Planting in Northern New South Wales and the Darling Downs has traditionally commenced from early October.  Planting in the Downs and western areas of Northern NSW is normally in  early October, with the eastern areas favouring late October. 

In the past, plantings in late September have had successful establishment however field variation and paddock selection is extremely important with these early plantings.  Lighter soils with a north-easterly aspect will warm up more quickly and be more conducive to successful seedling establishment than a heavy clay soil on a southern slope.

The key to reliable sorghum crop establishment is adequate seedbed or soil temperature along with sufficient but not excessive soil moisture.  The recommended minimum soil temperature for adequate germination and establishment is 16 to 17°C taken at 9am.  This temperature should be taken at planting depth and should be taken over a number of days prior to planting to ensure that the temperature is rising.

Low soil temperature slows the germination process.  At 17°C seedlings will take seven to 10 days to emerge.  However, at 15°C seedling emergence time will extend out to 11 to 14 days.  The longer it takes a seedling to emerge, the greater the risk of that seedling being attacked by soil borne insects or diseases.

The following table highlights the effect of soil temperature on seedling emergence.

This table demonstrates the fact that sorghum will germinate at relatively low temperatures but satisfactory emergence won’t occur until temperatures are higher. The relationship between soil temperature and soil moisture is also extremely important for seedling establishment.  Cold wet soils are ideal for soil borne diseases to attack the slow growing seedlings.  

Summary

• Three to four days prior to planting, take soil temperature readings at 9am at planting depth
• Ensure that soil temperature is at least 16 to 17°C and rising
• Ensure that adequate soil moisture is available
• Slower emergence will result in higher seedling mortality
• If rain falls after planting and before emergence, the temperature generally drops and the incidence of soil borne diseases will be much greater.
• Planting is best delayed until adequate seedbed temperature has been achieved.  Generally, early plantings mature at the same time as planting two to three weeks later when the seedbed has warmed up.