Giacomo (Jack) Betti and Steve Davies (DAFWA)
|Contributor||West Midlands Group|
Site 10, Dandaragan, WA
To compare different clay spreading and tillage methods for the amelioration of water repellent soils.
The topsoil sand at Yanda was severely repellent (Figure 1, left), as measured by the molarity of ethanol droplet test (MED). Clay spreading and tillage (either combined or separated) significantly reduced the severity of water repellency. When the subsoil clay was not incorporated by tillage or was incorporated using an off-set disc, the soil water repellency generally decreased with an increasing amount of subsoil clay. However, low-repellency (MED<1) was obtained only at rates over 150 t/ha of subsoil.
In contrast, spading (either at standard speed of the tractor or at half speed) was the most effective method for the alleviation of soil water repellency. In these treatments, the MED values were completely reduced to zero (non-repellent soil) and, most importantly, this was achieved independently from the presence, or not, of clay-rich subsoil. The significant reduction of the soil water repellency however did not convert to better plant establishment measured five weeks after sowing (Figure 1, Right). This result could be explained by the wetter than usual weather recorded during April-May 2016 that reduced the impact of the soil water repellency on plant establishment. Nevertheless, tiller counts collected five weeks after plant counts showed a significant effect of tillage on the number of tillers. In particular, the spader treatments (standard and ½ speed) had the most tillers while the control had the fewest.
This trend was repeated with the barley grain yields at harvest time (Figure 2). Both tillage and rate of clay spreading, significantly improved grain yield in comparison to the control treatments (no clay and no tillage). The lowest yield were recorded in the control treatments and in the off-set tillage only (no clay) with an average of 1.41 t/ha and 1.36 t/ha respectively. The shallow tillage (or incorporation) using off-set discs did not yield significantly differently from the treatments with no incorporation at any given rate of subsoil clay. Clay spreading at 250 t/ha followed by spading at standard speed produced the highest yield on average (2.93 t/ha). Nonetheless, all treatments with spading (standard and ½ speed) were able to yield over 2.5 t/ha, even without the addition of subsoil clay (Figure 2).
Field observations showed that the trial was also affected by frost, which explained the lower than expected yields. Head samples were collected in early November 2016 from all the treatments (except spading at ½ speed) for the assessment of frost induced sterility (FIS= number of sterile florets / total number of florets) and the results are shown in Figure 3.
The results on FIS showed that frost damage might be one of the main reasons of low yields and responsible of the large yield differences between treatments. The control treatments and the off-set treatment (no clay) had over 60% frost induced sterility. Even though increasing amounts of subsoil clay significantly reduced FIS (Figure 3c), the treatments with no incorporation or with incorporation by off-set discs still recorded FIS values above 50%. Spading was the most effective treatment to significantly reduce frost damage to below 40%, regardless of the presence or not of subsoil clay (Figure 3a and b).
Spading was the most successful treatment in this first year of the trial at Yanda. Most importantly, spading was able to produce the highest yields and significantly reduce the frost damage regardless of the addition subsoil clay. This was particularly evident when estimating the simple return of investments on the first year of the trial (ROI= ($/ha gain – $/ha total direct costs) / $/ha total direct costs), based on the mean values presented in Table 3. Because of the high crop-specific costs with barley at Yanda (500 $/ha) and the yield reduction due to frost, spading alone at standard speed was the only treatment that gave a positive ROI on the first year (+0.4 $/ha) followed by negative ROI with spading at ½ speed (-0.18 $/ha) and the control (-0.35 $/ha). These estimates are indicative only, as indirect costs and interests on the initial capital investment are not included in the calculations. For more accurate estimates of ROI, yield results from multiple seasons and crops will be collected in the next 3 years.
|Lead research organisation||
Department of Agriculture and Food WA
|Host research organisation||
West Midlands Group
|Trial funding source||GRDC DAW00244|
|Trial funding source||DAFWA|
This research is funded by DAFWA and GRDC through DAW00244 soil water repellency project, part of GRDC’s Soil Constraints West portfolio of projects. Thanks to Graham White and Jonathan Lampp (Lawson Grains) for clay spreading, undertaking tillage treatments and provision of trial site. Thanks also to Joanne Walker, Chad Reynolds and Larry Prosser (DAFWA) for technical support. Thanks to Ben Biddulph and the frost project for the frost damage analysis.
|Other trial partners||Not specified|
|Trial design||Blocked, randomised and replicated|
Nufab multi-spreader, Agrowplow deep ripper, Farmax rotary spader, Offset disc, digger (clay pit excavation and clay spreader loading).
|Sow date||16 May 2016|
|Harvest date||Not specified|
|Plot size||17m x 18m (trial size 264m x 108m)|
SILO weather estimates sourced from https://www.longpaddock.qld.gov.au/silo/
Jeffrey, S.J., Carter, J.O., Moodie, K.B. and Beswick, A.R. (2001). Using spatial interpolation to construct a comprehensive archive of Australian climate data , Environmental Modelling and Software, Vol 16/4, pp 309-330. DOI: 10.1016/S1364-8152(01)00008-1.