Underperforming sandy soils – targeting constraints for cost effective amelioration

Take home messages

  • Know the water limited yield potential and target the soil constraints to crop water-use: Assessing the yield gap relative to expected gains and seasonal risks, alongside identifying the key soil constraints, are important in developing an amelioration plan with cost effective outcomes.
  • Yield responses to physical disruption are common but not guaranteed: Considering the depth and severity of compaction, any co-occurring constraints, and machinery specific impacts on soil strength offer an opportunity to optimise decisions for cost effective outcomes.
  • Yield responses to increasing fertility at depth (i.e. deep placement/incorporation) are highly dependent on seasonal conditions with risks of neutral or negative yield responses in dry years. Depth of placement and form of nutrition (fertiliser, chicken litter, plant biomass) offer potential to manage nutrient carryover and crop growth responses over multiple years.
  • Long term effects are essential for cost effective amelioration outcomes. Economic analysis of long-term trials (five years) has highlighted the importance of seasonal and crop sequence response effects on the cost benefit outcomes.

Background

Crop water use and productivity on sandy soils are commonly limited by a range of co-occurring soil constraints that limit root growth. Constraints include non-wetting behaviour and poor crop establishment; soil pH issues associated with acidity or alkalinity; a low ability to supply and retain nutrients; a natural tendency to compact or form hard-setting layers, and in some cases, subsoil sodicity and/or toxicities. There are opportunities to improve crop water use through optimising annual and low cost mitigation practices (e.g. seeding strategies, wetting agents, fertiliser placement) or through investing in more intensive and expensive soil profile amelioration approaches (deep ripping, spading, deep ploughing). In the low to medium rainfall zone of the Southern Region, it is important to consider the yield potential boundaries, seasonal risks, and the specific co-occurring constraints when developing an amelioration plan. The GRDC Sandy Soils Program (CSP00203) aims to improve the diagnosis and management of underperforming sandy soil in the Southern Region.

Research activities include:

  • Understanding the potential for yield gains through improved estimates of the yield gap and associated physical, chemical and biological constraints in sandy soils across the region.
  • Monitoring a range of existing long-term trials to assess the five-year impact of a range of amelioration strategies (ripping, spading) with/without amendments (clay, fertiliser, manure, crop biomass).
  • Evaluating amelioration and mitigation approaches to improve crop water use and productivity where physical and nutritional constraints dominate, and where these co-occur with water repellence and/or acidity.
  • Optimising amelioration approaches through understanding how machinery set-up can influence the impact on the soil profile, and strategies to manage seeding depth control and minimise erosion (e.g. one-pass spader-seeding).
  • Assessing cost-benefit outcomes of a range of treatments through economic and risk analysis, and supporting decision making by prioritising the underlying soil constraints.

Methods

Characterisation of soil constraints

A range of physical, chemical and biological analyses have been conducted at core research trial sites to evaluate and describe the soil constraints present, the plant available water capacity, and improve our estimates of the yield gap in sandy soils of the Southern Region.


Research trials

Core project trials across the Southern Region include four long term amelioration sites (established 2014/2015), and seven new research sites (established 2017/2018) that include mitigation and amelioration treatments. Experimental details of the long term PIRSA spading trials and Trengove ripping trial (Trengove and Sherriff, 2018) have been described previously. These trial sites (Karoonda, Brimpton Lake, Cadgee and Bute) have been monitored for 4-5 years for ongoing yield effects, allowing the assessment of the percentage return on investment (marginal return/total costs*100) for a range of amelioration strategies.

New experiments targeted the dominant soil constraints evident at sites – physical and nutritional constraints alone (Waikerie, Carwarp, Bute, Ouyen) or in combination with water-repellence (Murlong, Lameroo) or acidity (Yenda). A summary of amelioration, amendment and placement treatments is provided in Table 1.

Amelioration experiments established in 2018 at Waikerie, Carwarp and Bute aim to evaluate whether increasing amelioration depth and/or nutrient supply within the profile results in cost effective outcomes. The Ouyen trial established in 2017 aims to evaluate the incorporation of farm grown biomasses (vetch hay, oaten hay), with comparison to other amendments (chicken litter, complex carbon compost) on profile nutrition, crop productivity, and the nitrogen (N) balance over multiple years (Moodie and Macdonald, 2018).

Addressing the management of severe water repellence, the 2018 Murlong site includes contrasting amelioration approaches (spading versus topsoil slotting i.e. inclusion plates ± N-rich biomass) alongside mitigation strategies evaluating wetting agent type and placement and furrow management. With acidity a common issue in NSW sandy soils, the Yenda amelioration experiment aims to evaluate deep ‘sweep’ cultivation (30cm) with/without amendments (urea, lime, 3-9t/ha chicken litter) to shatter and ameliorate a hostile layer approximately 15cm deep (Haskins et al., 2018).

Table 1. Summary of project amelioration trialsindicating the type of physical amelioration approach, amendments used and placement strategy.

Site (Yr Est)

Physical amelioration* and depth (cm)

Amendment type#

Placement^

Waikerie (2018)

Rip 30, Rip 60

Chicken litter (2.5t/ha); fertiliser matched

deep, surface

Carwarp (2018)

Spaded 30, Rip 30,
Rip 60

High-N biomass (6t/ha)

deep

Bute (2018)

Rip 30, Rip 50, TSSlot 50

Chicken litter (2.5-7.5t/ha)

deep, surface

Ouyen (2017)

Spaded 30, Rip 30

Crop biomasses (6t/ha), chicken litter, compost, fertiliser matched

incorporated, deep

Murlong (2018)

Spaded 30, TTSlot 30, TTSlot 40

High-N biomass (5t/ha); fertiliser

incorporated

Yenda (2017)

Sweep 30, Rip 30

Chicken litter (3-9t/ha)

incorporated

* including ripping (Rip), spading (Spade), topsoil slotting (TSSlot: ripping with inclusions plates), and sweep-cultivation (Sweep), with depth (cm) indicated. # amendments used vary depending on regional availability, where chicken litter is considered unavailable in the VIC Mallee and Eyre Peninsula. ^ placement of amendments includes ‘surface’ applied (no intervention), ‘incorporated’ through Spade and/or TSSlot, or actively placed at a controlled rate at the specified target depth.

Results and discussion

Know the potential and target constraints to crop water use

Estimates of the yield gap across sandy soil sites in the Southern Region vary from 2-3t/ha where growing season (GS) rainfall is less than 300mm (Table 2). The yield gap is based on an estimate of the yield potential for wheat in an average season minus the current attainable yield based on grower data. The estimated yield gap provides important information when developing an amelioration plan, helping to highlight the limits of productivity within the context of rainfall, and local knowledge of gains that can be achieved through annual strategies (e.g. fertiliser management, change in crop sequence). Further characterisation will refine the yield gap estimates taking into account the plant available water capacity measured at trial sites.

The selected trial sites reflect the prevalence of water repellence in the sands of SA, with lower occurrence of this constraint in Victorian and NSW Mallee soils (Table 2). Measurements of soil strength indicate that moderate constraints to root growth (1.5-2.5 MPa) are reached within 20cm, and severe physical constraints (2.5-3.5 MPa) are common within 30cm (Table 2), with examples of the variation in soil strength with depth shown in Figure 1. Nutrients commonly identified as marginal in the top 30cm included N, phosphorus (P), zinc (Zn), copper (Cu) and manganese (Mn).

Table 2. Characteristics of Sandy Soils Experimental Sites;including estimates of the potential yield, current attainable yield and the yield gaps for an average growing season (GS, April-October). Rating of water repellence (top 5cm, based on molar ethanol drop) and soil strength (top 30cm, based on penetration resistance).

Site

Estimated Yields

Select constraint ratings

Location

GS Rain (mm)

Potential Yield

(t/ha)

Current attainable Yield

Yield Gap (t/ha)

Repellence

Soil strength (30cm)

Waikerie

157

2.9

1.0

1.9

Low

Severe

Carwarp

174

3.5

1.0

2.5

0

Severe

Ouyen

213

4.5

1.5

3

0

Severe

Karoonda

235

5

1.5

3.5

Moderate

Moderate

Murlong

251

5.2

1.5

3.7

Severe

TBD

Yenda

252

5.8

2.5

3.3

0

Severe

Lameroo

270

5.9

2.5

3.4

Moderate

Moderate

Bute

298

6.5

3.5

3

Low

Moderate

Brimpton

377

8.3

3.0

5.3

Moderate

TBD

Cadgee

410

9.5

1.3

8.2

Severe

TBD

* Potential Yield = ((0.25 x fallow rainfall)+ GSR – 60)*22*1.12. Repellence rating is based on molar ethanol drop (MED) testing of 0-5cm and 5-10cm soil samples. Soil strength rating is based on assessing penetration resistance within the top 30cm, where 1.5-2.5 MPa = moderate, 2.5-3.5 = strong, and >3.5 = severe.

Figure 1. Examples of the variation in severity and depth of penetration resistance (MPa)in a range of sandy soil trial sites across the Southern Region. The black line indicates the site average, with grey shading indicating minimum and maximum readings across six measurements. Soil strength 1.5-2.5 MPa = moderate, 2.5-3.5 = strong, and >3.5 = severe.

Monitoring long term amelioration trials


PIRSA long term trials on water repellent sands that have physical and nutritional constraints (Karoonda, Brimpton Lake) or acidity and nutritional constraints (Cadgee) have been monitored for five years. Cumulative yield gains across three cereal years (Table 3) demonstrate that yield gains at Karoonda and Brimpton Lake have been responsive to spading (approx. +2t/haat both sites). Incorporation of N-rich crop biomass (10t/ha lucerne) has resulted in 1.3-1.6t/ha, and largely accounted for in the first two years. Yield gains from clay incorporation were only evident at Cadgee (+1.8t/ha), which had little response to spading, but a positive and continuing response to N-rich biomass (+1.6t/ha). The lack of strong physical constraint and the presence of acidity at Cadgee are likely drivers of the different responses.

Table 3. Cumulative cereal yields (2014, 2015, 2017) across PIRSA long term amelioration trial.

Cumulative Yields (3 years, t/ha)

 

Karoonda

Brimpton Lake

Cadgee

Unmodified

2.17

4.36

3.21

Spading

4.13

6.58

2.82

Spading +lucerne

5.39

8.15

4.83

Spaded clay

4.14

7.49

4.62

Lucerne =10t/ha

These long-term experiments have demonstrated lasting responses to spading across three sites, broadly similar gains to the incorporation of lucerne, and site/seasonal responses to clay. A new experiment at Murlong builds on these results to evaluate the potential of topsoil slotting compared to spading, as a lower risk approach to address repellence (severe), compaction and nutritional constraints. The new experiment is co-located with a mitigation experiment evaluating wetter chemistry and placement. Comparing annual lower cost strategies against higher cost amelioration will be important in developing a framework to support grower decisions for cost effective outcomes on repellent sandy soils.

Yield responses to physical disruption and increasing profile fertility


A wide range of experiments have demonstrated that physical interventions (ripping, spading, deep cultivation) can improve crop productivity in compacted sandy soils (for example, Trengove et al. 2018; Moodie and Macdonald, 2018). The extent of the opportunity to further increase yield gains for effective cost benefits through incorporating amendments (fertilisers, manure, crop biomass) is less well understood. Depth of placement and type of amendment influence the rooting depth, the timing of nutrient supply, and access to profile moisture. These factors influence the balance of crop growth, development, and grain filling. A series of experiments across the southern rainfall range have been established to address these questions in deep compacted sands with nutritional limitations (Waikerie, Carwarp, Bute, Ouyen).

Targeting the depth of amelioration to compaction thresholds (with/without deep placement of amendments), three new trials (2018) demonstrate a range of site-specific responses (Figure 2). The potential for yield gains at Waikerie was limited by available water (95mm GS rainfall), with small yield gains under 60cm ripping treatments (+0.26t/ha) and no significant response to deep placed nutrition.

At Carwarp (approximately 70mm GS rainfall), the yield responses to a range of amelioration approaches (ripping, spading) were relatively consistent (+0.5t/ha) and unaffected by depth, despite evidence of deeper crop water use. Increasing profile nutrition through incorporation of N-rich biomass had either no benefit (deep placed) or a negative yield effect (spading) associated with high early biomass production.

In contrast to the dominance of physical effects at Waikerie and Carwarp, crop yields at Bute were more responsive to improved nutrition (7.5t/ha surface chicken litter), demonstrating yield gains of approx. 0.9t/ha compared to an average gain of 0.29t/ha from physical interventions alone. The Bute site had the lowest severity and depth of physical constraint across project sites (Figure 1). All trials will continue for a further two years to evaluate the longevity of physical and nutrient carry-over effects.

Figure 2. Cereal yields across three amelioration trial sites including non-ameliorated control, ripped (Rip30, Rip50, Rip60), spaded (Spade30), or topsoil slotted (TSSlot30) treatments, and where numbers indicate depth (cm) of intervention. Grey bars represent yields under control fertiliser inputs, while black bars indicate gains/losses under nutrient enriched treatments. Letters indicate significant amelioration impacts within sites (n=4), noting broken y-axis to account for higher yields.

Established in 2017, a trial at Ouyen is evaluating the incorporation (spading) of farm grown biomasses (vetch hay, oaten hay). It includes other amendments to allow regional comparisons (chicken litter) and assess longevity compared to complex/stable carbon inputs (compost). In the first-year spading suffered an establishment penalty (110 vs. 60 plants/m2), resulting from sub-optimal seeding depth control, with spaded yields tending to only have a small benefit (+0.4t/ha) compared to the control (1.3t/ha). The two-year cumulative gain from spading alone was 0.58t/ha. Incorporation of N-rich amendments (vetch, chicken litter, compost) supported higher yields over both years (2.9-3.5t/ha cumulative totals), representing gains of 0.85-1.73t/ha over and above the spaded control. Where high fertiliser additions (156kg N/ha, matching vetch N input) were incorporated through spading, yields were comparable but far more variable between replicates. Measurement of the rates of microbial decomposition and changes in soil N pools (mineral N, microbial biomass N and dissolved organic N) indicate differences in nutrient cycling between treatments that will be monitored over time.

Figure 3. Cereal yields in response to spading and amendment incorporation at Ouyen, Victoria.Yields include two consecutive years following establishment in 2017; significant within year differences from the unspaded (Nil) control are indicated (*). Treatments include an undisturbed (Nil) control, and spaded treatments with no additional inputs (control), urea, three hays including vetch, oaten hay and a mixture of the two (C:N ratio indicated), chicken litter, and compost.

Conclusions

There are substantial opportunities to increase yield on underperforming sandy soil in the Southern Region. However, it is important to consider the current yield gap, the expected yield gains, and the seasonal risks within the low to medium rainfall environment. Identifying the key soil constraints limiting crop root growth and water extraction is central to developing a targeted and cost-effective amelioration plan.

Across the Southern Region, compaction and yield responses to physical disruption are common but not guaranteed. Considering the depth and severity of compaction and the co-occurring soil constraints is important. Opportunities to optimise physical amelioration include understanding machinery specific impacts on soil strength and mixing ability and improving seeding depth control for even crop establishment. Experiments aiming to increase yields through incorporating or deep placing fertilisers or organic amendments demonstrate high seasonal variability, with risks of neutral or negative yield responses in dry years. Understanding the impact of placement depth and amendment form on the timing of nutrient supply and water use is required to harness any additional potential above physical intervention alone. Interactions with site, season and/or crop sequence have been demonstrated and highlight the need to better understand post-amelioration agronomy.

Useful resources and references

PIRSA GRDC Sandy soils (CSP00203) site results summary.

Trengove, S and Sherriff, S (2018). Amelioration of sandy soils - Opportunities for long term improvement, GRDC Grains Research Update, Adelaide 2018. (https://grdc.com.au/resources-and-publications/grdc-update-papers/tab-content/grdc-update-papers/2018/02/amelioration-of-sandy-soils-opportunities-for-long-term-improvement)

Moodie, M. and Macdonald, L. (2017). Increasing water extraction and production on Mallee sands through enhanced nutrient supply in the root zone. MSF Research Compendium 2017. (http://www.msfp.org.au/increasing-water-extraction-production-mallee-sands-enhanced-nutrient-supply-root-zone)

Desbiolles, J., McBeath, T., Macdonald, L., Llewelly, R., Davoren, B. and Shoobridge, W. (2017). Testing the concept of fertility strips to increase productivity on deep sands. MSF Research Compendium 2017. (http://www.msfp.org.au/testing-concept-fertility-strips-increase-productivity-deep-sand)

Haskins, B., Whitworth, R., Kookana, R., and Macdonald, L. Increasing productivity on low fertility (sandy) soils. GRDC Update, Wagga Wagga 2018. (https://grdc.com.au/resources-and-publications/grdc-update-papers/tab-content/grdc-update-papers/2018/02/improving-productivity-on-low-fertility-sandy-soils)

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. CSP00203 gratefully acknowledges industry collaboration including Groocock Soil Improvement, Peatsoils, Neutrog, and Moodie Agronomy. Murray Unkovich is thanked for valuable discussions and contributions.

Contact details

Lynne M Macdonald
PMB 2, Glen Osmond, SA 5064
08 8273 8111
lynne.macdonald@csiro.au
@Soil_Mac

GRDC Project code: CSP00203