Soil amelioration- is it the right fit for you?

Demi Taylor

In 2023, BCG undertook a soil amelioration demonstration near Natimuk, VIC, in collaboration with Agriculture Victoria. The demo site incorporated a range of different soil amelioration strategies, including ripped and surface applied commercial compost, host growers compost and gypsum. Watch the video below for a full overview of the project:

As part of this project, assessments were taken for crop establishment, flowering and maturity biomass, crop yield and grain quality, and results are outlined below.

Crop establishment 

Crop establishment results showed that when ignoring position in the land system, there was no differences between the treatments. However, when considering position in the land system on the dune, crop establishment was poorer in the deep ripped treatments that had not been speed tilled, in comparison to the control. This highlights that sowing bed preparation is important for improved crop establishment after ameliorating soil.  

On the swale, surface applied and deep ripped manure resulted in a general increase in crop establishment. Likewise, so did the deep ripped treatment alone, indicating that either the chemical or physical soil constraints in the swale region of the paddock were being addressed by some of the soil ameliorants.  

In addition, there were no differences on the mid-slope.  

Flowering and maturity biomass 

Flowering biomass results showed there was not much difference between treatments. The only evident trend was an average increase of 1.3t/ha of flowering biomass in the gypsum treatments, when compared with the control. This was relatively consistent across all land systems.  

Both surface applied and deep ripped manure treatments had a positive influence on crop biomass at maturity.  

The deep ripped pig manure compost increased maturity biomass by an average of 3.8t/ha, in comparison to the control over all the land systems. This treatment also had the greatest effect on the mid slope, with an increase in crop biomass of 5.5t/ha.  

Gypsum, both deep ripped and surface applied, as well as deep ripping alone didn’t appear to impact crop maturity biomass. 

Crop yield  

In terms of crop yield, deep ripping alone, as well as all treatments incorporating the pig manure or host growers compost showed a positive impact on crop yields, when compared to the control.  

On average across the land systems, the deep ripped pig manure treatment increased yields the most, by 1.5t/ha when compared with the control.  

The greatest benefit to yield was again seen on the mid-slope in the deep ripped and pig manure treatment, with an increase of 2.1t/ha.  

Grain quality  

In terms of grain quality, there was no evident treatment impact. All test weights were above 65 kg per hectolitre, screenings below 5%, retention above 70% and moisture below 12.5%.  

All protein levels measured in at below 9%, and therefore, under MALT standards. However, there was a trend towards increased protein from the manure treatments, both deep ripped and surface applied.  

Commercial practice and on-farm profitability  

Our key message to growers when looking to undertake soil amelioration techniques, is that it’s important to understand the soil constraint limiting production, as well as the most appropriate amelioration strategy to address this. Failure to do so may result in wasted time and money if no returns are realised

Like the Natimuk demonstration, trialling different techniques on a small scale to understand the crop response is a valuable tool to determine if there is a yield increase. This can increase grower confidence prior to making major investments in ameliorating the whole or part of the paddock.  

Ripping to address compaction  

Ripping can be used to ameliorate soils that have hard pans or compacted layers that are restricting root growth. By mechanically breaking up the hard soil, ripping allows the crop roots to grow deeper, potentially increasing the crops access to moisture and nutrition. For ripping to be effective, the tynes on the equipment must be able to penetrate below the compacted layer (this can differ between rippers).  

To determine where in the soil profile the compaction is, it is suggested that growers use a penetrometer or a shovel/stick to measure. It is also recommended that if the compacted layer is at a depth that the ripping equipment can achieve, growers are encouraged to rip test strips at least one season prior, rather than ripping the whole/zone paddock. 

Potential considerations when ripping  

Be aware that in drier seasons, ripping can increase the risk of the crop haying off. This is because the roots gain access to soil moisture earlier, resulting in more vegetative growth, while constricted roots may use water slower.  

Decreased crop establishment can also be a negative consequence of ripping due to variable seeding depth. If sowing into recently ameliorated soils, seeder set-up is important to ensure seeding depth is correct. A potential solution may be to roll ripped soils prior to sowing (or in this demo’s case, speed till the area) to provide a more level seed bed. When doing so, growers need to remain mindful to minimise re-compacting the soil. Another alternative may be to increase seeding rates to compensate for lower establishment rates.  

Another consideration with ripping is the likelihood of increased herbicide damage due to loose soil, variable seeding depths, and a lack of organic matter for the herbicide to bind to. 

The timing of ripping is also an important consideration, not just in terms of crop rotation, but also soil condition. The best crops to sow in the first-year post ripping are cereals and pulses, as they can handle a more uneven seeding bed. 

Ripping saturated soil profiles leads to smearing and not effectively shattering the hard pan, therefore, to maximise the ripping response it is suggested to rip soils that are not saturated, but also not completely dry (unless you like burning diesel!).   

Ripping can also expose crop roots to unwanted subsoil characteristics. It is therefore important to test the soil to at least 1m in increments to check for underlying issues such as poor nutrient levels, sodicity, salinity, boron, or unfavourable pH. If there are additional constraints, a different amelioration strategy may need to be adopted, or none.  

To learn more about ripping to correct layers of high soil strength, read this GRDC resource.

Amelioration to address poor nutrition/sodicity in the subsoil 

Manure is a common source of organic matter used for amelioration, however, other sources such as nutrient treated crop stubbles and composts are increasingly being used successfully.

Subsoil amelioration is an amelioration strategy that can be used to alleviate poor subsoil nutrition. It is a practice developed following research undertaken to ameliorate dense, sodic clay subsoils in the high rainfall zone of southwest Victoria. This strategy involves the incorporation of high rates of high-N organic material, such as poultry manure (up to 20t/ha fresh weight). The amendment is placed in rip-lines up to one metre apart into the upper layers of the clay sub soil.  

The addition of manure/compost can be a valuable soil ameliorant and fertiliser. It is, however, important to have manure tested at a lab before applying it to a paddock, to ensure it does not contain anything harmful, such as low pH (acidic), high salt levels, or boron which may reduce yields. Interpreting the amount of P, K and S that the crop will get from manure can also be difficult, as the lab results will include the total amount of P, K or S, and not necessarily the amount that is available to plants. If growers can acquire testing for nitrate and ammonium in the manure as organic compounds (some will be released, some will not) and testing for total N, it will help show this. It is important to carefully manage N inputs in the first season to ensure the crop doesn’t hay off from excess N, and to note that conventional synthetic fertiliser at sowing may still be needed to ensure crop demands are met. 

It is also important to ensure the manure is not contaminated with weed seeds or other biosecurity hazards before spreading it across the paddock. Keep records of test results, manure application rates and yields to allow comparison of the benefits and costs against synthetic fertiliser. 

Subsoil amelioration: on-farm adoption 

Whilst there is growing interest in subsoil manuring due to its sometimes-large increases in crop yields on-farm, adoption is currently low. This lack of adoption has been linked to logistical constraints such as being able to source and transport enough manure or compost, as well as a lack of suitable commercial scale machinery for placing the ameliorants into the subsoil. Transport and application cost can be high compared with synthetic fertiliser. The low nutrient density of manure means its economical application is limited to paddocks located close to the source. 

The other main factor is the unpredictability of grain yield responses (when, where, how much, and for how long) which means many farmers are not willing to undertake the significant financial risk resulting from the initial high upfront investment needed. 

Soil amelioration costs

Growers are encouraged to take the time to calculate costs for their own specific location and equipment, given the variability in pricing and application of these amendments.  

  • Ripping costs can be around $100-$200/ha if dry ripping (Bryce, 2020) 
  • With manure costs, it is important to factor in product cost, transport costs and spreading/application costs. The Bio Gro compost was $65/t (delivery included).  
  • Sale and Malcom (2015) estimated a total cost of approx. $1,200-$1,400/ha for sub soil manuring.  

To learn more about subsoil amelioration, read this handy GRDC resource. 

Click here for a soil amelioration decision support guide for grain growers.

This project was delivered in collaboration with Agriculture Victoria, through funding from the Australian Governments National Landcare Program: Smart Farms Small Grants: Soil Extension Activities, and GRDC.

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