Ameliorating sandy gravel soils in the Wimmera: four years later

By Kate Finger
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 Take Home Messages

  • Ripping as a soil amelioration technique should only be undertaken if soil compaction is a constraint.
  • On sandy gravel soils in the Wimmera, with no chemical constraints, chicken manure has proven to be a valuable soil ameliorant with a 1t/ha yield improvement over the control occurring four years after application.
  • Chicken manure at an application rate of 20t/ha has generated the most income and been a profitable exercise over the four-year experiment period in comparison to the control, claying and ripping.

Background

With land prices at record highs in recent years, generating more income from the same area of land is becoming more and more critical for farms to remain profitable. A multitude of approaches exist for growers to try and achieve this, including the identification of poor performing parts of paddocks and looking for ways to improve their production.

Soil constraints are one possible explanation for less productive areas. In 2019, BCG and the Wimmera Catchment Management Authority began a long-term soil amelioration trial in the southern Wimmera to explore a range of soil amelioration techniques and assess their impact on crop production; 2022 was the fourth and final year of the trial.

Located at Lubeck on a typical Wal Wal sand (coarse sand with ribbons of clay from 40cm), the trial area was selected because it had consistently underperformed. Soil testing showed the site was not chemically constrained, so a ‘kitchen sink’ approach was applied to investigate which, if any, of the common soil amelioration strategies could boost crop production at the site.

Aim

To investigate the long-term response of ripping, claying and spreading chicken manure on a constrained sandy gravel soil in the Wimmera.

Paddock Details

Location: Lubeck

Soil type: Sandy gravel

Paddock history: 2018: Barley

Treatments: Refer to Table 3

Seeding equipment: Knife points, press wheels, 30cm row spacing

Replicates: Four

Trial Details

Soil amelioration: Refer to Table 3

Fertiliser: Refer to Table 2

Trial managed as per best practice for pests, disease and weeds.

Method

A replicated split-plot trial was sown with main plots for ripping/unripped and the subplot randomised for soil amendment treatment (Table 3). The trial was ripped to a depth of 30cm on 26 March 2019.

The chicken manure and clay were spread on 6 June 2019, the day before sowing. Each year, in-season assessments included crop establishment counts and NDVI as well as crop biomass at flowering in the last two years of the experiment. The plots were also harvested to assess yield and grain quality parameters.

Results & Interpretation

2019–2021 results

Crop yields increased at Lubeck after applying chicken manure at 20t/ha each season. Ripping had no effect and claying was comparable to the control except in 2021 when it yielded better but not as much as the chicken manure.

Ripping had no impact on crop biomass in the year it was assessed (2021) however the chicken manure produced more biomass at late flowering than the clay treatments and the control.

It’s also worth noting that both ripping and spreading clay negatively impacted crop establishment in the 2019 and 2020 seasons. Crop establishment in 2021 was also affected by ripping.

For further details, please see BCG Season Research Results for the 2019–2021 growing seasons.

2022 results
Ripping

Plant establishment was negatively impacted by ripping (Table 4), but establishment was not correlated to yield (r² = 0.01). This ongoing negative impact on crop establishment suggests there are might be issues with sowing depth. Another potential explanation is that something from the subsoil has been brought to the surface, although this is unlikely as soil tests revealed the subsoil at Lubeck is chemically benign.

Ripping resulted in no biomass or yield differences (data not presented) which suggests subsoil compaction is not a major constraint for this soil type — no effect on yield has been recorded since the trial was established in 2019 (note this has not been confirmed with penetrometer readings as conditions in 2019 were not suitable for this assessment).

Ripping caused no differences in grain protein or screenings (data not presented). A difference in test weight was observed, with ripping resulting in an average test weight of 77.3kg/hL which was significantly more than the not ripped, 76.4kg/hL (P=0.035, LSD 0.8, CV 1.6%) but both met top-grade grain quality standards for wheat.

Soil amendment

Soil amendment continued to affect crop establishment.Clay treatments averaged 16 plants/m² less than the control (P=0.04, LSD 14 plants/m², CV 13.5%) but establishment was not correlated to yield (r² = 0.010). This indicates poor incorporation of the clay at the time of application is still impacting crop establishment. Even four years after application, at the plot scale the clay treatments have a more raised soil bed than the other treatments. This may be causing issues with sowing depth when using our plot scale equipment. Soil conditions at the time of crop emergence were ideal, ruling out hardened clay as a possible cause. Growers should therefore be mindful of achieving good incorporation with the soil when clay spreading. The straight chicken manure treatment had no impact on crop establishment.

Grain yield continued to be affected by soil amendment, with the chicken manure yielding significantly more than the control and the straight clay treatments (Figure 1). This is an impressive response from the chicken manure that was applied in 2019 and suggests nutrient supply was the biggest limiter of crop production on this soil type. Post-harvest soil sampling will investigate the nutrient status, soil carbon and microbial activity under the different treatments, but results were not available at the time of writing.

All grain quality parameters tested were significantly influenced by the applied amendments, with the 200t/ha and 300t/ha clay treatments having higher screenings (averaging 4.4 per cent) compared to the chicken manure treatments (averaging 3.3 per cent) (P=0.002, LSD=0.7%, CV%=18.3). The clay treatments also had lower grain protein (Figure 2) and lower test weight than the 20t/ha chicken manure treatment (data not presented).

Commercial practice and on-farm profitability

Four years of data exploring a range of soil amelioration strategies on a sandy gravel soil at Lubeck has demonstrated nutrition was the biggest soil constraint for crop production. Better yields than the control occurred every season, with chickpeas rising 0.2t/ha, wheat 1t/ha and 1.1t/ha and barley 2t/ha. The chicken manure treatments also produced substantially more crop biomass when assessed (2021 and 2022) and had no effect on crop establishment or negative impact on grain quality parameters when compared to the control.

Claying was not the solution. Its effects were either negative or zero on crop establishment and grain quality parameters throughout the 2019 to 2022 seasons. The only yield improvement over the control was in 2021. The clay potentially had time to disperse further through the topsoil and the crop was able to make use of this increased water holding capacity during the dry winter. This result did not continue into 2022, when the clay treatments yielded the same as the control. This is perhaps due to the exceptionally wet season of 2022, when there was no need for the plants to draw on additional stored water in the topsoil by the clay.

Ripping was also not the answer to boosting crop production in this poor performing part of the paddock. No effect on crop biomass or yield was recorded across the four seasons. Ripping also consistently had a negative impact on crop establishment, potentially a by product of a disturbed soil bed. If ripping is identified as an appropriate soil amelioration strategy, growers should be mindful of the importance of crop selection and proper preparation of the seeding bed to minimise impacts on crop establishment in the first and subsequent seasons. See Maddern (2021) and Taylor (2021) for further information about identifying suitable soil types and which amelioration strategy to use for the best result. Ripping, manuring and clay spreading as soil amelioration can be a costly exercise.

Table 5 outlines an estimate of some of the costs associated with undertaking various soil amelioration techniques. Growers are encouraged to take the time to work out these costs for their own specific location and equipment, given the variability in pricing and application of these practices.

When taking product and application costs into account (as outlined in Table 5), along with the total income generated from the different treatments (Table 6), applying 20t/ha of chicken manure was the most profitable soil amelioration practice to implement over the lifetime of this experiment.

References

Adcock D., Armstrong A., Best F., Chittleborough D., Imhof M., McDonald G., McNeill A., Nutall J. and Wilhelm N., 2009, Economic guide for on farm decisions, Subsoils Manual – 2009, Chapter 9, pp. 79–86.

Bryce A., 2020, It is important for growers to know the costs and benefits of dry ripping, GRDC Groundcover Western Region, Issue 145, March-April 2020, <https://groundcover.grdc.com.au/agronomy/soil-and-nutrition/is-it-ever-too-dry-to-rip-latest-advice-offers-tips-for-decisionmaking#:~:text=Operating%20costs%20for%20DIY%20ripping,and%20quality%20of%20the%20rip> [accessed on 23 January 2023].

Davenport D., Masters l., Stanley M., Masters B., 2015, Clay spreading and delving, Grains Research and Development Corporation Fact Sheet, <https://grdc.com.au/__data/assets/pdf_file/0017/142550/grdcfs-clayspreadingdelving-south_hr-pdf.pdf.pdf> [accessed 26 January 2022].

Maddern K., 2021, Investigating soil amelioration techniques in sandy gravel soils in the southern Wimmera, 2020 BCG Season Research Results, Birchip Cropping Group, Birchip, pp. 92–98.

Taylor J., 2022, 2021 BCG Season Research Results, ‘Long-term responses to soil amelioration in the Wimmera’, Birchip Cropping Group, Birchip, pp. 56–65.

Acknowledgements

This research was funded through the Australian Government’s National Landcare Program, with support from the Wimmera Catchment Management Authority.

We thank the Taylor family for hosting this trial.

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