Take home messages

• Crops growing on a mildly calcareous soil were less responsive to the strategies investigated than those grown on highly calcareous soils of upper EP.
• Short-term topsoil strategies resulted in better gains in crop biomass and yield when compared to longer-term subsoil strategies.
• A carbon-coated mineral (CCM, formerly bespoke biochar) applied in the topsoil improved crop vigour, biomass and grain yield, as well as providing benefits into the following crop.
• Increasing seeding rates and nutrition at sowing was effective at achieving high plant densities, crop biomass and grain yield.
• High soil strength is an issue in calcareous soils but positive responses to deep ripping are not common and are usually limited by the hostile subsoil.
• In 2021, barley performed better when P fertiliser was banded just below the seed row rather than when P was banded 20cm below the soil surface.
• A delay in P acquisition can cause a decrease in crop yields in a P responsive situation, and there is very little evidence of deep P having superior benefits to the following crop.

Background

Calcareous soils (Calcarosols) are those where calcium carbonate is an important part of the soil composition within at least some layers of the soil profile. Calcarosols occupy about 60% of the cropping soils in south-eastern Australia, and more than 1.1 M ha of South Australian cropping areas are highly calcareous. Within SA, key sub-regions that have a high proportion of highly calcareous soils include upper and western Eyre Peninsula (EP) and lower Yorke Peninsula (YP), while moderately calcareous soils are prevalent in the crop producing areas of central EP, upper YP, the Murray Mallee and the lower South East (SE).

Highly calcareous soils challenge crop production with a range of constraints and this limits the effectiveness of improved agronomic practices. Early crop vigour is poor and crop production continues to be limited to very low nitrogen and water use efficiencies. This collaborative project funded by the CRC for High-Performance Soils and GRDC brought together a multidisciplinary team with expertise in calcareous soils and/or soil constraints to identify constraints and develop strategies to overcome them.

The main aim of this research initiative was to identify and overcome the impacts of topsoil and subsoil conditions of highly calcareous soils on crop production on the upper EP of SA. A holistic approach to addressing these constraints to crop productivity and profitability was implemented. Outcomes of this project focused on the development of management strategies which improve soil condition, increase nutrient and water use efficiency of crops and farm profitability, as well as improved knowledge of the impact of high carbonate on crop performance.

Recent research in Queensland has shown that crops can struggle to access P fertiliser which is placed in or close to seed rows because their soils are frequently dry in that layer. Placing P fertilisers deeper (20–30cm below the surface) with moisture present has improved crop access and crop performance. In southern Australia, although rainfall is more frequent during the growing season, periods of prolonged dry topsoils still occur and many soil profiles in southern Australia have very low P reserves below the cultivated layer, so placing P deeper may be more effective than current strategies of in or around seed rows. GRDC funded a project (‘Maximising the uptake of phosphorus by crops to optimise profit in central and southern NSW, Victoria and South Australia’, DAN2001-033RTX) to investigate the merits of deeper placed P on crop performance.

This paper summarises the results of the soil CRC project code 4.2.003 (GRDC agreement, HPS2006-001OPX), and includes key findings from the GRDC project - DAN2001-033RTX.

Research

Field experiments were conducted from 2020 to 2022 on three sites on the upper EP at Minnipa, Poochera, and Port Kenny. At each site in 2021 and 2022, two replicated field trials were established to investigate amelioration strategies which have potential to overcome soil constraints on poor performing highly calcareous soils, and improve early crop vigour, soil health, crop biomass, and grain yield. Three of the six trials were set up to investigate long-term subsoil strategies by placing different amendments (pelleted chicken manure, CCM, trace elements, granular and fluid fertilisers) at 20cm and 40cm depths. CCM is phosphoric acid activated during its preparation and was sourced from our collaborative research partners – NSW DPI, and Neutrog is pelletised composted chicken manure.  The other three trials investigated short-term topsoil strategies (pre-seeding N, granular and fluid P, trace elements, CCM, fungicide, soil wetter and sweep cultivation). The complete list of the treatments is presented in Table 1.

Subsoil treatments were implemented on 14 May 2021 at Minnipa, on 18 May 2021 at Poochera and on 19 May 2021 at Port Kenny. All but one of the topsoil treatments (Table 1) were intended as annual strategies implemented at sowing. Sweep cultivation was implemented on 15 April 2021 at all sites to simulate a practice common in these districts and as a strategy to reduce Rhizoctonia. The treatment CCM is phosphoric acid activated during its preparation and was sourced from our collaborative research partner NSW DPI.

In 2021, all the trials were sown to Scepter wheat at a standard rate of 60kg/ha and 50kg/ha DAP, and in 2022, all trials were sown to 50kg/ha Maximus barley and 50kg/ha DAP. Plant measurements included crop establishment, crop vigour, early (GS31, stem elongation) and late (GS60, flowering) biomass, root health, plant nutrient analysis at flowering, and grain yield and quality. The experimental design used was a Randomised Complete Block Design with four replicates, and statistical analysis of data was performed using standard ANOVA models in RStudio.

Results

For comprehensive data and full analysis, please refer to articles in Eyre Peninsula Farming Systems Summary 2021 (Dzoma et al. 2021) and 2022 (Dzoma et al. 2021).

Crop establishment and early crop vigour

None of the subsoil strategies investigated improved plant population (plants/m²) at any of the three sites in 2021 and 2022. However, in 2021 when the trials were established, deep ripping with inclusion plates caused a lot of soil disturbance which resulted in a rough and cloddy seedbed, and consequently, the lowest plant densities at all sites. In comparison to typical practice (control), deep ripping with inclusion plates resulted in a 50% (Minnipa), 34% (Port Kenny) and 25% (Poochera) reduction in plant population. Furthermore, deep ripping without inclusion plates reduced plant density by 14% at Port Kenny, 20% at Poochera and 33% at Minnipa compared to the control. In both growing seasons, the use of a higher seeding rate improved plant populations at all sites, but none of the other topsoil strategies significantly improved plant numbers. In 2022, the use of a higher seeding rate increased plant population by 126% at Poochera, 96% at Minnipa and 65% at Port Kenny.

In 2022, subsoil strategies at Minnipa and Port Kenny did not affect early crop vigour. However, at Poochera deep ripping with inclusion plates plus Neutrog improved crop vigour by 30% when compared with typical practice. Fresh CCM @ 500kg/ha consistently improved early plant vigour in topsoil trials at all three sites. There were no early crop vigour assessments in 2021.

Flowering biomass

Subsoil

In both growing seasons, flowering biomass was not affected by any of the subsoil strategies implemented at Minnipa and Poochera, and physical disturbance through deep ripping (with or without inclusion plates) did not improve flowering biomass at any site. However, in 2021 at Port Kenny, plants in plots with deep ripping with CCM (4.5t/ha) or Neutrog (4.3t/ha) had higher flowering biomass than those in the control plots (3.3t/ha), and in 2022 at Port Kenny, deep ripping with Neutrog (with or without inclusion plates) resulted in 30% more biomass than typical practice. Plants in plots with deep ripping with CCM and Neutrog had high cumulative flowering biomass over two growing seasons at Poochera and Port Kenny. Results also suggest a P response at Poochera shown by the extra 3.2t/ha of biomass when phosphoric acid was applied in the subsoil. None of the subsoil strategies implemented at Minnipa performed better than typical practice over the two growing seasons.

Topsoil

In 2021, ‘High_seedrate_fungicide_bandedN_phosacid_TEs’ and‘CCM’consistently yielded more biomass than typical practice. At Port Kenny, high seeding rate increased biomass by 22% compared to typical practice. In 2022, late flowering biomass was affected by numerous isolated Rhizoctonia patches across the Poochera trial, by take-all and crown rot patches at Port Kenny, and by boron toxicity, net form of net blotch and leaf rust at the Minnipa site. Nonetheless, the treatment ‘high_seedrate_fungicide_bandedN_phosacid_TEs’ consistently produced higher flowering biomass than the typical practice at all three sites. Plants in plots treated with fresh and residual CCM applied at 500kg/ha yielded more biomass at Minnipa when compared to typical practice. There was a 20% reduction in late flowering biomass at Poochera from the use of ‘SE14_wetter’ and from the ‘Seed_coating’ when compared to typical practice.

The 2021 applied ‘CCM @ 500kg/ha’and ‘high_seedrate_fungicide_bandedN_phosacid_TEs’strategies resulted in more cumulative flowering biomass in two growing seasons consistently at all three sites. ‘Seed_coating’ and the ‘SE14_wetter’ are the only two topsoil strategies that resulted in reduced biomass at flowering at all three sites over the two growing seasons.

Grain yield

All sites were harvested during November in both years. Higher grains yields were achieved in 2022 compared to 2021.

Subsoil

In 2021, none of the strategies at Minnipa improved grain yield above typical practice (3.51t/ha). Deep ripping with inclusion plates had the lowest yield (2.58t/ha). At Poochera, deep ripping and incorporating 5t/ha of CCM (3.13t/ha) or Neutrog (3.04t/ha) had higher yields than typical practice (2.57t/ha). Deep ripping with inclusion plates and Neutrog, and deep ripping with phosphoric acid and trace elements (Zn, Cu, Mn) also yielded higher than the control. At Port Kenny, deep ripping with inclusion plates and incorporating Neutrog resulted in the highest yield (2.51t/ha). Deep ripping with CCM (2.24t/ha) or with Neutrog (2.26t/ha) also yielded more than the control (1.86t/ha).

In 2022, none of the subsoil treatments changed grain yields at Minnipa, when compared to typical practice. At Poochera, all amendments applied into the subsoil increased yields above typical practice, with CCM (4.41t/ha) and Neutrog (4.28t/ha) being the highest yielding treatments. At Port Kenny, only Neutrog incorporated by inclusion plates yielded higher than typical practice.

Table 1 shows the change in grain yield at all sites over the two growing seasons relative to the cumulative (2021 + 2022) grain yield of the typical practice. Typical practice had the highest cumulative grain yield at Minnipa (7.66t/ha) and all other strategies reduced cumulative yield over the two seasons. At Poochera, ‘DR_CCM’ had the highest cumulative change in grain yield (1.58t/ha) compared to typical practice. ‘DR_Inclusion_plates_Neutrog’ resulted in cumulative changes in grain yield over 15% of typical practice at both Poochera and Port Kenny.

Table 1: Cumulative change in grain yield (t/ha) in the topsoil and subsoil trials, relative to typical practice at Poochera, Minnipa and Port Kenny from 2021 and 2022.

Data for 2021 high seed rate, and 2022 applied CCM at 100kg/ha and 500kg/ha are not included in the table as these treatments were only investigated during one season.

Topsoil

In 2021 at Minnipa, plants in plots treated with CCM had the highest yield (3.44t/ha), while those treated with continuous P (3.24t/ha), ‘high_seedrate_fungicide_bandedN_phosacid_TEs’ (3.27t/ha) and phosphoric acid plus trace elements (3.19t/ha) also yielded higher than typical practice (2.82t/ha). At Poochera, only plants in the ‘high_seedrate_fungicide_bandedN_phosacid_TEs’ (3.27t/ha) and CCM (3.09t/ha) treated plots had higher yields than those in the control plots (2.66t/ha). At Port Kenny, CCM (2.42t/ha) and the ‘high_seedrate_fungicide_bandedN_phosacid_
TEs’ treatment (2.38t/ha) were the highest yielding treatments. The high seeding rate treatment (2.07t/ha) also yielded better than the control (1.7t/ha).

In 2022, Port Kenny was the highest yielding topsoil trial with mean barley grain yield of 4.09t/ha. ‘High_seedrate_fungicide_bandedN_phosacid_TEs’ produced the highest barley grain yields at Minnipa (4.37t/ha) and Poochera 4.17t/ha). At Port Kenny, CCM 500kg/ha resulted in the highest barley grain yields (4.76t/ha) and consistently yielded better than typical practice across all three sites. A positive P response was evident at Minnipa and Port Kenny because ‘Continous_P’ and ‘Phosacid_TEs’ yielded better than typical practice at these two sites. Microbial seed-coating was the only treatment in the topsoil trials that yielded lower than typical practice.

‘High_seedrate_fungicide_bandedN_phosacid_TEs’ had more accumulated yield at all three sites. Cumulative change in grain yield relative to typical practice was 1.13t/ha at Minnipa, 1.54t/ha at Poochera and 1.34t/ha at Port Kenny (Table 1). CCM applied in 2021 at 500kg/ha resulted in the highest change in grain yield (1.99t/ha at Poochera) of all treatments.

Deep P highlights

• Barley and triticale performance improved strongly with P fertiliser on a deep sand with almost no P reserves.
• Barley performed better when P fertiliser was banded just below the seed row rather than when P was banded 20cm below the soil surface.
• Yields with deep P were generally lower than yields with shallow P at the same rate.
• The residual benefits of P applied in previous years to crop production were very poor relative to freshly applied P regardless of application strategy in most trials, and there has been very little evidence of deep P having superior residual benefits.
• A delay in P acquisition can cause a decrease in crop yields in a very P responsive situation.

Discussion and recommendations

After two years of conducting these trials, crop responses to the more costly subsoil strategies are smaller and less likely in highly calcareous soils with underlying physical, biological, and chemical constraints.

Ameliorating high soil strength by deep ripping has proven to be less effective on these types of soils than on other sands. There can be a penalty from physical disturbance using deep rippers and inclusion plates, as a result of a rough seed bed. Even where crop establishment following ripping has been reasonable, benefits from deep physical disturbance have been small or absent. This is supported by only moderate penetration resistances of under 3000kPa to a depth of 40cm at all the sites. Values much higher than this are common in siliceous sands where deep ripping is producing large crop production increases compared to the control.

In highly calcareous soils, the incorporation of organic amendments (Neutrog and CCM) into subsoils has shown potential to improve crop production but is still economically dubious. However, this response needs to be validated over more situations to determine their wider impact on longer-term crop productivity and profitability.

Several short-term and cheaper topsoil strategies have good potential to increase crop vigour and productivity in upper EP environments. Plant populations, crop biomass and grain yields can be improved by higher sowing rates, providing that the denser plant populations are supported by improved nutrition (N and P and trace elements). CCM boosted crop vigour and biomass production when placed just below the seed. We believe that at least part of the benefits from this CCM is to deliver P to the crop in a more effective way than current mineral fertilisers. The availability of P in these challenging soils is always low and several other treatments with higher P also improved crop production. CCM at a lower rate (100kg/ha) did not perform as well as the initial higher rate of 500kg/ha, but the residual benefits of CCM were very good. Further investigation is needed to determine how best to apply CCM, how low rates can be applied to improve crop growth and productivity, what forms of CCM are effective, and how important is P enrichment to their performance.

Key recommendations

• Crop responses to the more costly subsoil strategies are smaller and less likely in highly calcareous soils with underlying physical, biological and chemical constraints. Therefore, the focus should be on short-term topsoil strategies to improve early crop vigour, biomass and grain yield.
• The use of higher sowing rates is an effective strategy to improve plant population, crop biomass and grain yield, providing that the denser plant populations are supported by improved nutrition (N and P and trace elements).
• CCM placed just below the seed is another effective strategy to improve early crop vigour, biomass and grain yield. Residual benefits were very good. Further investigations are needed to fully define their residual benefits, determine how best to apply them and how low they can be applied to improve crop growth and productivity. This product is not commercially available.
• Ameliorating high soil strength by deep ripping has proven to be less effective on these types of soils than on other sands, therefore the recommendation is to identify and understand the underlying subsoil constraints before making the decision to deep rip.
• To be a viable option for growers, deep P needs to not only match the performance of shallow P, but also improve on it to justify the extra effort of placing P deep.

Acknowledgements

This project, ‘More profitable crops on highly calcareous soils by improving early vigour and overcoming soil constraints’ is supported by the Cooperative Research Centre for High Performance Soils whose activities are funded by the Australian Government's Cooperative Research Centre Program and GRDC. The authors would also like to thank the landholders and families involved in this project: Chad Gosling, Simon Guerin, and the Minnipa Agricultural Centre.

References

Dzoma B, Wilhelm N, Cook A, Richter I, Standley C (2021) More profitable crops on highly calcareous soils by improving early vigour and overcoming soil constraints. Eyre Peninsula Farming Systems Summary 2021, page 44.

Dzoma B, Wilhelm N, Cook A, Richter I, Standley C (2022) More profitable crops on highly calcareous soils by improving early vigour and overcoming soil constraints. Eyre Peninsula Farming Systems Summary 2022, page 29.

Contact details

Brian Dzoma
brian.dzoma@sa.gov.au