Sheep take sting out of frost
GroundCover™ Issue: 122 | Author: Melissa Williams
Running more sheep and using crop grazing in early winter have become key tactics to manage frost risk on the Bencubbin property of Nick and Tryphena Gillett.
Although the pair has escaped the scourge of frost in recent years, a run of extreme incidences in the early 2000s means this issue remains central to their long-term risk-management planning.
Nick says their 9000-hectare property was severely affected by frost in 1998, 2001, 2002 and 2005.
He estimates the 1998 frost completely wiped out yields from 20 per cent of wheat plantings and in 2005 about 40 per cent of the total wheat program was lost.
In 2005, T-TEC temperature loggers were placed at crop canopy height on the Gillett property, based on Nick’s research that found these data recorders were accurate and commonly used in the Australian refrigeration and transport sectors.
That season the loggers showed three frost events, with durations of six to seven hours below –2°C between August and mid-October (the final event was highly unseasonal).
Nick says in that period there were almost weekly frosts of lesser severity, but that caused production losses of up to one tonne/ha in each cereal variety at each time of sowing.
“After that year we decided to stop pushing so hard on continuous cereal rotations and allocated more frost-prone land to pasture and running sheep to spread risk in the cropping operation,” he says.
“We identified frost-prone areas using several years of yield maps, coupled with our local knowledge and experience.”
During the past five years, the Gilletts have pushed stocking rates higher and now run an 800-head breeding flock of Dorper ewes on pastures that make up about 10 per cent of arable farm area.
The sheep are used for strategic crop grazing to help optimise livestock enterprise productivity and mitigate frost risks by delaying flowering dates for wheat crops. Wheat crops are grazed in the early vegetative stage in years when sheep feed is in short supply.
To date, barley crops have not been grazed on the property as Nick says they are less susceptible to frost damage. But he has not ruled this out if needed in future.
The Gilletts grow Mace and Calingiri wheat and Hindmarsh, Scope and Litmus barley.
They use both wheat varieties for early-season grazing if required and have not witnessed sheep having a preference for either.
Nick says variety choice and time of sowing are not especially difficult decisions for crops earmarked for sheep grazing in his area because grazing can slow advancement of crops if they are getting away too fast.
“But knowing we can graze our cereals without suffering a yield penalty means we can use early-sowing opportunities to get a crop in the ground and established if we get really early rain – and then slow its development down by about one week for every two weeks grazed with the sheep,” he says.
Nick says in 2015 good summer and autumn rain meant his pastures got away well and there was no need to graze cereal crops because sheep feed was adequate.
He says in years when wheat crops are grazed, sheep are only put into paddocks sown before 10 May and are introduced at the two-to-three-leaf stage (GS13).
All classes of sheep (except lambing ewes) are used for crop grazing on the property and stocking rates can be as high as 10 dry sheep equivalents/ha.
Grazing periods depend on time of sowing, and Nick works on the Department of Agriculture and Food, Western Australia (DAFWA) recommendation that if he wants to extend flowering by one week, he will graze crops for two weeks.
All sheep are removed from crops before they reach DAFWA’s recommended GS30 to GS31 (the start of stem elongation).
“In my experience of crop grazing, you can never have too many sheep on the crop and the faster the crop is crash-grazed, the better,” Nick says.
“Grazed crops do require more nitrogen and I use a post-grazing application of 10 kilograms of nitrogen/ha for crop recovery.”
Nick is a member of the GRDC’s Regional Cropping Solutions Network Kwinana East group, which has identified frost risk management as a research priority for this port zone. He says frost is a complex constraint to deal with in his farming system and recognises that a comprehensive risk-management plan is required.
The GRDC has long recognised the significant challenge of frost mitigation for Australian growers and is addressing this through its multidisciplinary National Frost Initiative (NFI).
Through the NFI, the GRDC is now producing frost susceptibility rankings for most commercial wheats used in WA to help growers compare varieties.
This data is based on three years of national research into field-based frost damage, including at trial sites near Wickepin and Merredin, and is available at the National Variety Trials website.
0427 862 007,
Dr Juan Juttner, GRDC general manager, genetic technologies,
02 6166 4500,
Julianne Hill, RCSN,
0447 261 607,
Ground Cover Supplement – frost
GRDC Project Code UA00136, CSP00180, YOU00002, CSP00143, DAW00234, DAW00241, UMU0045, CMA00002, UQ00071, CSE00198, CLT00001