Sorghum

Last updated on August 23, 2012

Note: This information was developed from lecture notes for the Farm and Industry Short Course at the University of Wisconsin.

GENUS & SPECIES

  • All sorghums are now classified as Sorghum bicolor Moench
  • All sorghums are annuals
  • All sorghums are diploids with 10 pairs of chromosomes per nucleus (2n = 20)

DISTRIBUTION

  • Most sorghum is grown where the climate is too hot and dry for CORN
  • The largest acreages are in ASIA and AFRICA, but the greatest production is the the USA (p 4-2, GCM)
  • Very little sorghum is grown in EUROPE and RUSSIA because their climates are too cool for sorghum
  • Generally grown from the tropics to latitudes as high as 45o North and South

During the past 25 years, the sorghum acreage in the US has ranged from 15 to 18 million acres/year. This means that the sorghum acreage in the US is somewhat greater than the acreages of oats and barley, but considerably less than acreages of CORN, WHEAT, and SOYBEANS.

In the US, sorghum is grown primarily in the SOUTHERN GREAT PLAINS

LEADING STATES:

  • TEXAS KANSAS 2-4 million acres/yr
  • NEBRASKA MISSOURI OKLAHOMA SOUTH DAKOTA 1/2 to 1 million acres/year

ADAPTIVE FEATURES

Like corn, sorghum is a C4 species and is a high dry matter producer

Sorghum's most outstanding characteristics are HEAT and DROUGHT tolerance

  • Requires warm days and nights for high yields
  • In the Southern Great Plains, highest yields are usually obtained when the mean temperature for July is in the 80-85oF range.
  • If the average July temp is below 75oF, yields won't be high

Sorghum is slightly more tolerant of both acid and alkaline soils than corn pH 5.5 - 8.5

Like corn, sorghum is a short-day plant. Most hybrids are photoperiod sensitive, but some daylength-insensitive hybrids are being developed

Sorghum is resistant to both CORN ROOTWORMS and CORN BORERS.

USE of Sorghum (grain)

Worldwide, sorghum is a FOOD GRAIN About 3/4 of the world's production is used as food for humans Sorghum is a principal food source in parts of Africa, India, and China 4

In the US, sorghum is used primarily as a FEED GRAIN

In the SOUTHERN GREAT PLAINS, sorghum is an excellent crop for meeting both GRAIN and ROUGHAGE requirements for livestock.

Sorghum is very close to corn in FEED EFFICIENCY for most types of livestock.

CLASSIFICATION of Sorghums 

GRAIN SORGHUMS

  • While there are seven grain sorghum groups, most current sorghum hybrids have been developed by crossing MILO with KAFIR
  • Most sorghum hybrids have either 2 or 3 dwarfing genes in them, are 3 to 4 ft in height, and are easy to combine
  • Prior to 1940's, most sorghums (grain) were 5 to 7 ft in height, which created harvesting problems

SWEET SORGHUMS and GRASS SORGHUMS are grown for hay, silage, or pasture

BROOMS are made from BROOM CORN, which is another type of sorghum BROOM CORN grows 8 to 10 ft in height

BOTANY OF SORGHUM

Vegetative CHARACTERISTICS

  • Sorghum is an annual that is similar to CORN
  • Sorghum stalks have more sugar than corn stalks
  • Sorghum tillers more than corn

Root characteristics

  • Sorghum has a fibrous root system that is similar to corn:
  • Seminal roots
  • Crown roots
  • Brace roots
  • However, there are differences between sorghum and corn
    • Sorghum roots are MORE FINELY BRANCHED than corn roots
    • Sorghum has about twice as much root branching as corn.
    • Therefore, sorghum's root system is considered to be twice as efficient as corn in absorbing moisture from a given volume of soil.
    • Sorghum roots usually don't penetrate as deeply into the soil as corn roots
    • SORGHUM 3-4' CORN 5-6'

INFLORESCENCE

  • The sorghum head is a PANICLE
  • Spikelets occur in pairs (same as tassel and ear of corn)
    • One member is SESSILE, while the other is PEDICELLATE
    • The SESSILE spikelet is fertile and the PEDICELLATE spikelet is sterile
  • Grain sorghum is free-threshing (lemma and palea are removed during combining)
  • Some types of sorghum are not free-threshing - Broom corn - Grass sorghums
  • Many sweet sorghums
  • Seed color is variable.

The Grain Standards book classes sorghum seeds as:

  • Yellow
  • White
  • Brown: high in tannins, which lower palatability
  • Mixed

Percentages of sorghum seed components (endosperm, embryo, and pericarp) are very similar to corn

POLLINATION

  • Sorghum flowers begin to open and pollinate soon after the panicle has completely emerged from the boot Pollination begins at the top of the panicle and progresses downward for 6-9 days
  • Pollination normally occurs between 2 and 8 A.M., but is delayed by cool temp's
  • Early pollination is one of the reasons why sorghum has excellent heat and drouth tolerance
  • Fertilization takes place 6-12 hrs after pollination
  • Sorghums are normally self-fertilized, but they can outcross very easily

GROWTH AND DEVELOPMENT

Growth and development of sorghum is similar to corn, with several exceptions

  • Sorghum seedlings are proportionately smaller than corn seedlings-due to small seed size
  • Sorghum has a lower concentration of LEAF juices than corn, but the STALK, CROWN, and ROOT juices are higher in SORGHUM than in corn
  • Sorghum leaves wilt more slowly than corn leaves because sorghum has a thicker wax coating (cuticle) covering the epidermis
  • As a result, sorghum has a LOWER TRANSPIRATION rate and a slower drying rate than CORN.
  • This permits sorghum to withstand DROUGHT longer than corn
  • Sorghum plants suffering from drought can become dormant and then resume growth when moisture becomes available. Not so with corn
  • Sorghum can branch from its upper stalk nodes. If drought and heat ruin the main panicle, branches can bear panicles that ripen and produce grain

CULTURE AND MANAGEMENT

Sorghum in crop rotations

  • Sorghum readily follows other crops in rotations, but crops following sorghum may have problems, especially if a winter grain is planted shortly after sorghum is harvested in the fall
  • Dryland sorghum depletes soil moisture more than other crops
  • Irrigated sorghum depletes soil N extensively
  • When sorghum stalks are plowed under, soil N can be tied up for a period of time
  • Sorghum stalks are high in sugar (C). Microbes feed on the sugars, and the stimulation of microbial activity increases the amount of N required by the microbes. Until the C:N balance is restored to normal, microbes will compete with growing plants for available N.

Response to irrigation: 

Sorghum responds to irrigation, but usually not as well as corn. In areas where both corn and sorghum are grown, sorghum yields more grain than corn if moisture is limiting, but not if moisture supplies are good throughout the season

Response to fertilizer

  • In irrigated conditions sorghum responds very well to fertilizer (especially N), but in dryland conditions sorghum may not respond very well if moisture is more limiting than soil fertility

PLANTING TIME

  • Sorghum requires a warmer seedbed than corn
  • soil should be at least 60oF at 2" depth
  • In areas where both corn and sorghum are grown, sorghum is usually planted 1 to 2 weeks after corn is planted
  • Sorghum usually is planted in rows with corn planting equipment. Plant population decisions are affected by tillering capacity of the sorghum hybrid

HARVEST

  • Drydown is usually not a problem in the SOUTHERN GREAT PLAINS, but can be a serious problem in northern states such as Wisconsin
  • Sorghum is usually harvested when kernel moisture ranges from 18 to 25%

PRUSSIC ACID POISONING

  • Young sorghum plants, particularly the leaves, contain a substance called DHURRIN, which breaks down to form PRUSSIC ACID (= Hydrocyanic acid = HCN)
  • Prussic acid is poisonous to RUMINANT livestock (cattle, sheep, goats)
  • Losses from grazing occur in the SOUTHERN GREAT PLAINS each year Prussic acid content decreases as the plant matures.

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