Improving crop production outcomes on repellent sands

Take home messages

• Crop production can be improved in repellent sands using amelioration (deep tillage and amendments) or modified sowing techniques.
• Recent improvements for the set up and implementation of inclusion ripping have seen results that are at least equal to that of spading.
• Sowing based strategies can be a useful alternative for growers not choosing to ameliorate.

Background

Water repellency occurs in sandy soils through the coating of sand particles from waxy material derived from degrading plant material. There are more than 3 million ha of sands in the southern cropping region of Australia and almost 20% of the cropping area in this region is affected by repellency (Unkovich et al. 2020). Repellency can limit on-farm productivity through erosion, poor water infiltration and water holding, poor crop establishment and the related issues of weed and disease proliferation. Many of these sands also have high soil strength (measured as penetration resistance) which restricts the growth and resource use of crop roots. The sandy soils project has examined a range of amelioration (deep tillage and amendments) and mitigation (crop row position, wetters, seeding inputs) treatments to reduce or overcome the effects of repellency and high strength in sandy landscapes. More recent Future Drought Fund and GRDC investments are examining strategies that improve crop establishment for wheat, pulses and canola, which are relevant to repellent sands.

Recent surveys of growers in southern region landscapes indicate that 50% of growers have ameliorated some sand in the last 5 years and they plan to double the amount of ameliorated sand in the next 5 years. There is recognition across the industry that understanding the constraints, how to best tackle those constraints from an engineering perspective and how to integrate them into whole-farm management is critical to widespread adoption of amelioration techniques.

The aim of the Sandy Soils project is to increase crop productivity in underperforming sandy soils in the southern cropping region by improving the diagnosis and management of constraints. Many of the outcomes from that project are presented below but growers are still experiencing mixed success after implementing amelioration and/or mitigation strategies in repellent sands. This paper focuses on those strategies that have been the most reliable at improving production on repellent sands of the southern region and draws on some specific examples from sites in the southern Mallee region of South Australia.

Method

Constraint identification

The key measurements for constraint identification are water repellence (water drop penetration test or molarity of ethanol droplet test), soil strength (penetration resistance or bulk density), pH, and soil and plant nutritional status. Practical approaches to assessing these constraints on-farm have been outlined in the factsheets listed under References. We utilised the techniques outlined in our factsheets to categorise the constraints at each of our sites as low, moderate and severe.

Testing amelioration techniques

A range of research experiments were established across the low to medium rainfall environments of the southern region on sites categorised according to their primary soil constraints. Experiments for the research program were established between 2014 and 2019, while a broader validation program ran from 2019 to 2021, including a range of deep ripping (30–60cm deep), spading, inclusion ripping and/or inversion ploughing approaches, with/without amendments (fertiliser, N-rich hay, chicken manure, clay). Practical advice on the set up and implementation of these treatments is outlined in the factsheets listed under References. All experiments monitored the effects of amelioration on crop growth and yield, while the research program had a further set of more detailed soil and crop measurements. In all, there were 32 experimental sites with 105 site years of data. All yield results have been databased and analysed and are available via the SANDBOX App. In this paper, we present yield responses according to machinery treatment (ripping, spading) constraints, but we will also draw from specific responses at a site at Younghusband in the southern Mallee of South Australia.

Younghusband – testing amelioration and sowing techniques to improve crop production on a repellent sand

At Younghusband, amelioration treatments of deep ripping to 60cm depth using narrow straight shank tynes set at 56cm spacing and rotary spading to 30cm depth were evaluated. Additionally, inclusion ripping was also compared where the same ripping tynes were fitted with inclusion plates 39cm high, 60cm long and 13.1cm space width, allowing topsoil material to backfill the inclusion space forced open behind the ripping tyne. The 6-row wide, 50m long plots were sown to wheat on 28cm row spacing in the first year, followed by a barley crop and a lentil crop in years two and three, respectively. A range of seeder-based constraint mitigation techniques were also tested over non-ameliorated plots to manipulate crop productivity in repellent sand. A range of seeding strategies were also tested including on-row sowing and application of wetters to the seeding furrow.

Lowaldie –testing depth of sowing to improve wheat production on a repellent sand

A range of wheat varieties including long coleoptile Mace, standard and long coleoptile Yitpi, along with Scepter (standard for 120 plants/m2 and high for 200 plants/m2 seeding rate) and a vetch reference (cv. Rasina) were direct-sown into wheat stubble at both 5cm and 12cm depth in a repellent sand in dry conditions in late April at Lowaldie in 2022.

Results and discussion

Yield responses to amelioration techniques

Crop responses to amelioration of sandy soils varies according to the severity of the primary constraint. Figure 1A shows the response to ripping over time for soils with moderate or severe physical constraints. While the initial response to ripping is similar for both categories, the cumulative response is greater for sands with a severe physical constraint. Figure 1B shows the response to spading over time for soils with nil through to severe water repellence. The amelioration of repellence relies on the mixing or dilution of repellent surface soil within the spaded profile. Increasing severity of repellency results in greater cumulative yields after spading. The shading in the figure shows the range in responses within each category of constraint, which arises due to seasonal constraints, variation in other soil constraints and post-amelioration management (for example, nutrient input, crop establishment, erosion).

Figure 1. Southern Sandy Soils project cumulative yield responses (as mean in bold line and cv in grey shadow) over time to ripping, and spading (amelioration occurred in year 0). The responses have been separated according to the category of constraint and we present the examples of ripping responses according to categories of soil physical (measured by soil strength) and spading responses according to water repellence (measured by water drop penetration test) constraints.

Younghusband

In this experiment, techniques were tested that could either mitigate the effects of water repellency through modifications at seeding or ameliorate both the water repellency and high soil strength. Inclusion ripping was included as a lower erosion risk option to the full mixing technique of rotary spading. Techniques that thoroughly mix the soil profile and dilute repellency (spading and inclusion ripping) had the largest production effect, with 2-3 times more yield than the inter-row sown control (Figure 2). The sowing strategies offered significant yield benefits in barley, with 0.5 times more yield than the control, but these benefits were not realised in lentils in 2022 (Figure 2). Interestingly, there were some sowing strategy benefits measured in lupins in the same experiment in 2022 (data not shown).

Figure 2. 2021 barley and 2022 lentil grain yield responses to wetter (Bi-Agra and SE14™), on-row sowing, deep ripping at 60cm, deep ripping with inclusion plates to 60cm (Inc Rip 60) and spading to 30cm.

Lowaldie

Deep sowing and high seeding rate (SR) proved to be beneficial for crop establishment (Table 1). There were substantial benefits with respect to both the speed of crop establishment and the number of plants established. These effects translated to a yield benefit for deep sown crops with an average yield (3.1t/ha) 0.2 times greater than shallow sown (2.6t/ha) wheat (P<0.001, data not shown).

Table 1: Final plant establishment numbers at Lowaldie in 2022 with an Lsd of 13 at p=0.05.

Conclusions

There are opportunities to transform crop productivity in repellent sands of the southern region. The substantial yield responses observed demonstrate the adverse effects and opportunity cost of high soil strength and water repellency on grain crop production and that a new, higher yield potential can be achieved on sands in this region with improved management techniques. The success of these strategies at farm level is underpinned by understanding the key constraints in each field, identifying, and optimising the machinery treatment to manage that constraint using seeder-strategies and amelioration techniques.

Acknowledgements

The research undertaken as part of this project is 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. We thank the technical teams who deliver the experimentation for the Sandy Soils Project and Resilient and Robust Groundcover Drought Fund Project. GRDC project CSP00203 research and validation activities are a collaboration between the CSIRO, the University of South Australia, the SA Government Department of Primary Industries and Regions SA, Mallee Sustainable Farming Inc., Frontier Farming Systems, Trengove Consulting, AgGrow Agronomy, AIREP, Soil Function Consulting and MacKillop Farm Management Group.

References

Unkovich M, McBeath T, Llewellyn R, Hall J, Gupta V, Macdonald L (2020) Challenges and opportunities for grain farming on sandy soils of semi-arid south and south-eastern Australia. Soil Research 58, 323-334.

Diagnosing sandy soil constraints: water repellence and pH (south-west) (

Useful resources

Diagnosing sandy soil constraints and water repellance

Diagnosing sandy soil constraints: high soil strength (south-west)

Diagnosing sandy soil constraints: nutrition (south-west)

Inclusion ripping technology: national

Soil mixing by spading: national 

Ripping technology: national

Soil wetter: national fact sheet

Seeding sandy soils: national 

Contact details

Therese McBeath
CSIRO Agriculture and Food
Waite Road, Urrbrae SA 5064
08 8303 8455
therese.mcbeath@csiro.au