While far too late for this summer's consideration, sowing grain sorghum earlier than previously considered desirable is an option worth serious consideration.
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Detailed sowing time research conducted in northern NSW and Queensland over several years supports sowing earlier than previous recommendations.
The research was initiated as a collaboration between UQ, NSW DPI and QDAFF and has been led by NSW DPI research agronomist Loretta Serafin in NSW with funding from GRDC.
While sowing of grain sorghum is normally advocated when soil temperature reaches 16 to 18 degrees (8am EDST), sowing as low as 12 degrees can be successful, with care, and with yields generally at least as good.
Earlier sowing aims to minimise the risk of flowering and seed set in extreme heat conditions.
Loretta Serafin stresses that avoiding the risk of flowering in heatwaves can never be totally avoided, but earlier sowing, if feasible, lowers such risks.
Under cool soils at sowing (12 degrees) the study notes emergence takes two to three weeks compared to a more normal five to seven days.
Typically early sown sorghum takes more days to reach flowering (longer vegetative time) but flowers at an earlier date than for 16 degrees sowing.
For example, for a given hybrid at Breeza (Liverpool plains), early sown sorghum reaches 50 per cent flowering in around 90 days versus 81 days for 16 degrees sowing.
Given the much earlier sowing time, this shifts the average flowering time forward by two to three weeks than when waiting to sow at 16 degrees.
Grain yield over the three years of research, from Breeza to Emerald in central Queensland, ranged from 1.0 to 12 tonnes per hectare under dryland and irrigation conditions.
Across all these environments and seasons, the yield of early planted sorghum was similar to or higher than later planting dates.
Also, early sowing commonly allows for earlier harvest and therefore improves the probability of being able to resow to a winter crop with at least reasonable subsoil moisture levels.
Loretta Serafin notes sowing earlier than "best practice" is not for every situation and has some provisos.
It is important to monitor soil temperatures and not sow if forecasts indicate soil temperature is likely to fall below 12 degrees for seven days following sowing.
Some forecasters predict temperatures 14 days out with reasonable accuracy.
Because germination conditions are more sub-optimal with early sowing, the researchers stress the importance of high-quality seed, both from a germination and vigour perspective.
Larger seeds generally correlate with greater vigour.
The research has not shown any variety superiority for early sowing options.
As for all sorghum sowings, good levels of stored soil water help guarantee reliable yields.
Sufficient seedbed moisture is also especially important for early sowing to facilitate germination and establishment over the two weeks post-sowing.
Ms Serafin advises considering slightly increasing sowing rates because often establishment from sowing into cooler soils is lower, especially in seasons when the seedbed is drying out.
Accurate seed placement into moisture at three to four centimetres depth, firmed via press wheels, and when aiming for 3.5t/ha or higher solid row configuration with rows 50 to 100cm wide, the advocated sowing rate is to target 50,000 plants established per hectare.
Paddocks with low weed burdens are advocated by Lorreta Serafin and colleagues for early sorghum sowing.
Late winter weeds, as well as summer weeds, combine to present a challenge to early-sown sorghum.
Pre-emergence herbicides, as well as post-sowing pre-emergent options and early post-emergent options, are available.
A further suggestion from the researchers is to sow at least two high-yielding hybrids to spread production risk.
From recent and ongoing GRDC-funded grain sorghum variety trials, each of the companies developing and marketing grain sorghum in Australia have a good range of high-yielding well-performing varieties.
For further details, see the GRDC or NSW DPI website.
Next week: New herbicide for greatly reducing drift risk.
- Bob Freebairn is an agricultural consultant based at Coonabarabran. Email robert.freebairn@bigpond.com or contact 0428 752 149.
