- Trial Rationale
- Steps Taken
- Lessons Learnt
- Looking Forward
Sandy soils with a clay content of less than 5% are the most susceptible to water repellency resulting in poor germination of crops and pastures. This leaves the topsoil vulnerable to water and wind erosion (Harper and Gilkes 1994). Other impacts of non-wetting soils are low yielding crops, higher weed densities, increased herbicide resistance and inefficient nutrient use in crop and pasture systems (Hunt and Gilkes 1992).
Non-wetting properties predominantly affect the surface (0-10 cm) of the soil. Options to address this constraint include:
- Inverting the top soil with mouldboard plough;
- Deep mixing with rotary spading;
- Applying chemical wetting agents at seeding; and
- Placing seeds deep into the soil underneath the topsoil layer, knifepoint.
Corrigin Farm Improvement Group (CFIG) is well aware that non-wetting soils are a major issue for many of their members, in response they sought to trial methods for growers to cost effectively reduce water repellence.
In this trial, five treatment options for non-wetting soils were used, including the mechanical and chemical alternatives described above.
The site chosen was the paddock ‘Bell Rock Soak’ (BRS), owned by Tony Guinness and shown in Figure 1. It had been used to grow mace wheat in 2014 with an average yield of 3 t/ha followed with a clover based pasture in 2015. The paddock was limed at a rate of 1 t/ha in 2011.
Five wetting treatments and a control were tested in plots including:
- Chamberlain one way disc plough inverted non-wetting topsoil to a depth of about 35 cm;
- Spader with a working depth of 28 – 35 cm. Rotating spades buried the topsoil while lifting the subsoil. About two-thirds of the topsoil was buried below 10 cm;
- DBS knifepoint (Figure 2) with a ripping depth of 70 mm (Control) and seed deposited at 10 mm;
- DBS knifepoint with a ripping depth of 90 mm and seed deposited at 20 mm;
- Wetting agent – Bi-Agra Band as per manufacturer’s instructions; and
- Wetting agent – SE14 as per manufacturer’s instructions.
Two soil samples were taken from the BRS paddock in April 2016 prior to spraying and sowing mace wheat in May. Test results indicated pH levels at the site were good, while nitrogen was low due to poor clover growth and depletion from the previous wheat crop. Phosphorus and organic carbon levels were also low. Additional nitrogen was applied at seeding at the recommended rate of 80 kg/ha K-Till Extra, 50 L/ha Flexi N post emergent and Flexi N 30 L/ha at tillering.
The plots were then seeded using the different chemical and mechanical treatments described. Plant establishment counts were taken in June after seeding and wheat yield and quality data were collected at harvest.
Tony anticipated that soil moisture (alleviated by treatments) would be the limiting factor rather than nutrients, however, the 2016 growing season produced a wetter start than 2014 contributing to increased emergence on top of the 5 treatments employed.
Plant establishment counts found that all treatments had similar results. By harvest, the spaded plot had the highest wheat yield of 3.7 t/ha (Table 1).
Both soil incorporation treatments (spader and one way disc plow) yielded higher than the inclusion of wetters or the knifepoint to a depth of 90 mm. There was only a 95 kg difference in yields between the two plots with wetting agents (Bi-Agra Band 2.9 t/ha and SE14 2.8 t/ha).
The difference between the highest (spader) and lowest treatment (DBS knifepoint 90 mm) yields was 890 kg/ha.
Return on Investment
The control and incorporated plots were the most profitable treatments and the spader treatment had the second highest gross return despite the much higher input costs.
In a season such as 2016, where sufficient rainfall arrived early in the season for plant establishment and growth, soil wetting agents are probably not required, which would reduce input costs.
All the treatments made a profit in 2016 of between $303.1/ha and $443.6/ha as shown in Table 2.
All treatment types led to significant yield increases on those experienced in 2014 under traditional management. Unfortunately, from a demonstration perspective, the wet start to 2016 caused higher than usual water infiltration that significantly advantaged early crop establishment. This made it difficult to clearly link treatments to the significant yield increases experienced.
The 2017 season, however provided a drier year and Tony said the response of plants to wetting treatments was still good a year later.
In order to be conclusive, the demonstration would need to be replicated in year with similar rainfall to 2014. Nevertheless, Tony has been sufficiently encouraged by the results (both in terms of yield and gross return) to continue to experiment on his own.
Additionally Tony would also like to compare each treatment with twinpoints to see if there is a difference between knifepoints and twinpoints for ongoing seeding.
- Land Manager
- Tony Guinness
- NRM Region:
- Average Rainfall:
- Medium - 325-450mm
- Enterprise Mix:
- System Constraints:
- High weed burden, Non-wetting Soils, Soil Acidity
- Corrigin Farm Improvement Group, Sellars Agricultural Services (Technical Advisor), Wheatbelt NRM