Ameliorating duplex soils in the wimmera: three years later

By Kate Finger
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 Take Home Messages

  • Nutrition and soil compaction were the biggest limitations to crop production on a duplex soil at Netherby.
  • The positive yield response from ripping and spreading duck manure or balanced fertiliser lasted two seasons.
  • It is important to carefully consider the costs associated with any soil amelioration strategy, as any increase in yield and associated income can quickly be eroded by product and application costs.

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. They include identifying poor performing parts of paddocks and looking for ways to improve production.

Soil constraints are one possible reason for less productive areas. In 2020, BCG and the Wimmera Catchment Management Authority began a long-term soil amelioration trial at Netherby to explore a range of soil amelioration techniques and assess their impact on crop production; 2022 was the third year of the trial.

Established in a typical west Wimmera sand over clay (duplex soil), the trial area at Netherby had a severe compaction layer at a depth of 15cm (confirmed by penetrometer readings) and soil tests revealed it was lacking key nutrients to support crop growth. Topsoil in parts of the paddock also had non-wetting characteristics.

Aim

To investigate the long-term response of deep ripping, claying and spreading duck manure on a constrained duplex soil in the Wimmera.

Paddock Details

Location: Netherby

Soil type: Sand over clay

Paddock history: 2019: Vetch hay

Treatments: Refer to Table 2

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 pest 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 in early April 2020 to a depth of 30cm. The clay and manure treatments were spread on 14 April 2020 and cultivated into the soil on the same day. The site was cultivated again on 5 May 2020 after a rain event to further incorporate the clay. The duck manure was analysed for nutrient content and balanced synthetic fertiliser treatments of nitrogen and phosphorus were created (Table 4). The balanced fertiliser treatments were broadcast and incorporated by sowing with Scepter wheat on 25 May 2020.

Each year, in-season assessments included crop establishment counts, NDVI and crop biomass. The plots were also harvested to assess yield and grain quality parameters.

Results & Interpretation

2020–2021 results

Applying nutrients as either duck manure or balanced fertiliser plus ripping, increased wheat yields in 2020 and barley yields in 2021. Claying decreased yields in 2020, which was possibly due to the difficulties in incorporating it on a plot scale, and in 2021 there was no difference to the control.

Ripping had no effect on crop biomass in 2020 and 2021 but duck manure, balanced fertiliser and claying did, with the higher rates of nutrients (either via duck manure or fertiliser) significantly increasing crop biomass in comparison to the control. Claying resulted in less biomass than the control in 2020 and was comparable to the control in 2021.

For further details, see BCG Season Research Results for the 2020–2021 growing seasons.

2022 results

Ripping had no significant effect on crop establishment, crop biomass at grain fill, yield or the grain quality parameters we tested. This suggests that after three years the yield benefit from ripping to ~30cm has run out. It might also be the case that relatively ‘wet’ seasons in 2021 and 2022 meant the crop did not need to access moisture and nutrients beyond the compacted layer in the soil profile. If the seasons had been drier, the result might have been different.

The soil amendments no longer recorded significant differences in crop establishment, biomass, yield, and grain quality parameters tested, except for grain protein. Claying and the control had significantly higher grain protein than duck manure rate 2 and 3, and balanced fertiliser treatments (Figure 1). A possible explanation is that over the years the increased yield and biomass generated from the manure and balanced fertiliser treatments caused higher demand for nitrogen from the crop. Nitrogen was not applied in-season so the crop has potentially started mining the soil of nitrogen. At the time of writing, soil test results were not available to confirm this theory.

Commercial practice and on-farm profitability

Three years of data exploring a range of soil amelioration strategies on a duplex soil at Netherby has shown nutrition and compaction were the biggest limitations to crop production at the site. Claying appeared to be an unsuitable amelioration strategy as it had a detrimental effect on yields in the first year and no effect in subsequent years. This highlights the importance of correctly identifying the soil constraint/s and choosing the most appropriate amelioration strategy. Failure to do this results in wasted time and money if no returns are realised.

The economics of applying soil amendments and ripping in this trial are outlined in Table 3. The ripped 20t/ha duck manure and 20t/ha balanced fertiliser treatments generated the most income in this experiment (Table 5).

After taking into account product and application costs, even with the yield gains achieved at Netherby, none of the amelioration strategies come out ahead financially (using the costings in Table 6). Growers are encouraged to take the time to calculate costs for their own specific location and equipment, given variability in pricing and application of these amendments.

Before implementing any of these soil amelioration strategies, it also important for growers to be confident of a result across the paddock. See Maddern (2021) and Taylor (2021) for information about identifying suitable soil types and which amelioration strategy to use. Test strips are highly recommended before launching into a full soil amelioration program. This will help you work out site‑specific production gains and the maximum costs for it to be profitable.

~ as at April 2020 on index mundi https://www.indexmundi.com/commodities/?commodity=triple-superphosphate&months=120&currency=aud. % as stated in the SARDI Farm Gross Margin and Enterprising Planning Guide 2020. * assumes a product cost of $4/t (Adcock et al., 2009). ^assumes travel for 25t of product over 100km = $300 (Adcock et al., 2009). # as estimated in Bryce (2020).

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, Ripping, manuring and clay spreading on a duplex soil: early learnings from the first-year response, 2020 BCG Season Research Results, Birchip Cropping Group, Birchip, pp. 83–91.

Taylor J., 2022, Long-term responses to soil amelioration in the Wimmera, 2021 BCG Season Research Results, 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 Robinson family for hosting this trial.

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