Assessing canopy management in CTF systems with farmer machinery

Greg Condon and Kirrily Condon,
Grassroots Agronomy, Junee, NSW

Introduction

 
The adoption of no-till farming and subsequent use of wider rows has attracted significant attention from researchers and farmers alike. Wide row spacings of 25, 30, 33.3 and 37.5cm (10” to 15”) using GPS guidance have been promoted in no-till, CTF systems to accommodate inter-row sowing for improved stubble handling capacity, increased safety with pre-emergent herbicides in cereals and a potential reduction in cereal diseases such as crown rot. The requirement for fewer seeding units is also seen as an advantage, as is the potential for moisture conservation in drier seasons.

There are, however, issues with wider rows such as a reduction in weed competition and lack of groundcover during winter which can increase evaporation losses. It is well documented that yield is reduced when row spacing is greater than 30cm and potential yield is greater than 3t/ha, due largely to a reduction in head numbers. However farmers are dealing with complex farming systems which involve compromises, so selecting a row spacing that minimises potential yield loss but maintains the ability to inter-row sow for stubble retention (and its associated yield benefits) is important.

It should be emphasised that row spacing is just one component of canopy management, with the ability to manipulate the canopy structure through plant density, nitrogen management and variety choice (eg. free or low tillering varieties) potentially having a greater impact on yield outcomes. Anecdotally, sowing early with a free tillering variety has proven to be an effective practice for compensating for wider row spacing. Regardless of the tools used, maximum yield potential won’t be achieved unless the basic agronomic practices, including summer weed control, sowing time, variety and nutrition are prioritised.

CTF systems are an emerging practice in southern NSW to complement no-till farming through minimising compaction and aiding stubble retention. By matching machinery working widths and axles (to the width of the header), all wheel traffic is confined to permanent tracks through the use of 2cm RTK guidance. The tracks mean wheeled compaction is limited to 10-15% of the paddocks, while the hard surface on wheel tracks also reduces horsepower requirements and fuel usage.

Permanent traffic lanes and matched sowing-harvesting runs in a CTF system are ideal for replicated research trials where repeatability and accuracy are able to be maintained in large scale plots using 2cm RTK guidance.

Finding the solution

 
To investigate how wheat responds to a range of canopy management strategies within a CTF system, trials were established near Coolamon and Junee in 2011 comparing row spacing, target density (sowing rates) and seeding units (disc and tyne) in the presence of standing stubble. Funded through the GRDC ‘Southern Agribusiness Trial Extension Network’, the trials used farm machinery to sow and harvest large scale replicated plots using RTK guidance. Inter-row sowing was used to implement the narrow row spacing treatments using 2cm guidance. Assessments were taken throughout the season by Grassroots Agronomy and Agritech Crop Research to measure establishment, tillers, dry matter (GS32 & GS92), yield, quality and harvest index.


Table 1 – Trial details

Results

 
Stubble retention in 2011 was a difficult exercise due to the late, wet harvest of 2010 which resulted in lodged crops and slow harvesting. By sowing time, many of these stubbles had rotted at ground level due to the wet summer, making inter-row sowing challenging as stubble pulled out easily during sowing. Consequently, many growers made a tactical decision to burn stubbles to ensure sowing time was not compromised.

Despite these difficulties, both trials were sown into standing stubbles using a CTF system, using a disc seeder at Junee and a tyne seeder at Coolamon. Sowing conditions were slightly better at the Junee site, where the header had been able to cut the stubble short. However occasional guidance issues at this site affected inter-row sowing of some narrow row spacing treatments. Trial establishment at the Coolamon site was excellent, with the CTF system being able to produce uniform row spacing treatments. Unfortunately mice damage reduced target plant numbers at this site.

a) Junee – disc seeder
Plant density and row spacing had no significant effect on yield at the Junee trial. It was interesting to note, however, that although the ‘highest density’ canopy (narrow row, high plant numbers) produced significantly more heads, the plants compensated by producing fewer grains per head to effectively cancel each other out and provide no yield response. Variety may have been a limiting factor in achieving yield potential in this trial, with the Ellison only averaging 3.9t/ha compared with Gregory at 4.5t/ha in the same paddock.

b) Coolamon – tyne seeder
As with the Junee trial, significant differences in plant density had no effect on yield, despite greater head numbers at the higher plant population. Row spacing did, however, significantly affect yield, with a 0.2t/ha yield response at the narrow row spacing.

Discussion

 
Row spacing and canopy management trials have historically been conducted in isolation from other components within no-till farming systems, such as inter-row sowing, stubble retention, disc seeders or knife point/press wheel configurations. The repeatability and accuracy of CTF systems means canopy management principles can be assessed in commercial no-till situations using large scale, replicated plots.

In this project, there was a significant effect of row spacing on yield at the Coolamon trial with a tyne seeder, but not to the degree often observed in small plots trials. Row spacings wider than 30cm have been proven to yield less when potential yields are greater than 3t/ha due to reduced head numbers. Crop competition with weeds is also reduced at wider row spacings and the impact of herbicide resistance, particularly when continuous cropping, warrants careful consideration when assessing row spacings. Crop competition is an important component of integrated weed management to ensure the sustainability of herbicides such as glyphosate and trifluralin in no-till systems.

The lack of response to plant density in either trial supports considerable data and paddock observations, where lower plant numbers are still able to achieve target yields through the plant’s ability to compensate by producing more tillers/heads. However the ability to compensate is limited as the sowing window gets later or nitrogen is lacking. In this case, increasing target plant densities from 50-80 plants/2 to 100-140 plants/m2 (depending on variety) may be warranted.

Growers engaged in no-till farming systems need to consider the important drivers of yield, WUE and profit. For many, the advantages of wider row spacings in no-till such as inter row sowing, stubble retention, improved crop safety with pre-emergent herbicides and lower machinery costs have outweighed any negative impacts. These factors, in combination with key management practices including rotations, summer weed control, timely sowing, nitrogen management and foliar disease control, ensure even at wider rows, yield and WUE have been at benchmark values, particularly in dry seasons. However for a system to be robust across a range seasons and in the context of challenges such as herbicide resistance, those engaged in no-till farming need to consider the value of narrow row spacings and how it can be potentially incorporated without compromising the proven benefits of the system.

Acknowledgements:

 
Tony Lehmann and family, “Hillside’, Illabo.
Matthew & David McKinley and families, “Arcadia Downs’, Coolamon

Justin Tidd, Tony Single, - AgriTech NSW
GrainCorp Junee
James Hunt – CSIRO Canberra

Contact details:

 
Greg Condon
Grassroots Agronomy
greg@grassrootsag.com.au  
0428 477348