Summer options forage sorghums vs. millet

Tim Burley, AusWest Seeds, North West NSW

Many areas of New South Wales are heading into spring having experienced a lower than average winter rainfall. In many cases winter crops are experiencing moisture stress and with pastures depleted, many growers will be looking for quick feed options in the event of some good spring rainfall.

Let’s take a moment to consider the agronomic factors affecting summer grazing options as well as the pros and cons of using either forage sorghum or millet in your farming system.

Which crop and what variety?

Your choice of crop will depend on a number of factors, these will include varietal characteristics, agronomic factors, end use, available soil moisture and likely in crop rainfall.
FedEx_Sept17 | AusWest & Stephen Pasture Seeds
Feedex being cut for hay at Bundarra, NSW

Forage millets
Millets generally produce less dry matter than forage sorghums but have higher quality feed, particularly for smaller animals such as sheep. Millets also present a better fattening and hay/silage option than forage sorghum. They can be more difficult to establish than the larger seeded sorghums and can be grazed 5 to 7 weeks after sowing but do not tolerate harsh grazing.
There is no prussic acid poisoning risk, but there is a photosensitisation risk with millets. Paddock selection is important, beware of residual herbicides. There are also few herbicides available for in crop weed control. Millet can run rapidly to head in hotter weather so grazing management is important. It is also frost sensitive.

Japanese Millet

  • Shirohie (selection from Japanese) gives better regrowth and is later to mature
  • High quality fodder
  • Graze when 20 – 30 cm high
  • Suitable for sheep
  • Establishs quickly and early growth is rapid
  • Does not tolerate harsh grazing

Pearl Millet

  • Similar production to forage sorghum
  • Recovers well from grazing
  • More drought tolerant than Japanese millet

Pennisetum Millets

  • Good drought tolerance
  • Slow to mature
  • Graze when 40 – 60 cm high
  • Don’t graze below 15 cm or regrowth can be affected
  • Quality reduced when growth exceeds 100 cm

In conclusion, summer forage crops of forage sorghum or millet offer quick and high levels of dry matter production, however careful attention to nutrition and available soil moisture is key to quality production and will drive your choice of crop. Generally speaking if soil moisture is limited or summer rainfall unreliable, then millet is a safer option for a lower risk of stock poisoning and higher quality feed from less moisture. However if starting soil moisture and nutrients is less limiting and in crop rainfall favourable further options for higher dry matter production and prolonged grazing options are available by using forage sorghums.

For further information about varieties available, sowing rates and varieties suitable to your enterprise contact your local territory manager.

Soil nutrition and fertiliser use
Second only to soil moisture, poor plant nutrition is one of the most common reasons for poor forage crop performance. Nitrogen deficiency is the most common deficiency in many soils.
Both forage sorghum and millet crops have a high requirement for nitrogen, particularly if the seasonal conditions are favourable. Top dressing between grazings or hay cuts is often required to sustain optimum growing conditions. Other key nutrients include phosphorus, sulphur and potassium.
Nutrient removal from the soil can be very high, for example, a dryland crop of forage sorghum yielding 10 tonne per hectare of dry matter will remove the practical equivalent of the below fertiliser per hectare:

  • 550-600 kg Urea
  • 350 kg single super
  • 400kg muriate of potash

Crop rotation factors
The paddock must be selected ensuring that there are no residual chemicals in the soil. This can be exacerbated by drier conditions with a lack of rainfall maintaining residuals in the soil which can affect plant establishment. For example, any Metsulfuron used in a fallow period, or the use of atrazine and/or metalochlor must be considered in the rotational choice for the next crop.

Unless irrigation is available most situations will require a fallow to have adequate starting soil moisture for a summer forage crop, particularly in areas were summer rainfall is unreliable.

Forage sorghum
Forage sorghum is the most productive and fastest growing forage. It can produce large volumes of feed relatively quickly. As a general rule, forage sorghum can be sown when the frost risk has passed and soil temperatures have reached at least 16°C at the intended sowing depth at 9am in the morning.

Forage sorghum can be grazed once the crop has established secondary roots, reaches 50 cm in height and is unstressed. If the crop is stressed, there is a high risk of prussic acid and /or nitrate poisoning. Forage sorghum will generally reach grazing height eight weeks after sowing. Several cuts or grazings are possible in good conditions.

Hybrid Forage Sorghum (Sorghum x Sudan grass hybrid)
Available varieties: Feedex, BMR Fuel

  • Stem of medium thickness
  • Grazing in 7 to 8 weeks
  • Graze when >50 cm, but check variety
  • Prussic acid risk

Sudan Grasses (Sudan grass x Sudan grass hybrid)
Available variety: NuDan 

  •  Less feed than forage sorghums
  • Stems are very fine
  • Quicker initial growth

Lower prussic acid risk

Sweet Sorghums (Sweet sorghum x Sweet sorghum)

  • Retain feed value and palatability
  • Stem relatively thick
  • Higher levels of prussic acid than the forage sorghums during early growth
  • Graze when 150 cm high
  • Regrowth after grazing is inferior

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