Sorghum - planting information

Varieties

For information on varieties please see local resellers or company websites.

Time to maturity

As a general rule, medium-late maturing sorghums are higher yielding - particularly under conditions of good moisture and nutrients. However, as moisture conditions become more limiting, the earlier-maturing hybrids will have greater yield reliability. Hybrids with medium to medium-quick maturity are likely to flower in 60-65 days when sown early, and 50-55 days when sown later under higher temperatures. Slower-maturing hybrids will generally give higher yields than quick-maturing hybrids when moisture and nutrients are not limiting. When moisture is limiting, the quicker-maturing hybrids may offer better reliability. The choice of maturity will therefore depend on conditions at planting (e.g. soil type, stored water) and attitude of the grower to risk.

Midge rating

All commercial sorghum hybrids are tested by DEEDI with support from GRDC and are assigned official midge resistant (MR) ratings from 1-7. Ratings range from 1 (no resistance) to 8+ (practical field immunity)

 Hybrid  MR Rating  Seed Company
 Enforcer  6  HSR Seeds
 Pacific MR 32  6  Pacific Seeds
 MR - Striker  6  Pacific Seeds
 MR  Eclipse  6  Pacific Seeds
 MR - Bazeley  6  Pacific Seeds
 Dominator  5  HSR Seeds
 Venture  5  HSR Seeds
 Pacific MR 43  5  Pacific Seeds
 86G56  5  Pioneer
 84G99  5  Pioneer
 Liberty White  4  HSR Seeds
 MR - Buster  4  Pacific Seeds
 84G22  4  Pioneer
 85G08  4  Pioneer
 Tiger  3  HSR Seeds
 MR - Maxi  3  Pacific Seeds
     

Height

Taller varieties are often higher-yielding but may be more prone to lodging. Hybrids sold in Australia are not excessively tall so height is not a major consideration.

Head type

Open-headed hybrids are desirable in the more humid regions and in areas where sorghum caterpillars are expected to be a problem.

Other diseases (e.g. head smut, leaf blight, grey leaf spot, anthracnose and Johnson grass mosaic virus) can have an effect on yield. Head smut is more likely to be a problem in early planted crops on the Darling Downs and northern New South Wales. The other diseases are more likely to cause problems in later planted crops. More information on these diseases is available from the seed companies.

Rust reaction

Leaf rust can have a significant effect on grain yield, plant death and lodging so rust-resistant hybrids should be used for later plantings when rust infection can be severe. Early plantings are rarely affected by the disease.

Other diseases (e.g. head smut, leaf blight, grey leaf spot, anthracnose and Johnson grass mosaic virus) can have an affect on yield. Head smut is more likely to be a problem in early planted crops on the Darling Downs and northern New South Wales. The other diseases are more likely to cause problems in later planted crops. More information on these diseases is available from the seed companies.

Resistance to ergot

There are no known clear varietal differences for ergot resistance in commercial varieties sown at recommended times. However, there are some hybrids that produce poor quantities of pollen (and are therefore more susceptible to the disease) if flowering during cool conditions. There is a potential benefit in selecting quicker, low-tillering varieties that are not severely affected by cool conditions if sown late.

Grain colour

It is well established that the colour of the pericarp (outer coat of the grain) - whether it is white, cream, red or bronze - has no effect on the feed value of grain sorghum. White, cream and yellow grains are more susceptible to weathering. Such hybrids should not be planted in the humid coastal regions.

The colour of the grain endosperm, white (clear), heteroyellow (one parent yellow endosperm) or yellow, may have an effect on feed value but world literature is not conclusive on this point. Individual seed companies may have information on this for their specific hybrids.

Standability (lodging resistance)

Lodging is a major problem in many grain sorghum producing areas. The most common cause is moisture stress during grain filling, which causes plant death and may be associated with the development of fungal stalk rots.

Lodging occurs frequently enough on most soils to require the use of hybrids with lodging resistance. Only on deep clay soils with good water reserves or under full irrigation should sorghum hybrids without lodging resistance be considered.

Hybrids with 'staygreen' will improve lodging resistance. 'Staygreen' is a plant characteristic that results in less plant death (so less lodging) caused by moisture stress during grain filling. 'Staygreen' also increases yield and grain size under drought conditions.

 

Planting sorghum

Planting time usually varies from September to January, depending on planting rains and soil temperature early in the season.

Crop failures are likely in central and southern regions from very early plantings in August-September and very late plantings in February-March due to cold conditions. Planting at the early end of the range is preferred to avoid midge problems and to allow the option to double-crop a winter crop if sufficient rainfall is received.

Best yields usually follow October plantings. These crops usually miss insect damage by midge. With late crops, midge will need to be managed by selecting midge-resistant sorghum hybrids and/or with the use of insecticide sprays. Generally, mid-season hybrids are the best overall performers.

Sorghum ergot disease risk can also be minimised by planting from mid-October to mid-January in southern Queensland so that flowering occurs between mid-December and mid-March, when the probability of ergot developing in sorghum florets is lowest. See sorghum pests and diseases for more detail on this disease and its management.

In central Queensland, use quick-maturing hybrids for rain-grown spring plantings. For the main summer planting (late December to mid-February), plant slow-maturing hybrids early and the quicker-maturing hybrids later to improve yield reliability.

Soil temperatures

Aim for 15°C and rising. At 15°C sorghum takes 11-14 days to emerge. At 17°C it takes only 7-10 days.

Plant population

Dryland

Expected yields largely determine the population required. Lower populations are required in the marginal areas and high populations where conditions are good.

Planting population - dryland
Yield expectation (t/ha) Plants/ha

1-3

30,000-50,000

3-5

50,000-75,000

5-7

75,000-150,000

Quick-maturing hybrids planted in good conditions require higher plant populations than slower hybrids to realise the yield potential for a particular environment.

Irrigated

In irrigated crops, the choice of target plant population is dependent on row spacing. Increase populations to 150,000-200,000 plants/ha for partial irrigation, or 220,000-250,000 for full irrigation.

Planting population - irrigated
Row spacing (m) Plants/ha

0.15-0.30

250,000

0.75

150,000

1.0 (single rows)

120,000

1.0 (twin rows)

200,000

Average seeding rate

  • dryland 3-4 kg/ha
  • irrigated 10 kg/ha.

The rate depends on seed size, target population, expected establishment and germination percentage.

How to calculate planting rate (kg/ha)

Planting rate = Target population (plants/ha) x 100 x 100
                       No. of seeds/kg x expected field establishment (%) x
                       germination (%)

No of seeds/kg = 28,000 (depending on variety, marked on bag)
Germination % = marked on bag
Expected field establishment (depending on insects, seedbed, machinery):

Precision planter 70-80%
Airseeder (press wheels) 50-70%
Airseeder (no press wheels) 40-60%

Example: 
For a target population of 50,000 plants/ha using a variety with 28,000 seeds/kg, field establishment of 60% and a germination of 95% the rate is:

Planting rate = 50,000 x 100 x 100 = 3.1 kg
                          28,000 x 60 x 95

Approximate number seeds/kg

26,000 to 30,000 (refer to bag label for an exact count).

Germination %

Average 90%. Minimum prescribed 80%. Refer to bag label for the exact figure.

A guide to field establishment percentage
Planter type Establishment range

Precision planter

60-75%

Airseeder/combine with press wheels

50-60%

Airseeder/combine without press wheels

35-55%

Row spacing

  • 25 cm optimum for yields exceeding 4 t/ha.
  • 50 cm for expected yields of 3-4 t/ha.
  • 75 cm for expected yields of 1-3 t/ha.

Under good growing conditions, narrow rows out-yield wide rows. This advantage decreases as soil moisture reserves decline. There may be situations where it is necessary to row crop even though expected yield indicates narrow rows are superior (e.g. where inter-row cultivation is used for weed control).

In dry areas where yields are less than 1.0 t/ha, the row spacing may be as wide as 2 m.

Depending on the planter, twin rows spaced 18-45 cm apart with wide centre give a less cramped spatial arrangement of seedlings and have regularly shown yield benefits.

Seed placement depth

50-75 mm into moisture.

It is only necessary to plant seed deep enough to give it moisture to germinate and allow its roots to grow down through moist soil into subsoil moisture, ahead of the drying front.

Seed treatment to saften seed against crop herbicides

Herbicides containing the active ingredient metolachlor (viz, Dual, Dual Gold, Primextra and Primextra Gold) can seriously damage sorghum plants. When there is need to use these herbicides for in-crop weed control, it is necessary to saften the sorghum seed by pre-plant seed treatment with the seed-saftener, Concep II. Check labels on all seed treatment products for recommended treatment sequences and procedures.

Suitability for zero tillage

Sorghum is the most widely grown zero tillage summer crop in the Burnett. It tolerates compacted subsoil and can stand high presswheel pressure at planting. Good grass control in the crop is essential to achieve high yields but this can be expensive with herbicides. Some farmers are now using shielded sprayers and knock down herbicides prior to planting. The longer the paddock is under zero tillage the easier it is to establish the following crops.

Last updated 28 November 2011