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Quantifying the effect of paired-row systems on weeds and crop

In 2005 Dr Jack Desbiolles, senior agricultural research engineer at University of SA led research into the effects of seedbed utilisation and seed rate on weed competition and wheat yields on a shallow grey Mallee loam near Minlaton in South Australia.

The SAGIT funded research, in collaboration with the Southern Yorke Peninsula Alkaline Soils Group, centred on investigating the impact of seedbed utilisation (SBU), which quantifies the extent of the row spacing occupied by the crop. Low SBU seeding typically makes a uniform seeding job easier to achieve but there is an increased risk for fertiliser toxicity to reduce seedling emergence, and inter-plant competition can significantly limit the yield potential in higher potential seasons.

Dr Jack Desbiolles’ research favours the adoption of paired-row seeding systems as a practical way to benefit from higher seedbed utilisation. Photo: Birchip Cropping Group (BCG)

Two wheat crop seeding rates were tested – ‘Standard’ seeding rate of 88 kg/ha to establish 180 to 190 plants/m2and ‘High’ seeding rate of 125 kg/ha to establish 250 to 260 plants/m2. Three levels of seedbed utilisation (SBU) were trialled and Marloo oats was broadcast at 40 kg/ha (105 seeds/m2) and incorporated using a prickle chain on the ‘weedy’ plots to simulate weed competition.

A knife blade plus double-shoot rubber seed boot on 25 cm row spacing gave low (15 per cent) SBU. The intermediate treatment was 45 per cent SBU using a double shoot narrow ribbon Anderson opener, also on 25 cm row spacing. Full (100 per cent) SBU was applied using a 20 cm wide share with a 20 cm reach plus Morris spreader boot set on 20 cm row spacing, effectively sowing seed across the full bed area and leaving no inter-row space.

While crop seeding rate had little effect initially, the 100 per cent SBU had a significant effect on early weed vigour. This treatment reduced weed biomass by 16 to 20 per cent, and reduced weed tillering by 25 to 30 per cent in the early stages of growth.

Increasing seedbed utilisation from a common 15 per cent (left) to 100 per cent (right), especially when combined with higher seed rate, effectively suppressed weed biomass and seed production while significantly increasing crop yield.

SBU also had an impact on later weed growth where greater SBU proportionally reduced weed biomass by 11 to 14 per cent (in the 45% SBU system) and 29 to 32 per cent (in the 100% SBU system). A 43 per cent reduction in weed growth was achieved using a high seeding rate combined with 100% SBU.

Weed seed production followed similar trends, with the best results being a 38 per cent reduction in seed weight per weed plant using full SBU and the higher seeding rate. Following a 289 mm rainfall growing season, the full SBU seeding combined with high seed rate increased wheat grain yield by 0.43 t/ha (in a weed-free environment) and 0.83 t/ha (in a weedy environment), relative to the low SBU, low seed rate control.

This research confirmed the principles of crop competition and showed that paired-row systems were a practical option to help achieve greater weed competition and higher yield potential through greater seedbed utilisation.

More recently, Dr Desbiolles conducted research on different soil types in the Murrayville district (Vic) in collaboration with Mallee Sustainable Farming Inc, and with DAFF funding, comparing paired-row systems to a commonly-used single row knife point system. In this trial, the paired-row systems gave the highest and most consistent crop establishment across a swale-dune Mallee sandy soil system, with good moisture conditions at seeding and sufficient in-crop rainfall.

The plant establishment benefits ranged from +15 per cent on the mid-slope and sand hill, to +20 per cent on the sandy stony flats, relative to a district system control, and after a dry season finish, achieved up to 0.15 t/ha gain in wheat grain yield.

“These results correlate well with the earlier work done in Minlaton which measured crop yield and weed suppression benefits through increased seedbed utilisation,” he said. “Improving crop establishment and gaining the crop competitive advantages relies on correct seeder set-up.”

In a review of seeder set-up for the GRDC Stubble Management project, Dr Desbiolles highlighted the following considerations when it comes to using paired-row systems in different situations:

  • Recommended for use in marginal soil moisture conditions when seeds can be placed onto undisturbed soil moisture.
  • Recommended for effective incorporation of pre-emergent herbicides (IBS) application. Crop safety is best secured using paired-row attachments closely integrated behind the opener.
  • Possible use in stony soils if compatible with shallow operating depth.
  • Possible use in non-wetting poor fertility soils, where seeding is at furrow tilling depth.
  • Possible use under rhizoctonia pressure if coupled with best practice disease management.
  • Possible use in high residue situations when coupled with good residue management strategies.

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