The strategic use of tillage in conservation farming

Mark Conyers,

NSW DPI, Wagga Wagga Agricultural Institute.

GRDC project code: DAN00152

Keywords: cultivation, soil management, soil structure.

Take home messages

• Current advice to farmers on soil tillage management contains apparent contradictions. More flexibility is required in the application of conservation farming practices in commercial farming.
• We are evaluating the impact of a single tillage on soil chemical, physical and biological properties. We are then assessing the time required for the soil to recover from any detrimental impacts of a single, strategically applied tillage.
• Current data suggests that soil physical properties suffer measurable but minimal damage from a single tillage, and the bulk of the recovery takes place over one to two years.

The issue

Conservation farming involves reduced tillage, stubble retention and good rotations. This underpins sustainable grain production systems worldwide. However, problems arise when complete zero tillage is made the centre of the farming system.

• On one hand we are encouraging farmers to adopt zero tillage. On the other hand we are advising farmers that limestone has to be incorporated into the soil or else it does little to ameliorate acidity.
• A lack of tillage causes nutrients such as phosphorus and organic nitrogen to accumulate on the soil surface where they can be less accessible to plants due to extremes of temperature, such as sub zero to >50°C, and because of soil drying.
• Zero tillage can favour diseases such as Rhizoctonia and Pseudomonads around the roots of some species and cultivars. Additionally, conventional tillage has been found to suppress plant parasitic nematode populations compared with direct drilling.
• Tillage can be used to lower numbers of snails and slugs prior to canola crops, and to lower mice numbers in affected fields.
• Integrated weed management might require the use of strategic tillage to manage herbicide resistance. In mixed farming systems, grazing the pasture phase can be used to minimise weed burdens but for continuous croppers, or in the cropping phase of mixed farming, some tillage might be needed for integrated weed management.
• Hardpans can be removed by deep ripping.

Therefore from an overall farm management perspective, limited and strategically timed tillage could form part of a productive, sustainable system.

The central question emerges:

How much damage is done to soil by occasional tillage, strategically applied, in an otherwise no-till system? If damage is done, how long does it take the soil to recover?

Objective

To resolve the contradiction in current advice to farmers and provide practical best management practice guidelines for tillage.

What we are doing?

We are investigating this problem based on the hypothesis:

The agronomic and economic benefits of a strategic tillage operation exceed any agronomic costs due to damage to soil structure. The net benefits will accrue from such factors as lime incorporation, the homogenisation of stratified nutrients, disease and pest control, and weed management.

The outcome will potentially be more flexibility in the implementation of conservation farming practices, i.e. a ‘horses for courses’ approach to tillage management dependent upon circumstances, - paddock, season, and/or resources.

Basic design

Main plots: no-till (ongoing), non-inversion tillage (scarifier), partial inversion tillage (offset discs or rotary hoe).

Split plots: ± NPS nutrients onto retained stubble for C sequestration.

Site or year dependent split plots: ± stubble, or year of tillage.                                                  

Reps: n =4.

Basic measurements

Agronomic: grain yield (plus oil, protein), anthesis DM, establishment counts.

Meteorological: rainfall, air and soil (10cm) temperatures, etc.

Chemical: Soil C, total N, Colwell P, pH (plus site characterisation- ECEC, EC); plant N (anthesis DM and grain).

Physical: Soil bulk density, hydraulic conductivity (saturated and -4 cm), wet aggregate stability (WAS) (plus site characterisation - pF, psa profiles).

Biological: disease organisms, e.g. Rhizoctonia.

Team members

Farmers: Geoff and John Byrne, Chris Holland, Andrew Simpson.

Consultants: Peter McInerney, Greg Hunt, Sandy Biddulph.

Farmlink Ltd: Cindy Cassidy.

CSIRO–Plant Industry: John Kirkegaard, Clive Kirkby, Andrew Bissett, John Graham.

Charles Sturt University: Phil Eberbach.

DPI NSW: Kurt Lindbeck, Vince van der Rijt, Albert Oates, Graeme Poile.

Sites

Harden CSIRO Long Term Trial

The no-till plots that had long term stubble retention or stubble burnt have been split for ongoing no-till versus the rotary hoeing of the previously no-till soil.

The split plot has been further split for ± NPS supplementary nutrients for increasing the store of SOC; in 4 reps, = 32 plots.

Berthong (N of Cootamundra) Geoff and John Byrne

The beauty of what we were able to do here was two having paddocks side-by-side with the same history but one came out of lucerne pasture into crop in 2012 and the other came into crop in 2013.

2012: no tillage, scarifier, off sets, ± NPS; in 4 reps, 24 plots; then

2013: no tillage, scarifier, off sets, ± NPS; in 4 reps, 24 plots.

This way we capture the effect of the year of tillage at the site, both following lucerne pasture.

Thuddungra (Young-Grenfell) Chris Holland

Here we were able to capture the impact of cultivation during a cropping phase, post wheat and for liming of canola in 2012.

2012: no tillage, scarifier, off sets, by stubble retained or burnt, ± NPS for SOC; in 4 reps,               = total 48 plots.

Daysdale (NNW of Corowa) Andrew Simpson

This continuous cropping site had vetch brown manure in 2011, and it is occasionally grazed by sheep, causing compaction.  

2012: no tillage, scarifier, off sets, ± NPS; in 4 reps; then in

2013: no tillage, scarifier, off sets, ± NPS; in 4 reps, = 48 plots.

As at Berthong, we are able to capture the effect of the year of cultivation but in this case in a fully randomised design.

Results and discussion

We focus this report on the key soil physical property of WAS. This soil attribute indicates resistance to breakdown of soil peds into dust (particles < 50 microns) and hence susceptibility to wind and water erosion. Figure 1 shows the results from the first site established, the Harden long term site of CSIRO (Kirkegaard and Kirkby, CSIRO). The top line shows the data for ongoing soil management with direct drilling and stubble retention, DDSR, hollow triangles. The filled diamond symbols to the upper left show the WAS for a 5 year old commercial pasture surrounding the trial site. The data form a good benchmark for assessing the impact of a strategic tillage.

Figure 1. The time course of wet aggregate stability under four continuous cropping treatments (DD = direct drilled, RH = rotary hoed, SR = stubble retained, SB = stubble burnt), a surrounding 5 year old pasture in 2011 (old Pasture), and a strip of pasture sown after the soil was rotary hoed in wet conditions (late RH). 

A single rotary hoeing (filled and hollow circles) caused a decrease in WAS of only five to 10 per cent. We added a treatment beside the main trial in May where we undertook a rotary hoeing when the soil was wet (filled squares). This caused a decrease in WAS of approximately 15 per cent. Hence a single tillage of a relatively severe nature caused measurable damage to soil structure. However, as can be seen in Figure 1, most of the loss of soil structure was compensated for during the following 12 months under a sub-clover pasture. For the four treatments in the main trial under continuous cropping, there appears to be a small residual detriment to WAS, approximately seven per cent, that remains slow to return to the pre-cultivation level.

The results will become clearer during the final two years of data collection, with an estimated completion and reporting date of September 2016. As this is a long term issue, we are not offering short term advice based on results to date.

Contact details

Mark Conyers

Wagga Wagga Agricultural Institute, NSW DPI

PMB Pine Gully Road, Wagga Wagga NSW 2650

02 69381830

mark.conyers@dpi.nsw.gov.au