Potash recommendation1
bu/a <2 2-5.0 5.1-10 >10 P2O5 K2O
50 to 100 120 100 80 60 30 30
1Amounts shown are for medium (M) soil test levels. Apply 50% of this rate if soil test is high (H) and omit if soil test is excessively high (EH).

Nitrogen can be applied in the spring as a preplant application, at planting, or as a side dressing at cultivation. Appropriate N credits should be taken for manure and previous legumes to reduce N fertilizer rates. A starter fertilizer may be beneficial.

E. Variety Selection:

Improved short-season grain sorghum hybrids are available, but most of the breeding is for the major grain sorghum production areas, which have warmer, longer growing seasons.

Hybrid trials are not conducted in Wisconsin, but results of limited Minnesota trials are reported in Miscellaneous Report 24. Hybrids listed in this publication may be of acceptable maturity for southern Wisconsin and sandier, warmer soils in central Wisconsin. Hybrid trials are also conducted in Iowa, but these focus on the drier, warmer western and southern portions of that state.

F. Weed Control:

Early spring seedbed preparation followed by one or two shallow cultivations, just before planting sorghum will kill several generations of weed seedlings and give sorghum a chance to get ahead of the weeds. Timely cultivations of sorghum planted in 20-inch or wider rows during the early growing stages are highly important. Sorghum planted in narrow rows can not be cultivated, but it is a highly competitive crop and can dominate many weeds. Several herbicides are available to compliment cultural and mechanical practices. Quackgrass can be controlled with 1 qt/A of Roundup applied when the weed is actively growing and has 3 to 4 leaves. Other perennial weeds such as Canada thistle, milkweed and hemp dogbane should be suppressed the year before sorghum is planted.

Several selective herbicides can be used in sorghum. Atrazine can be applied as a preplant incorporated, preemergence or postemergence herbicide. Application rates are similar to those used in corn, as are the concerns of atrazine carryover. If crops other than corn will be planted next year, do not use atrazine in sorghum. On the other hand, sorghum could be safely planted in fields with atrazine residues from previous years.

Dual and Lasso can be used as a preplant or preemergence treatment only when sorghum seed is treated with a safener. Your seed dealer may be able to obtain safener-treated seed for you. Dual and Lasso are excellent annual grass herbicides and could be used in combination with atrazine. If incorporated into the upper 2 inches of soil, they suppress yellow nutsedge.

Ramrod is chemically related to Lasso and Dual but can be used preemergence in sorghum without a chemical safener applied to the seed. It controls many annual grasses and can be mixed with atrazine to control a broader spectrum of weeds.

Buctril, Banvel and 2,4-D are labeled for use in grain sorghum for postemergence broadleaf weed control. Their use directions and rates are similar to those for corn.

G. Diseases and their Control:

A seed treatment such as Captan should be used to control seed rots and seedling blights. Leaf diseases can be problems in areas with high rainfall and humidity, but generally do not cause serious losses. Planting resistant hybrids, providing optimum growing conditions, rotating with other crops, removing infested debris, planting disease-free seed are all methods which can be used to minimize losses from disease.

H. Insects and Other Predators and their Control:

Under Minnesota and Wisconsin conditions, the most serious pest problem for grain sorghum growers is likely to be bird damage. Planting larger fields in one block and locating these away from urban areas or farm buildings may help reduce the problem.

Grain sorghum is resistant to corn rootworms, but may be attacked by corn earworms, aphids, and greenbugs.

I. Harvesting:

Nearly all grain sorghum is harvested as a standing crop with a combine. Combining time will depend on the fall weather and the availability of grain drying facilities. Sorghum grain can be threshed free of the head when the seed moisture is 20-25 percent. The seed is hysiologically mature at even higher moisture levels. Frost will generally kill the top of the plant and help to lower the moisture content. Some hybrids have a loose, open type head which astens field drying.

Sorghum seed is easily damaged in the threshing operation, especially when the grain is dry. The combine platform should be operated as high as possible to minimize the mass of stems entering the combine. If necessary, the cylinder speed can be reduced to one-half that used for wheat to prevent cracking the seed. However, grain moisture will normally be higher and faster cylinder speeds can be used. The recommended cylinder speed is 750-1300 R.P.M. but loss determinations should be made to refine the combine adjustments. An average loss of 19-22 kernels per square foot is equal to one bushel per acre loss.

The grain sorghum crop can be harvested for high-moisture grain silage. When fed to livestock, its digestibility will be increased by grinding or rolling. High moisture grain sorghum can be combined and ensiled when the grain is about 25-30% moisture.

J. Drying and Storage:

Grain sorghum can be dried with corn drying equipment. However, because the grain is smaller in size, fans may need to be operated at higher static pressure than used for corn. Also, grain sorghum needs to be somewhat drier than corn for safe storage since there is less air movement through the grain. Grain should be stored at 13% moisture and in clean bins. The grain should not be heated over 200° F since feeding values are reduced by high temperature.

VI. Yield Potential and Performance Results:

Grain sorghum yields exceeding 100 bushels per acre have been obtained in Wisconsin (Table 2). Yield potential and economics of grain sorghum must be compared to corn to determine whether or not grain sorghum offers an advantage.

On very droughty soils, or if subsoil moisture is very low, grain sorghum may out yield corn. This occurred at the Hancock Research Station in 1971 and 1972 (Table 2). However, when conditions are more favorable for corn production, corn yields will probably be at least 15-20% higher than for grain sorghum. This assumes that planting dates and hybrid maturities are optimum for both crops, with the optimum date for grain sorghum being later than for corn.

Table 2: Performance of grain sorghum compared to corn at three Wisconsin locations, 1971-1972.
  Hancock (sand) Janesville (slit loam) Lancaster (silt loam)
  --------------- Bushels/acre ---------------
Corn 53 111 118
Grain Sorghum 75 93 105

When expected corn yields are less than 50-75 bushels per acre, and the reason for the low yields is moisture stress, grain sorghum may equal or exceed corn grain yields. However, if corn yields greater than 75 bushels per acre are anticipated, grain sorghum is unlikely to be competitive.

VII. Economics of Production and Markets:

The cost of grain sorghum production is about the same as for similar grain-yield production levels for corn. Therefore decisions to grow grain sorghum depend primarily on relative yield potential compared to corn, and the ability to obtain markets. Since market outlets for grain sorghum are not established in most areas of Minnesota and Wisconsin, local elevators will probably not buy it. On-farm utilization as feed is the most likely alternative available to most growers.

VIII. Information Sources:

Robinson, R.G., W.W. Nelson, J.H. Ford, and D.P. Warnes. 1977. Drought and Grain Sorghum. Misc. Report 147, Minnesota Agr. Exp. Station.

Oplinger, E.S. 1973. Grain Sorghum Production in Wisconsin. Field Crops 24.4. Univ. of Wis. Agronomy mimeo. 8p.

Oelke, E.A. 1971. Grain Sorghum in Minnesota. Crop News No. 12, Agronomy and Plant Genetics, Univ. of Minn.

Varietal Trials of Farm Crops. (current year). Minnesota Report 24, Minn. Agr. Exp. Station, p. 13.

Grain Sorghum Performance Tests. (current year). Iowa State Univ. Coop. Ext. Serv. Pub. AG 16-7.

Vanderlip, R.L. How a Sorghum Plant Develops. 1972. Kansas State Univ. Coop. Ext. Serv. Pub. C-447.

Taylor, R. W. (ed). 1988. Grain Sorghum : A Manual for Production and marketing. Extension Bulletin 148, Delaware Cooperative Extension.

Grain Sorghum Production Handbook. 1987. Bulletin C-687, Cooperative Extension Service, Kansas State University.

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