Mallee farms get help to better identify frost

Attendees were given updates on the latest National Frost Initiative research from across the country, SARDI’s Peter Hayman and CSIRO’s Uday Nidumulo outlined frost mapping and predicting frosts, while Agrilink consultants Mick Faulkner and Jeff Braun gave an update on some of their local on-the-ground experience. 

Mr Braun said identifying frost events was not as simple as seeing ice the next morning on the back lawn.

“In some frost events ice can form during the night and can melt before morning,” he said. 

“It certainly happened in the Mid North last year as there were some devastating frosts that affected yields but many people didn’t realise that they had happened.

“People need to know when they’ve had a frost event in order to identify if they have had damage and plan a course of action.” 

Farmers were advised to wait up to a week before assessing damage as symptoms are difficult to pick the day after the event andoften became more readily visible closer to a week after the event.

“It can still be timely a week after a damaging frost event to either cut the crop for hay or graze it out,” Mr Braun said.

Mr Faulkner also advised attendees, if unsure of a frost event, to mark a few heads with coloured ribbon so that grain development could be easily monitored.  

The other option was to soak the base of a plant with water/food dye mix and monitor where the dye accumulates in the tissue.  Frosted tissue will not accumulate dye. 

Investing in weather sensors, such as Tinytags, was also advised for more accurate frost determinations.

“There can be a substantial difference between the Bureau of Meteorology’s reporting method, which is 1.2 metres above the ground versus head height in the canopy,” Mr Braun said.

“We have measured up to 2 degrees Celcius lower temperature at head height than at 1.2m above the ground.”

Users would need to keep the temperature sensors just above the crop for best frost determination and as such, would need to be adjusted as the crop grew.

Other management tips included sowing crops into reduced residue loads as often thick residues could worsen the effects of frost.

“High stubble loads can prevent the soil from warming up and during the day, so at night the soil can’t release this heat back to atmosphere to buffer against the cold air descending onto the crop,” Mr Braun said.

Farmers could also consider growing a mix of wheat varieties with different developmental triggers to reduce risk.

“There was some very early-sown (March 17th) Scepter wheat in a local SARDI time of sowing trial which showed heavy frost damage to the grain whereas in plain view it appeared to look very good, but when you threshed out some of the heads the grain was undeliverable,” Mr Braun said.

“The trial highlighted that people should utilise a range of developmental triggers in varieties and avoid having their whole farm sown to varieties on that were temperature driven and all developed very quickly.

“It may pay in frost prone areas to have some varieties with photoperiod/vernalisation development triggers and possibly even have them as a mix, so unless you have an absolutely catastrophic frost event, you are likely to always get something back.

“Past frost trials looking at varietal mixes haven’t always been conclusive, but we have seen from in-paddock experience in the Mid North and Mallee that it can work in helping to lessen the impact of frost events.

“People considering mixing varieties should try to utilise varieties of similar quality classification, such as three APW varieties or deliver to the lowest varietal classification in the mix.”

Mr Braun had a client utilising a mix of three varieties with different developmental rates in a frost-prone environment. 

“It was three varieties they were already sowing separately, and instead of throwing wheat out as an option entirely due to frost risk, it was decided to put them all together in a mix to gauge how it went,” he said.

“It is only a broadacre management proof of concept, and not a trial per se, but it will help us see how it performs in this environment and whether it is a viable option moving forward. At this stage the results look promising.”

Otherwise Mr Braun suggested farmers in frost prone areas should consider not growing wheat at all.

“If you are regularly getting frosted in certain areas, sometimes the most logical action is to grow a crop that is less frost-sensitive at certain times of development, such as oats, barley or hay, or have more pasture and livestock,” he said. 

“They can still get hammered by frost depending on the timing, but based on paddock experience they’re certainly less prone than wheat.

“People also have to bear in mind that if a frost event is early enough in the season, such as early to mid-August, and there is sufficient soil moisture and nutrition, re-tillering can occur and the crop may recover to a large degree.

“But the later it happens, the less time you have for these tillers to produce viable grain, particularly with moisture stress coming in later in the season.” 

If farmers are growing pulses or oilseeds, Mr Braun said the break crop trials observed during the field day showed that some crops, such as lentils and beans, could potentially protect some of their pods within their canopies or in the case of chickpeas which are more indeterminate in their flowering and could possibly re-flower and fill pods after a frost event providing soil moisture is adequate. 

Both these crops are a better option than crops, such as peas, which were extremely sensitive to frost and don’t tend to flower a great dealafter the early pods have been frosted.

”It doesn’t make the other crops frost-proof, but often you can still get part of a crop, whereas with peas possibly not,” he said.

When it comes to cutting frosted crops for hay, Mr Braun said sometimes it wasn’t always a profitable option as “last minute” cutting can have poor yields and quality due to inadequate preparation.

“On frost-prone areas of their farms, farmers should have the paddock prepared for hay cutting just in case by levelling the surface after sowing by chaining, rolling or both; don’t leave it to the last minute as it can be detrimental to yields and quality,” he said. 

“This occurs when the hay cutter can’t cut as low as it needs to on rough surfaces, hay will often fall to soil surface with wide row spacings if cutting direction is the same as sowing direction and pre-existing cereal stubble can be raked into the hay windrow reducing quality. 

“Cutting crops for hay in the Mallee can be more daunting to start with because of the area involved – very few farmers want to go out and cut thousands of hectares of hay if they can avoid it.

“Frosts can also be quite patchy in nature so cutting large areas isn’t always the easiest option.”

Applying nutrients to the crop to prevent frost damage is not the “silver bullet” people want it to be either. 

“Certainly where there is known pre-existing copper and/or potassium deficiencies, applying these nutrients to the crop would helplessen the severity of frost damage,” he said.  

“But in the Mallee, deficiencies of Copper and Potassium are fairly rare, except maybe on some white sands, clay spread sands or badly eroded sand hills. 

“Outside of these situations where a deficiency has been diagnosed there is very little the application of these nutrients will do to prevent frost damage to your crop.”