Guideline for growers
- There are both benefits and challenges that come from increasing row spacing to above 25cm in a retained stubble cropping system.
- Yield potential, weed competition, crop rotation, stubble loads, sowing efficiency, disease management, crop safety (from herbicides damage and fertiliser toxicity) and machinery costs and set-up should all be considered before settling on a row spacing.
One of the key considerations that can go a long way towards overcoming the challenges of sowing into a stubble retained system is modifying row spacing.
Compared to now, conventional farming systems were largely dominated by relatively narrow row spacing 6-7” (15-18cm) and small machines (4-8m). Over time, and with the wide adoption of stubble retained systems, there has been a shift to larger machines, and subsequently, a lot more residue to manage at sowing time. This is particularly an issue in the higher production areas in the Wimmera.
The challenge in the low rainfall zone (Mallee) is slightly different. Although there can be times where high stubble loads are present after good seasons, row spacing is more closely linked with pre-emergent herbicide efficacy, crop safety and operation efficiencies within stubble retained systems.
In 2015 a trial was established at Jil Jil in the Southern Mallee to determine if row spacing can be used to influence grass weed populations and growth, and the impact on crop performance.
Crops sown on narrow row spacings produced more biomass by anthesis, and resulted in higher yields in a weed free situation, with the 38cm (15”) row spacing treatment yielding 0.13t/ha less than the 22.5 and 30.5cm spacings (Figure 1). It has long been known that narrower row spacing increases yield, however this was believed to be less important in low yielding environments. The more uniform pattern of crop establishment present in 22.5cm and 30.5cm row spacing treatments probably resulted in greater radiation interception, reduced evaporative losses and increased dry matter production and yield. The full report from this trial can be found here or see references below.
What is the optimum row spacing for stubble retention?
There is no ‘right’ or ‘wrong’ row spacing in a stubble retained system. According to Victoria No-Till Farmers Association, “the best row spacing is the one that suits your individual farming system.”
The optimum row spacing will change with crop types, seasons, yield environments, weed burdens, soil type and, of course, machinery. Nevertheless, in stubble retained systems, careful planning and management is required to understand residue flow, seed placement, pests, disease management and herbicide efficacy (including soil throw and incorporation of volatile pre-emergent herbicides such as trifluralin) in order to support decisions about the most suitable row spacing.
According to Mallee-based consultant Simon Craig (Agronomise), the majority of Mallee farmers operating a retained stubble system were currently on 12” or 30.5cm row spacings while in the Wimmera spacings varied more from farm to farm. Wimmera agronomist Simon Severin said many farmers were still using row spacings below 25cm, mainly to account for more diverse crop rotations and weed species.
Across both regions however, there has been a trend toward wider spacings among growers who have aggressively pursued a no-till farming system. Row spacings above 25cm improves pre-emergent crop safety and enables most to inter-row sow and avoid blockage issues while minimising yield penalties that can be suffered by some crops when sown at spacings greater than this. Additionally, in drier years in the Mallee environment, crops sown at wider spacings can produce higher yields than those sown narrower, provided stored soil moisture is available during the later stages of crop development.
However, things are changing. An increasing incidence of herbicide resistant weeds, and the inability of commonly used pre-emergent herbicide trifluralin to work with disc seeding systems where there is minimal soil disturbance, has motivated growers to consider non-herbicide weed control options, including crop competition. The improved ability for crops sown on narrower row systems to out compete weeds in broadacre farming systems is proving a key motivator behind a move back towards narrower row spacings.
Table 1: Benefits and challenges of row spacing.
The implications of machinery type
To facilitate sowing into stubble, many farmers have modified conventional machinery to avoid the cost of purchasing specialised machinery. As well as tyne arrangement to facilitate wider row spacings, modifications include those to the tyne itself – increasing the height of the tyne and changing the shape of the tyne from rectangular to more circular to shed stubble more readily (Mead and Qaisrani, 2003).
Some of the problems associated with sowing can be overcome by purchasing new machinery or undertaking extensive modifications to existing machines. Disc seeders are less likely to block in stubble than tyned implements and allow growers to inter-row sow on narrower spacings. It should be noted, however, the cost of the machinery and amount of moving bearings often motivates growers who operate a disc seeder to use row spacings greater than 25cm.
The majority of farmers surveyed as part of this project in 2015 rated 15” (38cm) row spacings as optimal for a disc planter (Figure 2), however Vic No-Till Farmers Association (VNTFA) have since reported a recent trend towards narrower systems as machinery improves and growers gain confidence in its operation.
Crop type and row spacing
In cereals, there is enough research to conclude that in higher yielding environments, narrower row spacings will often out-yield the wider row spacings, while in drier years/environments, wider row spacings can out-yield narrower provided moisture is available to the crop post flowering. Broadleaf crops appear to be less sensitive to yield loss with widened row spacing than cereal crops and may benefit from wider rows in some situations. The exception to this is lentils with previous research suggesting that best lentil performance comes from sowing as narrow as feasible (ie < 30.5cm spacing) into standing stubble that can then act as a trellis for the lentils. This improves yield and harvestability as a result of a lower incidence of lodging (Pulse Australia, 2015).
Canola can also be successfully grown on wider row spacings without significant yield penalty, especially in the low-medium rainfall zones (Harries, M., 2015).
Have a plan and think about your crop types and their subsequent residues and how your rotation or crop sequence, coupled with row spacing may reduce some of the issues associated with stubble retention.
Angel, K., ‘Using sowing direction and row spacing for weed management in the Mallee’, BCG Season Research Results’, 2015. Accessed at: https://thestubbleproject.files.wordpress.com/2016/04/using-sowing-direction-and-row-spacing-for-weed-management-in-the-mallee-2015-bcg-srr.pdf
BCG, 2008 ‘Row spacing in a no-till system’, Flexible Farming Systems Project – Factsheet 1. Accessed at: http://www.bcg.org.au/cb_pages/publications.php
Harries, M., 2015 ‘Wider rows offer yield potential’, Ground Cover issue117 – Optimising canola profitability. Accessed at: http://www.grdc.com.au/Media-Centre/Ground-Cover-Supplements/Ground-Cover-Issue-117-Optimising-canola-profitability/Wider-rows-offer-yield-potential
Mead JA and Qaisrani, R (2003). ‘Improving stubble flow through tines on agricultural machinery’, Biosystems Engineering pp. 85, 299-306.
Pulse Australia, 2015 ‘Wide row pulses and stubble retention’, Australian Pulse Bulletin, Accessed at: http://www.pulseaus.com.au/growing-pulses/publications/wide-rows-and-stubble-retention
This research is being conducted by BCG as part of the GRDC Maintaining profitable farming systems with retained stubble initiative (project BWD00024 ‘Maintaining profitable farming systems with retained stubble in Victoria and Tasmania’).