Unlocking the value of strip and disc systems

Unlocking the value of strip and disc systems

Take home messages

  • In the first season of evaluating the use of stripper fronts with low and medium height draper fronts in low rainfall systems, there were moderate summer rainfall events at two sites (Cleve and Minnipa) for potential soil moisture conservation.
  • At Cleve, in a red sandy loam soil, the trial showed stubble from the low height draper front had the lowest average probe-measured soil moisture, followed by high stripper stubble height and medium draper stubble.
  • There was an interaction between stubble height and depth at which the soil moisture was measured but the greatest loss of soil moisture was in the 0-10 cm depth in both locations and soil types.
  • At both Cleve and Minnipa in the stubble and summer weed control trial, having no summer weed control significantly lowered the average soil moisture compared to the sprayed treatments, independent of stubble height.

Background

In 2023, Eyre Peninsula (EP) growers identified the need to better understand the benefits and issues of the strip and disc system in low rainfall environments as a research priority. Growers would like to better understand the components of managing their cropping system prior to transitioning from a draper and tyne system to a strip and disc system. In the first season of research, measurements were taken in low rainfall environments to evaluate if stripper stubble and disc seeding systems;

  • reduce evaporation and contribute to any growth or yield improvement in marginal years with summer and early autumn fallow rain.
  • potentially minimise soil disturbance to conserve more soil moisture at seeding.
  • improve seeding and harvest logistics, particularly speed of operations.
  • potentially improve grain yield in water limited seasons.

Some of the challenges of the strip and disc system include the impact of high stubble load on summer spray efficacy and pest populations (such as snails, mice, and weeds), justifying the financial return on investment (ROI) for machinery changes and understanding herbicide options for disc systems in the absence of soil throw. A grower workshop was held on the 15 February 2024 at Minnipa on ‘Implementing strip and disc systems – tips and tactics for set up, seeding strategies, herbicide control and pest management’ and this workshop helped to co-design the research trials in this study and determine priorities for research in this area.

Method

In November 2023, three replicated broadacre stubble management treatments (stripper stubble [full height], medium height draper stubble and low height draper stubble) were implemented using growers’ harvester fronts at Cleve and Minnipa. The Cleve soil type is a red sandy loam, and the Minnipa site was implemented on a sand to capture differences in soil moisture with 0-30 cm soil moisture probes.

Stubble treatments were implemented at the Cleve site on 17 November 2023. and at Minnipa on 21 November 2023. Stubble height treatments for each site are detailed in Table 1.

Table 1. Summary of treatments at Cleve and Minnipa sites.

Treatment [Height of stubble]Average height of stubble (cm)
Cleve siteMinnipa site
Stripper stubble [full]5570
Draper medium stubble [medium]2538
Draper low stubble [low]1523

Rainfall, humidity and soil moisture were measured at both sites. Sentek Drill & Drop Bluetooth soil moisture probes were placed within the stubble systems to measure at 10 cm intervals to 30 cm soil depth. Gravimetric soil moisture (0 - 100 cm) was also manually measured at both sites, with soil nitrogen levels also being tested.

Soil moisture probes were placed in Plots 1-6 of each strip trial to measure soil temperature and moisture from December 2023 to May 2024. This placement ensured two probe readings per stubble type. At Cleve, readings were taken every half hour until a certain point during 25/01/2024, after which they were taken at two-hour intervals as this was deemed sufficient to detect and track changes over a six week period after a rain event. Similarly, at Minnipa, readings were taken every half hour until a point in 29/01/2024, after which they were taken every two hours. In addition to soil probes, above-ground temperature loggers (TinyTag) were placed in the same plots to record air temperature at stubble level.

Generalised Linear Mixed effects Models (GLMM) were fit to the data for inference and prediction. Models were fit with GLMMTMB (Brooks et al. 2017) or ASREML-R (Butler et al. 2017) depending on the distributional family required. Model fit, presence of outliers and adherence to statistical assumptions were checked by diagnostic residual and quantile-quantile plots. Model performance was further assessed using the Bayesian Information Criterion (BIC) to identify the model with the best balance between fit and complexity. Significance of fixed effects was tested by performing sequential chi-square Wald tests on the models. Response predictions were calculated by computing the estimated marginal mean for the respective treatment and a 95% confidence interval.

A replicated trial to assess the impact of stubble on summer spray efficacy was also implemented across the three stubble systems at both sites (Table 2). These trials measured the effect of weed management on soil water losses over summer. Herbicides were applied at 80 or 120 L/ha water rates, either early in the morning with a low delta T or at mid-day with a high delta T, and a Nil and total weed control treatment which was sprayed twice over summer.  The six herbicide treatments were replicated nine times at each site. Spray cards were used to capture herbicide coverage (% spray card coverage) in the different stubble systems at the initial application. Gravimetric soil moisture (0-100 cm) was manually measured at both sites.

Table 2. Stubble height and summer spray trialat Cleve (17 November) and Minnipa (5 January 2024) with different stubble heights, water rate and Delta T.

SiteCleveMinnipa
Water rate (L/ha)Delta TDelta T value (oC)Delta T value (oC)
80Low3.33.4
120Low4.44.5
80Higher5.611
120Higher5.712

The grower herbicide mix used at Cleve was Glyphosate 1.2 L/ha, Garlon 80 mL/ha, Hammer 80 mL/ha, SOA 1 kg/100 L and LI700 wetter, applied on 20 December, 2023. The herbicide mix at Minnipa was Glyphosate 1.5 L/ha, Garlon 120 ml/ha, SOA 1 kg/100 L and wetter which was applied on 5 January 2024. The main weeds were volunteer cereals from the previous crop and heliotrope, and milk thistle at the Cleve site also.

Results and discussion

Impact of stubble management and soil moisture

To investigate the benefits of summer or early autumn rainfall and the potential trade-offs between the implemented stubble systems, two trials were run at Cleve and Minnipa, South Australia. Cleve had an average stubble load of 3.5 t/ha in November, and the Minnipa sand averaged 2.1 t/ha. There were adequate summer and autumn rainfall events to measure potential benefits of the implemented systems with the rainfall per month for the period of monitoring listed in Table 3. The soil moisture and temperature data analysed for soil moisture retention under the different stubble systems was from December 2023 to March 2024.

Table 3. Monthly summer rainfall (mm) at Cleve and Minnipa for November 2023 to March 2024.

Rainfall (mm)CleveMinnipa
November2946
December9621
January1923
February 02
March112
Total rainfall Nov-March (mm)145104

Figure 1

Figure 1. Soil Moisture Probe Predictions of a) Cleve and b) Minnipa with different stubble type and soil depth (cm).

In the Cleve stubble trial, the low draper stubble corresponded to the lowest average probe-measured soil moisture, followed by high stripper and medium draper stubble. Since there was an interaction between stubble and soil depth, the effect of stubble choice was different depending on the depth of measurement (Figure 1). The greatest loss of soil moisture was in the 0-10 cm depth in both locations regardless of front type. The stubble and spray trial at Cleve showed no significant stubble effect for gravimetric soil moisture across all treatments.

The Minnipa stubble trial in a sand, stripper stubble had the lowest average probe-measured soil moisture, however the size of the differences between different stubble types was minimal. There was similarly a stubble and depth interaction. The strip and spray trials again showed no significant stubble effect for gravimetric soil moisture.

Impact of stubble height and summer spray on soil moisture and weed control

At both the Cleve and Minnipa sites there were soil moisture differences between the spray treatments with the Nil Control plots having significantly lower average soil moisture than other treatments. Average moisture differences between the other spray regimes were much smaller, with Total Control always corresponding to the highest measured soil moisture content, reinforcing the importance of summer weed control. The stubble height by spray treatment interaction was non-significant, meaning that the effect of spray was independent of stubble height.

Weed control differences measured between stubbles and spray treatments at Minnipa included the proportion of dead weeds to total weeds (% weed kill) (Figure 2). Stubble height did not have a significant effect on weed presence. On the other hand, there were large differences in the efficacy of weed control between the Nil Control (no weed kill) and Total Control spray treatments (99% weed kill), which corresponded to the lowest and levels of weed control respectively. High delta T (mid-day application) spray treatments were also found to have lower efficacy (73%) than low delta T (early morning application) treatments (93%).

Figure 2

Figure 2. Weed control (% weed kill) between spray treatments at Minnipa 2024.

Spray penetration was measured using spray coverage cards and the stubble and spray main effects were found to be significant at both locations. At Cleve, the interaction was significant while at Minnipa it was not. Coverage was found to increase from stripper to medium draper to low draper stubble. Also found was that 80 L/ha lower water spraying rates and high delta T admitted less coverage compared to higher spray rate (120 L/ha) and low delta T treatments respectively, on average. In higher stubble situations growers may need to increase water rates and spray in lower delta T conditions to improve weed control.

Conclusion

In the first season of evaluating stripper stubble systems with medium and low draper stubble systems in low rainfall systems, there was reasonable summer rainfall events at both sites meaning there was an opportunity to evaluate the harvest system’s abilities to conserve soil moisture.  The broadacre stubble trial in a red sandy loam soil at Cleve showed the low draper stubble had the lowest average probe-measured soil moisture, followed by high stripper and medium draper stubble. There was an interaction between stubble height and depth with the greatest loss of soil moisture was in the 0-10 cm depth, independent of location and soil types. The Minnipa stubble trial in a sand, stripper stubble had the lowest average probe-measured soil moisture, however, the size of the differences between different stubble types was minimal. There was also a stubble and depth interaction.

At both the Cleve and Minnipa sites there were soil moisture differences between the spray treatments with the Nil Control having significantly lower average soil moisture than other plots. Average soil moisture differences between the other spray regimes were much smaller, with Total Control always corresponding to the highest measured soil moisture content. The stubble and spray interaction was non-significant, meaning that the effect of spray was independent of stubble choice.

Acknowledgements

The research undertaken as part of this project was made possible by the significant contributions of growers through both trial cooperation and the support of the GRDC, the author would like to thank them for their continued support. Thank you to the growers, Paul Bammann, Gareth Scholz, Kelvin Tiller, Michael Brougham and families, and the SARDI Minnipa Agricultural Centre staff Kym Zeppel, Craig Standley, Ian Richter, Katrina Brands, Marina Mudge and Rebbecca Tomney for their help to undertake the site sampling and monitoring.

Contact details

Amanda Cook
SARDI Minnipa Agricultural Centre
226 McKenzie Road Minnipa SA 5654
Phone: 08 8680 6211 Mobile: 0427 270 154
Email: amanda.cook@sa.gov.au

GRDC Project Code: UOA2303-013RTX,