The less frequent and lighter winter rainfalls much of the Australian wheatbelt has had in recent years, have tested the water-storing capacity of our cropping soils. Shallow soils with less stored water – or a smaller ‘bucket’ – have induced frequent drought stress, especially in warm and windy conditions. But larger distance between plant rows (around 0.5 m) can provide a zone of moist soil which is accessible during the later part of drought stress periods (see photos opposite and Figure 1).
Seeing better edge-row growth in dry seasons has encouraged Australia-wide pursuit of benefits from wider or skip row sowing systems in southern Australia.
We have often induced more drought stress in our cereal crops on shallow soils by using higher seeding rates and narrower rows to help control grass weeds. Lower seeding rates and wider rows are the main tools to reduce drought stress, so we need to use the other grass control tools more effectively. A well managed pasture–crop system may be one of the easier of the more ‘grass safe’ situations to use wider rows and lower seeding rates.
There have been numerous trials and on-farm tests of wider rows and lower seeding rates. We can already see how the wide inter-row provides new farming system opportunities such as barley grass control in barley by inter-row shield spraying, relay planting, in-crop deep ripping and soil amendment. Very wide row methods are relatively easy to use on-farm and at little cost.

What have the trials shown us?
Most of the Western Australian trials have been at Pindar, east of Mullewa in the northeast of the wheatbelt. Mike and Deb Kerkmans generously hosted these 2003 through 2005 trials at ‘Marlingu’. Marlingu has soil with shallow rooting depth over rock, gravel or saline layers.
The 2003 and 2004 seasons had periods of dry weather inducing drought stress while 2005 had a classic example of mid-winter drought stress. There were excellent conditions for early growth from April 2005 to the end of June, then six weeks of little rain and some very hot dry days.
Arrino was the most commonly used wheat variety during those years. Figure 2 summarises the effects of wider row spacing and lower seed rates on yields for Arrino at Pindar and compares other cases.
The benefits at Pindar were normally in lower yielding years and situations where drought can be induced. In almost all cases we found grain quality benefits with wider rows. In one case in 2006 it moved the wheat grade from AGP to ASW.
But the yield effect is variable and very dependent on:
Maximum rooting depth not too shallow to suffer considerable evaporation loss from the inter-row, nor too deep to reduce root access to deeper soil moisture (Figure 1);
Sufficient crop nutrition to provide enough tillers for optimum yield (so nil fertiliser during the pasture phase is a poor choice, for example, Pithara 2006 in Figure 2); and,
Sufficient large early biomass (early sowing and good rains in May and June) followed by drought stress. This suggests opting for early sowing and high crop nutrition strategies.
Results from Ben Jones’ wide row research in the Victorian Mallee found less yield benefit than seen at Pindar – but had better yields and screenings results in barley and triticale than wheat in low rainfall years. Ben found more income stability year to year with wide row systems and concluded that 400 mm rows with ribbon sowing may be the best compromise in the Mallee environment.

The severe winter drought stress effects at Pindar in 2005 on the more fertile (50 ppm available P and 1.4 per cent organic matter) sandy clay loam are shown in the photographs on the previous page. The trials were DBS (deep banded system) sown on a two year old fallow with MAP deep-banded at 55 kg per hectare.
The yields of the varieties with similar flowering dates (Figure 4) show that the combination of very wide rows and low seeding rate provided the most benefit. There was a 450 kg per hectare yield benefit over the 300 mm rows at a 70 kg per hectare sowing rate. Reduced seed rate alone provided about 270 kg per hectare yield benefit.
The easily visible head damage showed that the wider rows and lower seed rate protected the crop more from drought stress – and conserved more yield.
During the 2005 Pindar trials, part of the Arrino crop was irrigated with 10 mm during each week of the mid-winter drought. By the end of the growing season, this part of the Arrino trial had an additional 65 mm of water. The average yield of the row and seed rate treatments was 3.8 tonnes per hectare – or about 18 kg per mm of growing season rain and 40 mm of stored moisture.
This suggests that the six week drought and associated stress was the main constraint to the dryland crop yield.
In terms of variety responses to very wide row systems in the Pindar 2005 trials, the least yield benefit to 600 mm rows came from Kalannie, because it began flowering before the drought stress. The latest flowering variety Janz, showed a yield benefit similar to other varieties which flowered during the drought stress.
The stress induced some heads to be trapped in the boot of the flag leaf; this led to fungal staining due to the moist conditions after the mid-August 2005 rains.

Grain quality effects
The reduced drought stress from the wider rows and lower seed rate improved grain size and grains per head to compensate for the lower head density. But the timing of any finishing rains is significant.
A good September rain will generally allow better grain fill for all row width and sowing rate treatments. Our 2005 Pindar trials showed that despite some late rains, the very wide rows, lower seed rate treatments enabled most varieties to have reduced screenings, especially if the variety already had poor grain fill.
Effects on protein by increasing row spacing and reducing seed rate was generally negative, but small. There was an average protein loss of 0.4 per cent across nine varieties and a maximum loss of 1.7 per cent protein for Arrino.
Effect on gross margin of the varieties was calculated using 2005–06 prices for Cunderdin, Bonnie Rock, Wyalkatchem, Drysdale, Arrino, Westonia and Tammarin Rock. The average gross margin benefit from very wide rows, low sowing rates over the 300 mm rows and 70 kg per hectare sowing treatments was $84 per hectare. This was based on variable costs of $132 per hectare for narrow and $124 for wide rows.

Ribbon sowing
Increasing the spacing between plants within the row by ribbon sowing or using twin rows, should enable the cereal plants to develop more freely in search of scarce resources in dry seasons. Trials by Amjad and Anderson at Salmon Gums, WA during the 2002 drought showed a clear trend for cereal yield from wider rows to increase as band width within the row increased.
This suggests in dry seasons a good strategy is to employ ribbon sowing and appropriate wide press wheel systems. Leaving a loose soil layer over the base of the furrow, by a chain or grading rubber flap, will also help reduce soil moisture loss from the seed bed.
Jack Desbiolles of the University of South Australia, has shown that ribbon seeding can be optimised in the Mallee environment by using 500 mm row spacings, compared to 250 mm row spacing, and seed rates equivalent to about half normal rates.
Trials in 2006 at Tardun, near Pindar, found about 14 per cent more wheat yield with 80 mm ribbon width, compared to 30 mm seed band width in a dryer season than 2005 and shallow rooting depth.
So there is a strong case that potential benefits of cereals on wide row systems will not be realised if ribbon sowing is not used in the seeding system.

Weed control by inter-row shields
There is a lot of information on inter-row shields, but improvements to reliability and work rates for large areas are still needed. From a systems point of view, it is encouraging to note that an on-farm trial in 2005 near Merredin WA, found a glyphosate application between very wide rows of wheat was as effective in grass weed control as a chemical fallow – yet much more cost effective. An added bonus was the harvesting of 1.2 tonnes per hectare of hard wheat to offset the spraying costs.
If the fallow is mainly to control grass weeds, then very wide rows of wheat and shield spraying could be a valuable tool in the whole low rainfall farming system. Less bare annual fallow will reduce deep drainage.
In a grazing-free low rainfall farming system, inter-row herbicides may be an essential tool to help control grass weeds. Shield spraying technology is becoming more developed and more inventive. Shield sprayed cereals for grass control can be a useful part of the cropping system, even for situations without significant drought stress.

Some downsides
Under some circumstances, yield may be lost in the very wide row system compared to normal row spacings and seed rates. These circumstances include:
Late (June–July) sowing in southern grain growing districts; due to less vigorous early growth to use water and induce drought stress (see points for Eyre Peninsular and Pithara 2006 in Figure 2). The late growth development and short season may result in unused inter-row moisture in the wide rows, especially with late season rains (Figure 4).
Uniform fertility from a pasture legume phase or green manuring; the wider row spacing will disadvantage nutrient access, compared to narrower rows.
Poor tiller development, due to relatively low fertiliser use (for example, Bencubbin 2006 in Figure 2).
Increased rainfall or rainfall frequency.
Volunteer pasture legumes which will compete for inter-row soil moisture.
Wheat varieties which may compete poorly with low levels of grass weeds (for example, Wyalkatchem and Bonnie Rock in our trials).
Back-pressure effects in the air seeder when alternate tubes are blocked. Seed or fertiliser rates may be reduced.
Increased soil erosion risk can also occur after a crop of wide row cereal sown on poor cover. The unsown inter-row can be very erodible, compared to the stubble row from the harvested crop.
In some cases these yield losses may be outweighed by weed control, soil amelioration or other benefits from the very wide row system.
Acknowledgements: Funding support from NLP with the Liebe Group, assistance from Stewart Edgecombe, Stephen Davies, Bill Bowden, Sylvain Pottier, Tony Vyn, Lyle Mildenhall, Geraldton Research Support Unit, Mike Kerkmans, and Ben Jones.
For more information contact Paul Blackwell on mobile 0429 102 105 or
email pblackwell@agric.wa.gov.au