While January 2006 rains in excess of 100 mm fell in most areas of WA and resulted in plentiful subsoil moisture, the break of season rains expected in May did not eventuate and many growers faced a difficult decision. Do you seed into a dry seedbed covering good subsoil moisture, or wait for breaking season rains?
No-till, and the ability of the system to chase moisture in dry starts proved integral as growers seeding early were able to plant on time and very importantly, germinate a crop using the subsoil moisture.
In 2006, the WA No-Tillage Farmers Association (WANTFA) visited a number of growers who grew good crops despite the drought and attempted to quantify whether using a no-till system was improving their bottom line. Some lessons were identified
Lesson 1: Conserve summer moisture – spray out weeds early
Controlling summer weeds early – through either spraying or grazing means that water is retained in the soil. A good stubble layer, of at least 50 per cent ground cover, will reduce weed germination and protect soil from water losses through evaporation.
Tammin growers, Colin and Libby Huthcinson calculated that having crops germinate on time meant their crops were three to four weeks ahead of those sown under a more conventional planting system. This equating to about an extra one tonne per hectare in yield potential. No-till gives them the flexibility to start seeding early, deep into good subsoil moisture and be less reliant on breaking season rainfall events.
Lesson 2: Improve water use efficiency
The French Schultz (F/S) equation relates grain yield to measured water use and is one way to measure water use efficiency (WEU) in crops. Another rule of thumb is 10 kg grain per mm of growing season rainfall.
Bill Bowden, Department of Agriculture and Food WA (DAFWA), estimates that the F/S equation accurately predicts yields in only the top 95–98 per cent of years (that would have an optimal rainfall distribution to crop requirement).
Following is a quick calculation of water use efficiency at the Hutchinson’s Tammin property.
Site 1 has been continuously no-tilled for 12 years with controlled traffic and full stubble retention.
Site 3 is a leased block that has been sown with no-till principles and had good summer weed control and the third site is a local site (not Colin’s), sown with knife points but with little stubble retention or summer weed control.
The rainfall at each site was considered to be equivalent (129 mm). To calculate estimated soil moisture at the start of the season (May 15), daily rainfall figures were entered into PYCAL (Potential Yield Calculator, 1993) from DAFWA which was calculated to equal 81 mm of rainfall at sowing. Yields were measured at each of the three sites.

The long term no-till, stubble retained and controlled traffic site had three times the WUE of the site with no retained stubble due to the increased moisture infiltration into the soil and it’s ability to retain it. There was also no moisture loss through summer weeds.
Residue cover slows any water running off the paddocks, increasing the time available for infiltration and reducing soil temperature and evaporation.
How can I change a soils water storing capacity?
Increasing rooting depth means that the depth of soil into which plant roots can grow doubles, hence doubling your ‘bucket’ size. Overcoming subsoil constraints such as hard pans, acid layers, water logging at depth and poor soil structure can increase rooting depth.
Adding clay or boosting soil organic matter levels (OC) can improve the water storage capacity in any depth of soil. Increasing OC by one per cent to a depth of 15 cm, equates to 15 tonnes of OC per hectare – meaning this soil can now hold twice its own weight in water (30 tonnes) or has three mm of extra water storage capacity.
Building OC up to a steady state (related to soil texture) is a slow process, but retaining residues (not burning) and reducing tillage so as not to oxidise as much carbon, will help.
Lesson 3: Correct bar setup is so important
A dry topsoil meant seed needed to be placed consistently into the moisture band (about 50 mm) and pressed well to develop good seed/soil contact which is essential for good germination.
Wes and Meg Bakers from Bulyee found areas of very low germination due to some of the seed being placed in the dryer soil and grain malting due to incorrect bar set-up and inadequate break-out pressure.
For tynes, good breakout pressure is vital as a vibrating tyne and attached seeding boot can cause variability in seeding depth between 10–15 mm as the tynes flex backward. Growers with lower breakout could limit this problem by reducing speed as this also reduces trifluralin damage from soil throw at deep working depths.
Another option is to run a coulter in front of the tynes to break up the soil surface. This reduces soil throw as the surface soil flows around the tyne behind the coulter cut, instead of being shattered by compression forces applied by the tillage point.
The success of disc systems in establishing crops was variable depending on machinery setup and design. Ensuring adequate sowing depth to access the sub-soil moisture proved problematic for many growers. One factor affecting seeding efficiency of disc machines was their ability to enter the soil as this is related to machine weight and disc size.
Around the state, growers using single disc machines, placed depth gauge wheels high for additional depth. Growers using double disc modules, which require a large diameter, tended to use a deep set leading coulter.
With correct bar set-up, growers will have the confidence to place seed where it is needed every time.
Lesson 4: When you start, don’t stop!
Many growers in the northern agricultural region in WA continuously stated, ”When we start, we don’t stop. Whenever we have stopped, we always regret it later.”
The reasoning behind this is the effect of sowing date on crop yield and quality.
Late germinating crops (due to either late sowing or late germination) had a larger pre-anthesis water use compared to its post-anthesis use. Pushing flowering date back limits time available for grain fill and can lead to increased screenings.
But there can be good agronomic reasons to stop seeding in dry soil as the furrows produced by tynes are often weak. These can become a risk in a large rain, both from chemical damage and from furrows filling up causing seed to be deeper than the coleoptile length. These were risks many growers took and benefited from.
The Bakers at Bulyee received a total of 417 mm rain, although only 167 mm fell in the growing season. They started seeding in May as usual although they sowed seed deeper at 50 mm (two inches) into the sub-soil moisture.
In 2002 they had seen first hand how crops could survive on very little moisture giving them confidence to keep going in 2006. They identified that controlling summer weeds early, with sheep for a short time to retain residue levels, was a key.
Combining early sowing with a good stubble cover from the previous season and an effective summer weed control program, Wes Bakers was able to conserve much of the summer moisture. Averaging 1.9 tonnes per hectare he is happy with their results as they’ve been able to use all the moisture available.
Lesson 5: Keep your sowing rate up (compensate for the dry conditions)
Some growers around the state finished up with very low plant establishment counts as they reduced seeding rates to match crop density to moisture availability. The reduced establishment rate due to the dry seedbed amplified low plant numbers.
Plants per unit area – and number of tillers produced – dictate yield. When plants are under severe stress, one of the first things aborted is the last tiller. When this occurs, as was the case for many growers last year, the crop is only capable of achieving very low yields, even if good rains came later.
It is important to establish an appropriate plant density to set up a yield potential leaving you with the option of playing the season, if conditions are favourable.
Reduced rates can be a good option in regions where there is little moisture, either by low rainfall or through shallow soils. Match your seeding rate to the yield potential of the site – 40 plants per tonne of yield potential targeted per hectare.
For more information contact Mike Ashworth, WANTFA on (08) 9622 7557
Email: mike.ashworth@wantfa.com.au