Grains Research and Development

Date: 08.04.2014

Stubble removal can help reduce frost risk in prone areas

Author: Melissa Williams

Key points:

  • Standing stubble biomass of more than 2.5t/ha can increase spring frost severity by up to 0.6°C in low-lying areas.
  • This stubble load can also prolong frost duration.
  • Reducing stubble loads to 2t/ha can lift yields by 0.6-0.8t/ha if frost hits during the flowering window or early grain fill.
  • Determining optimal stubble loads to reduce frost risk will be a focus of 2014 western region research.

Research in WA’s central and southern wheatbelt indicates removing or lowering stubble loads to about two tonnes per hectare using burning or raking can boost wheat yields by 0.6-0.8t/ha in frost-prone, low-lying areas.

A stubble load of 2t/ha equates to about 70 per cent ground cover.

Trials initiated by the GRDC’s Albany and Kwinana East Regional Cropping Solutions Networks (RCSNs) in 2013 found no or low stubble levels reduce the severity and duration of spring frosts and lift crop yields, compared to retaining high stubble loads in frost-prone areas.

The trials, led by the Department of Agriculture and Food WA’s (DAFWA) Dr Ben Biddulph and run in conjunction with Living Farm and Facey Group, were set up at York, Wickepin and Nyabing.

These will be repeated again this year, with GRDC funding, to further investigate the effect of stubble amount and orientation on frost severity, frost duration and crop yields.

Living Farm project coordinator Rebecca Jenkinson told the recent Agribusiness Crop Updates that preliminary trials run by the Living Farm Group in York in 2012 showed plots where stubble was burned:

  • Were 1°C warmer at canopy height than retained stubble plots during a frost event
  • Spent an average of one hour less below 0°C during a frost
  • Produced an average wheat yield of 1.7t/ha compared to retained stubble plots at 0.4t/ha.

This reflected findings of a Facey Group trial in 2012, where wheat yields were 0.7t/ha higher in burnt stubble plots high in the landscape (with moderate frost risk) and 0.3t/ha higher in burnt stubble plots lower in the landscape (with high frost risk), compared to retained stubble plots.

What is the stubble effect?

Stubble appears to insulate the soil surface, lowering the amount of heat absorbed into the soil during the day compared to areas with no stubble.

It is also thought that less heat is radiated from the soil at night on areas where stubble is retained. This lowers the canopy temperature and increases frost damage.

Severity and duration of frost - 2013 trial results

Temperature loggers placed at the top, middle and low parts of the slope at the York, Wickepin and Nyabing trial sites in 2013 recorded significantly colder minimum canopy temperatures in plots with high stubble loads.

At the Living Farm York site, there were 12 frost events - where hourly canopy temperature was below 0°C.

The average minimum temperature in removed stubble plots during these frosts was -0.6°C, which was 0.5°C higher than the average in the standing stubble plots.

The frosts at York did not coincide with flowering, so wheat yields were unaffected.

At the Facey Group’s Wickepin site, there were nine frost events – but these did not coincide with the flowering window either.

During these frosts at Wickepin, the removed stubble plots had average minimum canopy temperatures of -0.5°C, compared to -0.7°C in retained stubble plots. 

At the Nyabing trial site, sown with Yitpi on May 31 into canola stubble, there were six frosts in September – prior to and during flowering – and another nine after flowering during grain development in October.

Frost impact was most severe in plots with high stubble load (3.5t/ha) that were low in the landscape, where minimum temperatures were 0.4-0.6°C colder (and averaged -2.4°C) and lasted longer than in standing stubble (2.5t/ha) and removed stubble plots (0.5t/ha) respectively.

Wheat in high stubble plots at this site appeared to have up to 65 per cent more frost-induced sterility (number of flowers aborted) than removed stubble plots.

The high stubble load plots low in the landscape at Nyabing produced wheat yields of 0.6t/ha, compared to an average of 1t/ha for all standing stubble plots at this site and an average 1.8t/ha for all removed stubble plots.

Screenings at harvest were also high, at about 60 per cent, where stubble loads were high. Screenings from the other treatments were about 9 per cent.

On-farm implications

Results from the grower group trials in 2012 and the 2013 GRDC RCSN-DAFWA stubble trials indicate reducing stubble load in frost-prone, low-lying areas can potentially lessen economic losses from frosts that coincide with the cereal flowering window.

Dr Biddulph says for growers considering burning or raking heavy stubble residues from 2013 crops, it is too early to provide definitive thresholds for optimum stubble levels.

But research will continue across southern WA to further assess stubble load parameters for a range of regions, seasons and seeding systems.

It is recommended growers do not remove all stubble across properties, but concentrate on low-lying frost-prone areas.

The benefits of this strategy include:

  • Increased canopy temperature during frost events
  • Less time that canopy temperature falls below 0°C
  • Less risk from yield loss.
  • Cost-effective frost risk mitigation.

Stubble research efforts in 2014 and beyond

GRDC-funded trials in 2014 will investigate the orientation and height effect of stubble – standing or horizontal – and the interactions between soil type, stubble and frost.

As part of the GRDC’s increased investment into frost research - at $3 million nationally per year from 2014 to 2019 - DAFWA will also this year be conducting research into:

  • Stubble architecture
  • Crop row orientation
  • Stubble composition and colour
  • Wider crop row spacings.

This research complements GRDC and DAFWA’s ongoing efforts to advance the genetic tolerance of cereals to frost and management strategies to reduce risks.

Top 10 pre-seeding tips to minimise frost risk in WA

GRDC ran a series of Pre-Seeding Frost Workshops across WA during March, bringing together leading researchers from DAFWA, CSIRO, ConsultAg and Living Farm.

During the workshops, ConsultAg director Garren Knell outlined the top pre-seeding strategies for WA growers to consider during autumn to minimise crop losses from spring frosts. These are outlined below:

Action

Description

Strategy

Asses frost risk

Growers should identify and map high frost risk paddocks using previous experience, landscape position and soil type.  High risk paddocks should be farmed differently to reduce the financial exposure and severity of loss in a frost year.

Planning

Remove stubble

Retaining heavy stubble burdens (more than 2.5t/ha) can increase risk of frost damage, making the frosts colder and longer with lower temperatures at head height.  The stubble is reducing heat radiating from soil at night, resulting in less warming of the canopy.  Retaining stubble (especially canola) can make cutting hay unviable in the advent of a severe frost event. 

0.5-1oC

Reduce inputs

Don’t use the high input package on frost-prone paddocks. High input crops on frost-prone areas are frequently more severely frosted than lower input crops with a lower target yield. Reducing N, P and seed rates reduces risk and returns  competitive - if not better – gross margins, even if there are only minor frost events.

Tolerance

Crop selection

Pasture rotations are a lower risk. 

Oats are the most frost tolerant crop, at 4°C more tolerant than wheat.

Barley is 2°C more tolerant to frost at flowering.  During grain fill, researchers are unsure if there are any differences in tolerance between wheat and barley. 

Canola tolerates flower frost well, but is regularly severely frosted during grain fill. 

Growing hay on high frost risk paddocks is a good frost avoidance strategy.  However quality hay production is also a risky enterprise.

Tolerance

Spread flowering time

For businesses in frost-prone areas, it is important to ensure that crop variety choice and planting time do not result in all the wheat crop flowering at the same time. The DAFWA model FLOWER POWER is a useful way to compare time of sowing and variety choice, to ensure a wider flowering window to spread the risk of frost and heat stress.  This can be found at: http://grains.agric.wa.gov.au/flower-power

Risk management

Delay sowing

Delaying sowing of wheat to ensure that the crop is flowering at a time when the incidence of frost is lower is a valid frost avoidance strategy.  This is best achieved with later sowing of long season varieties in frost-prone sites.  There is a loss in yield potential of 20kg/ha/day - or 5% per week - that must be traded-off against frost risk.

Avoidance

Blend varieties

Blending two wheat varieties (long and short season) is an effective strategy for balancing frost risk with end of season drought. Multiple frost events that damage both varieties are rarer.  Yitpi and Mace work well together – being AH varieties. 

Avoidance

Crop tolerance

Crops deficient or marginal in K and Cu are likely to be more susceptible to frost damage.  Supplying luxurious levels won’t buy any additional tolerance above adequate supply.

Tolerance

Grazing

Grazing a crop is the only practical way to alter a crop’s flowering time after seeding.  Graze early (at the 4-5 leaf stage) to minimise yield impact.  Fourteen days grazing delays flowering by about seven days.

Avoidance

Cultivation

A range of cultivation options (scarifying, mouldboard ploughing, spading and ploughing) have been observed anecdotally in the field to reduce frost damage.  This is yet to be proven scientifically.  Cultivation may influence the amount of heat held in the soil by ameliorating a non-wetting soil and bringing darker soil to the surface. This will be tested in 2014.

0-1°C

Claying

Claying increases soil heat bank by darkening soil colour and retaining moisture nearer the surface.  However, the cost of claying is prohibitive if claying only for frost minimisation. 

0-1°C

Crop Architecture

Sowing on wide rows offers no frost benefit and results in loss of yield potential.  Narrow row, low seed rate seems effective in tolerating frost.  Research is being conducted into row configuration to alter crop canopies.

Tolerance

 Source: Garren Knell, ConsultAg


ENDS

More information:

Rebecca Jenkinson, Living Farm,
0409684818,
rebeccaj@livingfarm.com.au

Garren Knell, Consult Ag,
08 9881 5551,
gk@consultag.com.au

Ben Biddulph, DAFWA,
08 9368 3431,
ben.biddulph@agric.wa.gov.au

Julianne Hill, RCSN coordinator,
0447261607,
regionalcroppingsolutions@gmail.com

Useful resources

Rebecca Jenkinson’s 2014 Agribusiness Crop Updates paper:
http://www.giwa.org.au/2014-crop-updates

Regional Cropping Solutions Network:
www.grdc.com.au/rcsg

GRDC Ground Cover Frost Supplement, March-April 2014 edition:
www.grdc.com.au/GCS109

GRDC Managing Frost Risk ‘A Guide for Southern Australian Grains’:
www.grdc.com.au

GRDC Fact Sheet:  Managing the Risk of Frost:
www.grdc.com.au/GRDC-FS-FrostRisk

DAFWA Flower Power tool: 
http://grains.agric.wa.gov.au/flower-power

GRDC Project Code KW/Alb12/13-JointProj4; Alb11/122of4; DAW00234; SDI00019

Region West