Paddock Practices: Key considerations for grazing crops in WA

Key points

• Early sowing and grazing critical to dual-purpose crop success
• Grazing crops decreased yields in most trials
• Livestock gross margins generally increased from grazing winter crops
• Grazing crops lightly and early in the growing season results in smaller yield reductions
• There are several keys to improving whole farm profit through crop grazing

Growers opting to graze crops in order to fill the winter feed gap are reminded to monitor such crops closely to avoid any yield penalties which might result from grazing.

Grazing crops has increased in prominence in WA over the last decade, with mixed farmers using it as a tool to improve livestock productivity and whole farm profitability.

Research conducted in WA over a seven-year period between 2000 and 2017 showed grazing crops can offer significant benefits to livestock through superior feed quality.

However, according to agVivo consultant Phil Barrett-Lennard, grazing reduced crop yield in most cases.

“Occasionally yield is improved by grazing and when this occurs, it is often where a delay in flowering has helped the crop avoid a frost event,” he says.

“The size of any reduction in crop yield is largely governed by the timing and intensity of grazing, but also by the interaction between grazing and other environmental stresses such as heat, moisture stress or waterlogging.

“Research in WA shows a very clear trend where the earlier and lighter a crop is grazed, the lower the negative impact on crop yield.”

When crop grazing is managed appropriately, Mr Barrett-Lennard says yield reductions in the 0 to 10 per cent range should be expected.

“To improve whole farm profit, the aim is to more than offset the lost income from these small yield reductions with an increase in profitability of the livestock enterprise,” he says.

Early sowing and grazing

A critical component in the success of grazing winter crops and minimising yield loss is early sowing and grazing.

Mr Barrett-Lennard says sowing crops destined for grazing early has a huge impact on the amount of biomass available for grazing in late autumn and early winter.

“In Grain & Graze trials at Wickepin in 2014 and 2016, wheat, barley and oats sown in mid-late April produced significantly more early winter biomass than late-May sown crops,” he says.

“Late-May sown crops only produced 50 to 200 kilograms per hectare of edible biomass by early to mid-July, while April sown crops produced 400 to 2200kg/ha of edible biomass by early-mid July, with approximately 50 per cent of that being available by early June.”

He says other research has shown grazing crops lightly – or “clip” grazing the top of the plant – and early in the growing season results in far smaller yield reductions than heavier and later grazing.

“Research and grower observations tell us that crash grazing down to ground level is not recommended,” he says.

Modelling of grazing winter crops at Esperance showed that grazing early sown crops meant canola and wheat yields were the same as or lower than if crops were sown normally and not grazed.

Crop gross margins decreased 38 per cent of the time at an average of $12.91 per hectare, while livestock gross margins increased 100 per cent of the time at an average of $140/ha for a mixture of single and twin-bearing ewes and $287/ha for twin-bearing ewes only.

Trade steer gross margins increased by $87/ha when grazing early sown crops.

The GRDC’s Grazing Cropped Land booklet provides a number of regional considerations for grazing winter crops in WA (figure 1).

Figure 1: Regional considerations for grazing crops in WA.

Rules of thumb

Research conducted in Australia’s southern cropping region by CSIRO has resulted in the development of safe, sensitive and unsafe grazing windows (figure 2) and some rules of thumb.

The early and ‘safe’ grazing period is once the crop is well anchored and there is still plenty of time to recover after a period of grazing, even if the crop is grazed heavily.

The late and ‘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.

At this stage, there is too little time for the crop to recover enough biomass by anthesis (flowering) 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 ‘sensitive’ period is the time when the crop has not yet begun to elongate, but where yield recovery can be sensitive to the amount of residual biomass left. This is the period where an estimate 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.

The general ‘rule of thumb’ established through CSIRO research specifies 1.5 tonnes/ha of dry matter in spring canola and more than 2.5 to 3t/ha of dry matter for winter canola at stem elongation for a 2.5 to 3.5t/ha grain yield. The results also suggest that leaving more than 0.5t/ha residual biomass at stem elongation (growth stage 30) for spring and winter wheat is sufficient to achieve 4 to 5t/ha grain yield.

Growers can follow these rules of thumb to minimise the effect of grazing on grain yields. However, the comparative value of livestock and grain will dictate the management of grazing crops for a particular farm enterprise.

Figure 2: Yield recovery (percentage of ungrazed crop) of grazed dual-purpose crops highlighting the 'safe', 'sensitive' and 'unsafe' periods of grazing. Yield recovery from grazing during the 'sensitive' period for a given target yield is affected by the residual biomass at lock-up. Late grazing reduces the time for recovery, so more residual biomass is needed.

Whole farm profit

Mr Barrett-Lennard says the keys to improving whole farm profit through crop grazing are to run a higher livestock stocking rate, sow crops early to provide crop biomass for grazing in late autumn and early winter when pasture is scarce, minimise grain yield penalties from overgrazing and to graze crops with an economically responsive class of livestock, such as twin bearing ewes.

“If these farming system changes are not implemented along with crop grazing, whole farm profit is likely to remain unchanged or even decline, as too much crop income is sacrificed in the chase for additional livestock income,” he says.

More information

Phil Barrett-Lennard, 0429 977 042, pbl@agvivo.com.au

Other useful resources

• Grain and Graze website