Evaluating the Economics of Soil Amelioration Strategies for Non-Wetting Soils
By Kate Parker & Nathan Craig, WMG
Key Takeaways
- Plozza Plow emerged as the most cost-effective treatment, with the highest yield and return on investment (ROI).
- Soil amelioration treatments outperformed untreated plots, with significant yield increases in 2024.
- Early results suggest that Plozza Plow offers the best financial returns, with the fastest break-even period.
- These results are based on trial data from 2024, and further research is needed to assess long-term benefits.
Introduction
Non-wetting soils are a significant challenge for farmers in the Geraldton and Kwinana West Port Zones. Water repellence on sandy and gravel soils leads to poor crop germination, lower yields, and inefficient fertiliser use. The Soil Water Repellence project is addressing this issue through a Participatory Action Research (PAR) approach, testing various soil amelioration techniques to improve water infiltration and crop establishment. The goal is not just to find effective practices but to evaluate their economic feasibility.
Economic Considerations
While improving soil health is crucial, understanding the economic viability of these practices is equally important. Valuable data on the cost-effectiveness of different treatments, can assist farmers in making informed decisions about which practices to adopt based on their potential ROI.
An economic analysis will assess:
- The cost of machinery and amendments
- Expected improvements in crop yield
- The economic return over multiple growing seasons
This analysis will initially focus on the 2024 season, providing preliminary data to guide farmers. A full economic report will follow at the conclusion of the project, taking into account long-term results.
Challenges and Limitations
- Climate & Soil Type Variability: The results of this trial are based on the specific soil types and climate conditions in the Geraldton and Kwinana West Port Zones across one season. Variations in these factors may influence the outcomes.
- Machinery Costs: The estimated machinery costs are provided by the participating growers, which may vary depending on equipment availability and usage rates.
2024 Economic Analysis Results
The table below summarises key results from the trial conducted at the Dandaragan site in 2024. Peak biomass was measured at the anthesis stage of oats, while grain yield was calculated using the grower paddock yield map at harvest. Gross Margin is calculated using a figure of $390/tonne for milling oats. (This table has been reduced from its original full analysis for ease of reading).
Table 1. Peak biomass and grain yield for each soil amelioration treatment at the Dandaragan site in 2024. Peak biomass was measured at the anthesis stage of the oats while grain yield was measured using the grower paddock yield map at harvest. Gross Margin has been calculated using the grower-based figure of $390/tonne for milling oats.
| Measurement | Plozza | Fanger | Control 1 | Nufab | Control 2 | Nufab Dbl |
| Peak Biomass (t/ha) | 6.8 | 8.9 | 5.5 | 8.5 | 4.7 | 7.8 |
| Biomass benefit (% of average control treatments) | +34% | +75% | 0% | +68% | 0% | +53% |
| Grain yield (t/ha) | 3.2 | 3.0 | 1.8 | 2.8 | 1.6 | 2.8 |
| Yield benefit (% of average control treatments) | +89% | +76% | 0% | +65% | 0% | +64% |
| Harvest Index | 47.2% | 33.6% | 32.5% | 33.1% | 34.7% | 35.8% |
| Yield Income ($/ha) | $1252 | $1166 | $698 | $1096 | $636 | $1088 |
| Gross Margin ($/ha) | $961 | $876 | $408 | $805 | $346 | $798 |
| Capital Investment (estimated by those involved) | $63 | $147 | – | $130 | – | $243 |
| Net difference after investment (Gross Margin) | $491 | $322 | – | $268 | – | $147 |
| Return on Investment (% Return) | 876% | 319% | – | 307% | – | 160% |
| Breakeven period (Years to return on investment)* | 0.1 | 0.3 | – | 0.3 | – | 0.6 |
- Plozza Plow Treatment: This treatment achieved the highest average yield (3.21 t/ha), an 89% yield increase over untreated plots, and delivered the best ROI with a break-even period of just 0.1 years—the shortest among all treatments. Despite lower operational costs, this treatment provided remarkable returns for farmers.
- Fanger Plow Treatment: While it also showed good yield improvement, it had higher costs and a longer break-even period compared to the Plozza Plow.
- Nufab Rip/Delve Treatments: These treatments also provided yield improvements, but they required higher investment and had longer payback periods.
The economic analysis confirmed that the Plozza Plow offered the highest ROI (876%), delivering substantial returns with minimal additional investment. The treatment required less fuel and machinery time, making it highly efficient for farmers.
The Plozza Plow treatment this year has demonstrated a low operational cost, quick break-even period and high yield benefit. The gross margin for this treatment also showed the most significant increase, reinforcing its value as a profitable soil amelioration technique.
While the 2024 results are promising, further research will be crucial in understanding the long-term benefits and sustainability of these treatments. The soil types, rainfall patterns, and other variables across the region can affect the long-term effectiveness of these approaches. Ongoing monitoring and trials will provide more clarity on how these treatments hold up over multiple seasons and under different conditions.
Harvest Index
Harvest index (HI) is the ratio of harvested grain to the total dry matter of a plant’s shoots. It’s a measure of how efficiently a plant reproduces. In Australia, a considered “ideal” harvest index for most cereal crops, like wheat, is typically between 0.30 and 0.45; meaning that 30-45% of the total plant biomass is made up of harvestable grain (Hunt et al., 2012).
The Plozza plow treatment had a relatively high harvest index (Table 1) indicating better yield efficiency and larger proportion of biomass allocated to harvestable product. This also indicates the treatment has allowed more balanced conditions for the crop as the crop has put more resources into producing grain rather than overall growth. Although the other amelioration treatments showed higher biomass, their lower harvest indexes could be due to the lack of rainfall at a critical point in the season (24 days in September with no rainfall) (Table 2).
The deep ripping/delving mixing mechanisms of the Fanger and Nufab treatments do allow for better root penetration and subsequent nutrient and water use however, the increased growth and biomass from this may not be able to be sustained in stressful conditions (i.e. low rainfall at critical timing).
Studies have shown links between harvest index and % of water use after anthesis (Unkovich et al., 2006; Sadras & Connor, 1991). The disced inversion mechanism of the Plozza plow may not reach as deep or reduce as much soil strength but provides a more consistent and balanced nutrient and moisture distribution closer to the surface.
Overall, the 2024 seasons data from the Dandaragan trial site shows that the Plozza plow treatment has allocated more resources to reproductive structures rather than vegetative growth than other treatments allowing for a higher harvest index.
Table 2. Monthly rainfall in 2024 and the long-term average (LTA 2005-2024) at the closest weather station to the trial site. (Nambung station (009276) – BOM)
| Month | Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | Annual |
| 2024 | 0 | 2 | 3 | 8.2 | 45.2 | 124.5 | 140.3 | 99.7 | 8.8 | 45.0 | 6.0 | 0.8 | 484 |
| LTA | 13.2 | 17 | 17.8 | 17 | 61.6 | 90.5 | 102.2 | 85.1 | 44.6 | 24.9 | 13.4 | 11.8 | 514 |
Conclusion
The trial’s results show that ameliorating non-wetting soils doesn’t just improve crop yields—it can also boost farm profitability. The soil amelioration treatments in this study demonstrate that adopting any of the methods is more profitable than continuing without them. Among the treatments tested, Plozza Plow emerged as the most cost-effective option, offering significant financial returns for farmers looking to improve yields in non-wetting areas. However, the 2024 season, with its late season break and low September rainfall, may not fully reflect the potential long-term benefits, especially if rainfall had been higher. This underscores the need for caution in interpreting the results, as rainfall variability can significantly impact crop yields.
The study also highlighted differences in the cost and effectiveness of soil amelioration methods. The Nufab ripper, which works to a depth of 60cm, had higher costs due to equipment hire and fuel but may offer long-term benefits due to deeper soil loosening. Practicalities, such as equipment accessibility and costs, need to be considered when choosing a method. Additionally, the study’s limitations, including reliance on data from a single season and assumptions about stable input costs, suggest that long-term studies are necessary for a more accurate economic assessment.
Future research could focus on multi-season studies to assess the durability of the findings, explore other agronomic factors, and examine how soil amelioration interacts with other farming practices. A broader economic analysis, considering equipment depreciation, labour, and regional market dynamics, would provide a more comprehensive understanding of the financial impact.
As these treatments continue to be refined and tested, farmers in the Geraldton and Kwinana West Port Zones can look forward to practical, science-backed solutions for managing non-wetting soils, improving their bottom line and increasing knowledge and confidence in managing non-wetting soils.
Next Steps
- Ongoing Monitoring: Data will continue to be collected on this trial site through to the end of the 2026 season, providing a clearer picture of the long-term impacts of the amelioration practices. More trial sites will be established across the region on varying soil types to further assess soil amelioration options.
- Follow-Up: Farmers interested in participating or learning more should contact projects@wmgroup.org.au for further information.
References
Hunt, J., Brill, R., & DPI, N. (2012). Strategies for improving water-use efficiency in western regions through increasing harvest index.?Department of Primary Industries (DPI) NSW, Australia, p10.
Unkovich, M. & Baldock, Jeffrey & Forbes, Matthew. (2006). A review of biological yield and harvest index in Australian field crops.
Sadras, V.O. and Connor, D.J., 1991. Physiological basis of the response of harvest index to the fraction of water transpired after anthesis. A simple model to estimate harvest index for determinate species. Field Crops. Res., 26: 227-239.
