Capturing the benefit of increased plant growth following amelioration
By Kate Parker, Nathan Craig & Simon Kruger
In 2024, one of our primary trial sites has been located on Tim Creagh’s property in Dandaragan on a shallow sand over gravel duplex soil. This site has been exploring how various soil amelioration techniques can help address the increasing water repellence on gravel soils. The trial includes four different amelioration methods: inversion tillage using a Plozza Plow, deep ripping with delving plates (Nufab deep ripper – both single and double pass), and mixing and delving with the Plozza ‘Fanger’. These strategies have three primary benefits to the soil: inversion or mixing of the soil to reduce soil water repellence, mixing of nutrients and amendments deeper in to the soil profile, and removal of soil compaction. Following the amelioration treatments, the site was sown to oats with the option of harvest for grain or cut for hay.
While the main goal of this GRDC-funded project is to explore new strategies for mitigating soil water repellence, it also provides valuable insights into the impact of these amelioration techniques on dry matter production of various crops which can be used as forage crops and hay. This article explores the potential benefit that soil amelioration can have on soil strength and crop biomass production, and how this could benefit a grain-and-graze, cereals-as-pasture, or hay production system.
Managing soil water repellence is a key strategy in our region to increase crop growth and grain yield. Due to the relative stable relationship between the two (i.e. the harvest index), grain yield and crop growth are generally aligned meaning that high yielding crops tend to also grow a lot of biomass. This increase in biomass creates an opportunity for multiple uses, such as grain-and-graze systems that provide additional sources of income from the crop and benefits for the livestock enterprise. Recently, there has also been an increase in the use of cereals as pasture species across the West Midlands region as they have higher biomass production compared to other pasture species and addressing soil water repellence can have direct pasture benefits as well. If crop and pasture production can be maximised by addressing soil water repellence, crop yields can be higher and more feed can be grown to support a larger number of stock, enhancing the overall productivity of the farm.
In the short term, we know that tillage can lead to a noticeable increase in plant biomass because it helps break up the soil and makes it easier for plants to establish themselves and grow. This can be particularly beneficial for establishing new pastures or in areas with poor soil structure. The soil type at the site was a shallow sand over a dense gravel subsoil which had very few rocks present, and this meant that the soil strength was very high down the soil profile (Figure 1). The control treatments highlight that root growth would start to become limited at 175mm soil depth where soil strength exceeds 2500kPa (red dashed line). The amelioration treatments have effectively increased the unrestricted root growth layer to 250-400mm depth.
All ameliorated plots tended to have a higher biomass than the control plots, with the highlight being an increase of 58% for the Nufab (single pass). In comparison, the common method of ameliorating this type of soil (Plozza plow) was only 26% higher. This difference between Nufab (single pass) is likely due to the increased depth of loosening of topsoil compared to all other amelioration treatments.
At the flowering stage of the crop, the Fanger and Nufab (double pass) double treatments had caught up to the Nufab (single pass) treatment compared to the GS30 stage and were significantly higher than the control treatments. When compared to the control, the Fanger and Nufab (single pass) treatment increased plant biomass production by a whopping 75% and 68% respectively.
The results confirm that amelioration treatments can significantly reduce soil strength, allowing increased plant biomass production. This is particularly important on this soil type which contained a dense gravel layer impenetrable with a shovel beyond 10-15cm limiting plant growth. The Nufab (single pass) was the most effective treatment to improve biomass production and this is likely due to the mechanical action the machine has in the soil. The Nufab ripper had delving plates on the ripping tines which mixed the soil and likely led to the large reduction in soil strength down to 400mm. However, the ripping tines extended down to 550mm soil depth, providing loose soil in pockets where the ripping tines had traversed (Figure 4). In comparison, the Plozza plow was effective at reducing soil strength in the top 30cm, but owing to the mechanical disc action in the soil, did not have any effect on the subsoil. Interestingly, a double pass of the Nufab ripper was not better and it is unknown why this was the case, although this treatment had a significantly higher percentage of gravel present in the topsoil after being ameliorated. It is important to note that this gravel soil largely had an absence of rock in the subsoil and this would affect the performance of the Nufab ripper. Further work is needed to understand the impact of all soil amelioration treatments on the chemical and physical properties of a gravel dominant soil type.
The positive benefit of any type of soil amelioration on crop biomass production can be clearly seen at this site for the 2024 season. The effect can be seen for both early and late season biomass production and this creates many opportunities for adding value in a mixed cropping/grazing system. Early feed can be increased through soil amelioration where the soil is loose immediately following treatment and this can be of benefit in a grain and graze situation where the crop is being grazed by livestock early in the season.
A downside to increased biomass production is the potential for the crop to ‘hay-off’ later in the season where crop growth is far greater than the soil and soil moisture can support, resulting in low grain yield. In-crop grazing to reduce biomass has been shown in the grain-and-graze program to lessen the impact of this and could be an effective strategy where biomass production is greatly increased from soil amelioration. However, in the case of hay production or cereals sown as a pasture species where crops ‘haying-off’ is not an issue, greater biomass production has little downside risk. Improved pasture production in the first year following soil amelioration can greatly assist in covering the cost of the amelioration if this biomass production can be efficiently converted into salable product (i.e. meat, wool). Future work on the economics of hay and cereals-as-pasture to pay back the cost of amelioration similar to the yield uplift in cropping systems may uncover alternate methods to pay for most of the cost of amelioration in the first year.
An additional side benefit of increasing pasture production is an increase in soil ground cover to protect the soil and increase soil health, which has been highlighted as an issue in our region over the past few years. Care should be taken when grazing following amelioration to ensure that 50% groundcover is maintained during the season as this can negate the risk of wind erosion in the region.
These findings align with broader agricultural principles, where improved soil conditions typically lead to higher crop growth, better yield potential, and the possibility of using crops for additional purposes such as grazing or pasture species. Further monitoring and research will help to refine these findings and confirm the long-term benefits of these practices for managing water repellence and improving soil fertility.
If you’d like to learn more about the overall purpose and aim of the Soil Water Repellence Project click here.
If you’re looking for an in-depth look at each of the amelioration methods used and what was discussed at the first site crop walk click here.
If you’re interested in getting more information on soils, workshops and related events click here.
