Down to Earth with Bob Freebairn: Research guide for Sorghum strategies for high yield

NSW DPI research agronomist Loretta Serafin led the NSW arm of the research with extensive trial sites at Breeza in the Liverpool plains, Moree and Mungindi.

Grains Research and Development Corporation (GRDC), The University of Queensland (UQ), NSW Department of Primary Industries (DPI) and Queensland Department of Agriculture and Fisheries (QDAF) funded the research.

NSW DPI research agronomist Loretta Serafin notes that under cool soils at sowing, at 13 degrees, emergence takes up two weeks compared to a more normal five to seven days.

Early sown sorghum takes more days to reach flowering, with a longer vegetative time, but flowers at an earlier date than for 18 degrees sowing.

A given hybrid at Breeza from 13 degrees sowing, for example, would be expected to reach 50 per cent flowering in around 90 days compared to 81 days for 18 degrees sowing.

Even with slower growth from early sowing, average flowering time is around two to three weeks earlier than sowing at 18 degrees.

Based on long term temperature records, earlier sowing significantly lowers heat stress risk at flowering.

Sowing earlier than previously considered "best practice" is not for every situation and has some provisos, Ms Serafin stresses.

It is important to monitor soil temperatures and not sow if forecasts indicate soil temperature is likely to fall below 13 degrees for seven days after sowing. Best available temperature forecasts help avoid high risk of facing a prolonged period of below 13 degrees soil temperatures.

Germination conditions are more sub-optimal with early sowing hence the research supports the importance of high quality seed - both from a germination and vigour perspective.

The research notes some varieties have improved cool soil germination ability with seed companies having data to support their best early sowing lines.

Slightly increasing sowing rates are advocated for 13 degrees sowing as establishment from sowing into cooler soils can at times be a bit lower. Optimum plant density across the trial sites, sowing times and seasons was 60,000 per hectare (six plants per square metre).

Higher yielding situations favoured six to 12 plants/m2 but higher plant populations also require higher seed costs for similar yields.

Plant populations of three plants/m2 were adequate in low yielding situations but reduced yields by 1t/ha at high yields.

Hybrid performance also varies depending on the sites yield potential.

Grain yield over the study period, from Breeza to Emerald, Qld, ranged from 1 to 12t/ha under dryland and irrigation conditions.

Across all these environments and seasons yield of early planted sorghum was similar or higher than later planting.

Early sowing commonly allowed for earlier harvest and therefore improved probability of being able to re-sow a winter crop with reasonable sub soil moisture.

Grain quality, the research noted, can be better from early sowing compared to more traditional sowing time.

Ripening stress is generally less and terminal drought commonly reduced.

There was also less lodging associated with early sowings.

Ms Serafin stresses that for all dryland sorghum sowings, good levels of stored soil water is critical for reliable yields.

Paddocks with low weed burdens are advocated for early sorghum sowing.

From 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 of this study see the publication recently released, "Optimising sorghum production in variable climates", on the NSW DPI web site.

Next week: Coping with CSIRO/BOM predicted climate change.