How can amelioration affect crop uptake of nutrients in gravel soils?
By Kate Parker, Nathan Craig & Simon Kruger
In 2024, one of our primary trial sites has been Tim Creagh’s gravel soil paddock in Dandaragan. Tim, alongside the West Midlands Group (WMG), has been investigating how various soil amelioration methods can combat increasing water repellence in his gravel soils as part of the GRDC funded Soil Water Repellence Project. Four different methods have been tested this year: inversion tillage with a Plozza Plow, deep ripping with delving plates (Nufab deep ripper – both single and a double pass), and mixing and delving with the Plozza ‘Fanger’. While the main focus of this GRDC-funded project is to address soil water repellence, it also provides valuable insights into how these techniques influence nutrient uptake.
Impact of Soil Amelioration on Crop Nutrition
Recent research (Scanlan 2024) from various sites across Western Australia (including Wathingarra, Dandaragan, Badgingarra, and Regans Ford), has shown that mechanical soil amelioration significantly impacts crop nutrition and fertiliser management. Techniques like deep ripping and rotary spading can enhance nutrient availability by redistributing nutrients within the soil profile and improving root access to previously unavailable nutrients. This can increase crop yield potential, but it also means that fertiliser application rates may need to be adjusted to meet the increased crop nutrient demands. Preliminary findings suggest that ameliorated soils respond better to fertilisers, particularly nitrogen, which can lead to improved crop performance and profitability. Ongoing studies aim to develop specific fertiliser guidelines for ameliorated soils, considering the spatial variability in nutrient distribution and ensuring optimal nutrient management (Scanlan 2020). Additionally, research into plant responses to nutrient applications post-amelioration is providing valuable insights into long-term fertiliser strategies. These insights emphasize the need for tailored fertiliser management practices to maximize the benefits of soil amelioration.
Effect of Amelioration on Specific Nutrients
The impact of soil amelioration on nutrient availability varies across different nutrients (Bryce, Plusky 2022). Here’s a summary table of how mechanical amelioration can affect key nutrients:
| Nutrient | Impact of Mechanical Amelioration |
|---|---|
| Nitrogen | Release of Nitrogen: Mechanical amelioration techniques can promote the release of nitrogen from organic matter through increased aeration and better soil structure. Methods like deep ripping or mixing stimulate microbial activity, breaking down organic matter and releasing nitrogen in plant-available forms like nitrates and ammonium. While this can improve nitrogen uptake, there is a risk of volatilisation and leaching, especially in sandy soils. |
| Phosphorus | Limited Impact on Phosphorous Availability: Unlike nitrogen, phosphorous is less mobile in the soil and therefore less affected by soil disturbance. It tends to form insoluble compounds with calcium, magnesium, and iron in the soil, making it less available to plants. Therefore, mechanical amelioration may have a limited effect on increasing phosphorus availability, especially in soils that are already high in calcium or iron. However, there can be a risk of increased phosphorus loss via runoff if not managed appropriately. |
| Potassium | Improved Potassium Availability: Potassium, like nitrogen, is a mobile nutrient that can be affected by mechanical amelioration. The process of tillage or deep ripping can enhance the mixing of soil layers, improving the availability of potassium in the topsoil. It can also improve root penetration, which helps crops access potassium more efficiently. However, as potassium is a mobile nutrient, mechanical amelioration can also increase risk of it leaching deeper into the soil profile, out of reach of plant roots. |
| Sulfur | Sulfur Release from Organic Matter: Sulfur is often found in organic forms that require microbial activity to convert it into plant-available forms (sulfates). Mechanical amelioration, such as tilling or mixing, can improve microbial activity in the soil, thereby increasing the rate at which sulfur is mineralized and made available to crops. However, like nitrogen, this process comes with the risk of sulfur leaching. |
2024 Trial Results
Nutrient levels (Nitrogen, Phosphorus, Potassium, and Sulfur) were analyzed in two ways: kg/ha and percentage composition. The kg/ha of nutrients is calculated by overlaying the percentage uptake with the amount of biomass produced at each sampling stage. Kg/ha indicates the physical amount of nutrients taken up from the soil and any fertiliser applied whilst percentage uptake helps determine if a crop is deficient in any nutrients.
Figure 1 shows the nutrient uptake in kg/ha for nitrogen, phosphorus, potassium, and sulfur across all treatments. The data indicates that at Growth Stage 30 (GS30), all ameliorated treatments had higher nitrogen uptake than the control, with the Fanger, Nufab, and Nufab double pass treatments showing the most significant differences. At peak biomass, ameliorated treatments still had higher nitrogen levels, with the Fanger treatment showing the largest difference. For phosphorus, there were no significant differences between treatments. Potassium uptake was significantly higher in the Plozza Plow and Nufab double pass treatments at GS30, but by peak biomass, differences were deemed not significant. This means that although visually the graph shows large differences between the control and ameliorated treatments, there was a high level of variability in the results leading to the error bars overlapping. Sulfur levels at GS30 were significantly higher in the Nufab single pass treatment compared to the control, and at peak biomass, both the Fanger and Nufab single pass treatments were significantly higher than the control.
Figure 2 shows the percentage composition of nutrients for each treatment. The only differences observed were at GS30 for Nitrogen and Sulfur. This means that for the insignificant results in the phosphorous and potassium graphs, the differences seen in kg/ha graphs (Figure 1) are due to differences in biomass production. The Fanger and Nufab double pass treatments showed the most notable differences for nitrogen and sulfur, indicating that these amelioration methods may enhance nutrient uptake, particularly at early stages of crop growth. Although visually the graphs for potassium seem different, there was high variability meaning any differences are not significant.
Discussion
While some ameliorated treatments showed improvements in nutrient uptake, particularly for nitrogen and sulfur, the variability of results suggests that further research is needed to better understand the long-term effects of these methods on nutrient availability and crop performance.
Assumptions about amelioration would be that increased nutrient uptake and percentages would mean a decreased need for fertiliser. This may be untrue, with amelioration just moving the bar up for yield potential leading to a possible increase in fertiliser needs to get the highest potential out of the ameliorated soils. Mechanical amelioration methods can significantly influence the availability of nutrients in the soil by improving soil structure, enhancing microbial activity, and facilitating nutrient release. The impact varies for each nutrient:
- Nitrogen and sulfur are more likely to show positive responses due to increased microbial activity.
- Phosphorus and potassium responses are more complex and depend on soil conditions.
These nutrient interactions are reflected in the results (Figure 1 and 2), with nitrogen and sulfur showing the most significant differences in nutrient uptake between ameliorated treatments and controls, while phosphorus and potassium exhibited smaller differences. This raises the question: if crops are taking up more nitrogen and sulfur, should fertiliser application rates be reduced, or will increased crop and root growth necessitate more inputs? Similarly, with increased yield potential, does this mean that higher proportions of phosphorus and potassium are needed, or would this be less effective due to the low response?
It is also important to consider the potential for soil depletion. Increased nutrient uptake from amelioration could deplete soil reserves, potentially putting the paddock at a disadvantage in future seasons. With amelioration improving nutrient availability, it is essential to ensure there are sufficient nutrients in the soil to support enhanced crop growth without depleting key resources.
The effectiveness of these amelioration methods on nutrient availability depends on the type of amelioration, soil type, and timing of fertiliser application. To optimise nutrient use, farmers should carefully select and manage mechanical amelioration techniques based on their specific soil conditions and crop requirements.
Key Takeaways for Growers
- Enhanced Nutrient Uptake: Improved nutrient uptake has been observed for Nitrogen and Sulfur in ameliorated treatments which can increase yield potential, but may also require higher fertilizer inputs to support increased crop growth.
- Soil Health Management: Effective soil amelioration can improve soil structure and water infiltration, but care should be taken to avoid soil compaction and erosion.
- Nutrient Management: Understanding the mobility and availability of different nutrients is crucial for optimizing fertilizer use and minimizing losses through leaching or erosion.
- Tailored Approaches: Each soil type and condition, alongside seasonal factors may require a tailored approach to soil amelioration. Regular soil testing and monitoring can help in making informed decisions on fertiliser application and soil management.
- Continued investigation: Further research is needed to better understand the long-term effects of these methods on nutrient availability and crop performance.
Conclusion
In conclusion, the 2024 trial at Tim Creagh’s gravel soil paddock in Dandaragan highlights the significant potential of mechanical soil amelioration methods in enhancing nutrient uptake, particularly for nitrogen and sulfur. While the results so far show promising improvements in nutrient availability, the variability in responses across different treatments underscores the importance of further research. As soil amelioration techniques continue to evolve, understanding the long-term effects on both nutrient management and crop yield potential will be essential for farmers. Continued trials for this project on different soil types are already in the works for the 2025 season. Whilst the focus of this project is Soil Water Repellence, the data of increased nutrient uptake from soil amelioration can assist in enabling more precise recommendations for managing soil health and optimizing fertilizer use to ensure sustainable and profitable farming practices in the future.
References and More Information
Adesanya, T. et al. (2024) ‘Crop rotation diversity and tillage effects on soil and wheat grain nutrient concentration in an organically-managed system’, Journal of Agriculture and Food Research, 18, p. 101411. doi:10.1016/j.jafr.2024.101411.
Angon, P.B. et al. (2023) ‘An overview of the impact of tillage and cropping systems on soil health in agricultural practices’, Advances in Agriculture, 2023, pp. 1–14. doi:10.1155/2023/8861216.
Bryce, A. and Plusky, W. (2022) Mechanical soil amelioration shifts balance for Crop Nutrition, Groundcover. Available at: https://groundcover.grdc.com.au/agronomy/soil-and-nutrition/mechanical-soil-amelioration-shifts-balance-for-crop-nutrition
Fulwood, J. (2020) Soils Research offers glimpse into plant reaction to nutrients, Groundcover. Available at: https://groundcover.grdc.com.au/agronomy/soil-and-nutrition/soils-research-offers-glimpse-into-plant-reaction-to-nutrients2
Manhas, S. et al. (2024) ‘Assessing the impact of tillage practices and nutrient levels on the growth and productivity of ethopian mustard (brassica carinata L.) – soybean (glycine max (L.) merr.) cropping system’, BMC Plant Biology, 24(1), pp. 24–1059. doi:10.1186/s12870-024-05753-7.
Scanlan, C. (2024) Grains convo July 2024 – Uncovering the impact of mechanical soil amelioration on crop nutrition, Grains Convo | Agriculture and Food. Available at: https://www.agric.wa.gov.au/newsletters/grains-convo/grains-convo-july-2024?page=0%2C2#smartpaging_toc_p2_s0_h2
Scanlan, C., Murphy, D. and Hoyle, F. (2020) Fertiliser Guides planned for ameliorated soils, Groundcover. Available at: https://groundcover.grdc.com.au/agronomy/soil-and-nutrition/fertiliser-guides-planned-for-ameliorated-soils
Singh, D. et al. (2020) ‘Effect of reversal of conservation tillage on soil nutrient availability and crop nutrient uptake in soybean in the vertisols of Central India’, Sustainability, 12(16), p. 6608. doi:10.3390/su12166608.
Young, M.D., Ros, G.H. and de Vries, W. (2021) ‘Impacts of agronomic measures on crop, soil, and environmental indicators: A review and synthesis of Meta-analysis’, Agriculture, Ecosystems & Environment, 319, p. 107551. doi:10.1016/j.agee.2021.107551.
