Producers urged to graze 'safe' with dual purpose crops
Author: Toni Somes | Date: 25 Jun 2019
Producers looking to maximise their returns from this season’s dual purpose crops are being urged to adhere to 'safe' grazing principles to avoid damaging the recovery and grain yield of plants.
Research has shown that the 'safe' grazing period extends from when the crop is well anchored, until the reproductive parts start to elongate above the ground and can be damaged or removed by the livestock - DC30 for cereals and bud elongation for canola.
CSIRO Agriculture research scientist Dr Susie Sprague said any crop could be grazed within this window, with the grazing delaying flowering by between two days and two weeks depending on grazing duration.
“Our studies have demonstrated that time of lock-up and residual biomass are the critical issues when it comes to decision making but, of course, ultimately decisions will depend on grain verses livestock prices,” Dr Sprague said.
“We can define the overall grazing window into 'safe' (generally mid-May to mid-July), 'sensitive' (generally mid-July to early August) and 'unsafe' (generally early August onwards) periods which are related to the impact on grain yield.
“The 'safe' grazing period is once the crop is well anchored and there is still plenty of time for recovery after a period of grazing, even if the crop is grazed quite heavily.
“The `unsafe’ period is when the reproductive parts of the crop (spikes in wheat, or buds in canola) are elongating above the ground and can be removed by stock, and there is also too little time for the crop to recover enough biomass by anthesis to set a reasonable yield potential.
“Most growers can easily identify these two periods by testing crop anchorage to start grazing and checking crop development stage to stop grazing.”
The intermittent period, the `sensitive’ period, is when the crop has not yet begun to elongate, but where yield recovery can be very sensitive to the amount of residual biomass left.
“This is the period where some idea of how much residual biomass is needed to reach a specified target grain yield can assist growers with lock-up decisions to avoid yield loss while maximising grazing potential,” Dr Sprague said.
Grazing strategies for dual purpose crops were a discussion topic at the Grains Research and Development Corporation (GRDC) Grains Research Updates earlier this year and a paper detailing the yield and gross margin impact of different grazing periods and strategies can be found on the GRDC website www.grdc.com.au or by clicking here:
Over the years the CSIRO and the GRDC have partnered in a number of research projects aimed at assessing the grazing potential, recovery and gross margin returns of a range of dual purpose crops.
The research has demonstrated that with good management, the period of grazing can increase net crop returns by up to $600 per hectare and have a range of system benefits including widening sowing windows, reducing crop height, filling critical feed gaps, spelling pastures and providing flexible exit options in dry years.
At the main trial site near Greenethorpe, experiments have assessed different times and intensity of grazing to investigate the relationship between residual biomass (lock-up), critical biomass (anthesis) and target yield.
In one example, a typical grazing Kittyhawk wheat crop sown on April 10 with a target yield of 4.5 tonnes per hectare would require a critical anthesis biomass of around 8-9 t/ha.
This critical biomass would require at least 0.5 t/ha of residual biomass to be left in late July when the crop becomes unsafe to graze without removing elongating heads - i.e. heads removed if past Z30.
“Grazing past this point would require close attention to grazing height to ensure heads were not being removed, and more residual biomass (1 -1.5 t/ha) would be needed to be left at lock-up in mid-August to achieve the same critical anthesis biomass, because there is less time left to reach the biomass for the target yield,” Dr Sprague said.
“For canola the residual biomass requirement left after grazing is higher than wheat, due to the inherently heavy and thick stem bases and slower regrowth after grazing.
“Spring canola requires about 1.5 t/ha of residual biomass left when locked up at the end of July (when the stems begin to elongate) to ensure 2.5 to 3.0 t/ha yield potential.
“Earlier-sown winter canola has even thicker stem bases and requires around 2.5 t/ha of residual biomass for recovery.”
For more information, download the GRDC Dual purpose crops Factsheet from the GRDC website www.grdc.com.au or click here:
Dr Susie Sprague, CSIRO Agriculture research scientist
Toni Somes, GRDC
0436 622 645
GRDC Project code: CSP00160, CSP00132, CFF00111
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