Take home messages
- Achieving consistent and optimal ripping depths is difficult in dry soil conditions, which
has the effect of restricting root access to stored soil moisture and nutrients. - Ripping sand in sandy loams to 20cm in the Southern Mallee delivered no yield advantages
in 2018. Under wetter conditions this may not be the case due to better penetration from
the ripper and greater yield potentials. - Further monitoring is required to determine any future benefits.
Background
Historical soil compaction has been identified to limit crop production in Mallee soils however, how widespread the issue is unknown (Sadras et al. 2004). Drawing from experiences in the Western Australia wheatbelt, years of repeated random traffic over broadacre cropping land with heavy machinery has contributed to the formation of compacted layers within the soil profile (Davies et al. 2018). Compacted layers are commonly found 30cm or deeper; these layers prevent deep infiltration of soil moisture and restrict roots from accessing nutrients and water below this layer. One remediation option is mechanically breaking up and shattering the soil hardpan by deep ripping.
Deep ripping involves pulling narrow tines through the soil profile at a depth of >30cm without
inverting the soil. Advantages from deep ripping have been reported to last for about three seasons on loamy sands and sandy clay loams (Hamza & Anderson 2003). This practice has also been used in controlled traffic farming (CTF) systems where the benefits from ripping are prolonged (anecdotally reported up to 10 seasons on light sandy soils) due to the land not being re-trafficked (Bakker, Davies & Isbister 2017). Improvements in grain yields of 11% from shallow ripping (30-40 cm) and up 44% from deep ripping (50-70 cm) have been observed on deeper sands and loamy sands from the low rainfall zones (LRZ) in Western Australia (Davies et al. 2017).
As part of a larger project looking at increasing the adoption of CTF in the LRZ a trial was established in the southern Mallee region of Victoria to assess the utility of deep ripping on sand and sandy loam soil types by comparing deep ripping to CTF and conventional practice (shallow cultivation).
Aim
To determine if deep ripping has the potential to remediate historical soil compaction and increase yield potential of broadacre crops in the southern Mallee.
Paddock details
| Location: | Woomelang |
| Crop year rainfall (Nov-Oct): | 325mm (annual rainfall) |
| GSR (Apr-Oct): | 217mm |
| Soil type: | Sandy loam to sand |
| Paddock history: | Hurricane lentils (2017) |
Trial details
| Crop type: | Scout wheat |
| Treatments: | Refer to Table 1 |
| Target plant density: | 140 plants/m² |
| Seeding equipment: | Knife points, press wheels, 25cm (10 inch) row spacings |
| Sowing date: | 25 May 2018 |
| Replicates: | Six |
| Harvest date: | 16 November 2018 |
Table 1. Treatments imposed at the Woomelang site in 2018.
Trial inputs
Trial managed as per growers on-farm practice.
Method
A replicated field trial was sown on a grower’s CTF property near Woomelang. The grower has been slowly transitioning from a 9m to 12m wide system over the last 10 years. The soil was not remediated when CTF was adopted and a diverse range of soil types are present across the property with some potentially self-mulching. Using a complete randomised block design, the trial was repeated over two different soil types, a brown sandy loam over loam on the flat and a light brown sand over sandy loam on the rise, both of which are not self-mulching. The treatments were imposed on the 28 March 2018 under dry conditions. Soil samples were taken prior to sowing for nutrients (data not shown). Assessments included establishment counts, crop biomass (at GS70) and grain yield parameters from harvest cuts.
Results and interpretation
The average depth of disturbance by the tines was 20cm, which was less than the targeted depth of >30cm. The reduced penetration is potentially due to a combination of limited available soil water, soil type and insufficient horsepower of the tractor. Despite this, the deep ripping showed that the soil profile was compacted, where it was suspected that root growth was restricted as large clods of soil were brought to the surface.
Across the four treatments there were no significant differences in plant establishment, biomass at flowering and maturity or grain yield and its components (Tables 2 and 3). There was a soil type effect, with the sand having significantly higher biomass and yield compared to the sandy loam. In a more favourable year the differences across the treatments may be larger (higher yield potentials). Furthermore, the reduced depth the deep ripping reached in this trial may have not been sufficient to increase the crop roots access to moisture deeper down the profile. Ongoing monitoring is required to determine any medium to long-term benefits.
Table 2. Crop establishment, biomass and grain yield after deep ripping on the sand at
Woomelang in 2018. Parentheses indicate percentage change compared to the control.
Table 3. Crop establishment, biomass and grain yield after deep ripping on the sandy loam at Woomelang in 2018. Parentheses indicate percentage change compared to the control.
Commercial practice
Appropriate variety selection and soil conservation practices have seen significant yield improvements in the southern Mallee with further gains potentially achievable by remediating historical soil compaction in responsive soils via deep ripping. The cost of deep ripping has been calculated to range from $40 to $50/ha on sandplain soils (Bakker, D, Davies, S & Isbister, B 2017). Clear yield gains are therefore required to make the practice economically feasible.
In the southern Mallee of Victoria, it remains uncertain as to the value of deep ripping in combination with adopting a CTF system. From this trial there appears to be no yield advantage and therefore no improvement to on-farm profitability and sustainability. However, ongoing research in the northern Victorian Mallee and the South Australian Mallee is demonstrating positive yield responses from deep ripping on deep sandy soils.
Due to the costs associated with deep ripping there are several considerations that growers should investigate before putting tines in the ground to make sure the time and dollars invested are returned.
One of the main considerations is soil type. A link between soil type and deep ripping response is commonly reported where sandy soils typically have the greatest response, while red loams and black vertosols show very few positive responses to deep ripping (GRDC 2009). Not all soils will respond positively to deep ripping every season (GRDC 2009). In the Mallee, undertaking soil tests to depth before deep ripping is advisable as some of the alkaline soils have salinity issues and high boron levels at depth creating a hostile environment for crop roots and the potential to also reduce the topsoil quality if deep ripped.
Identifying the presence of a compacted layer and its depth is also important so that the tines rip just below. Using a soil penetrometer can help to determine this. Other considerations include the soil moisture content and timing of operations as a moist soil (not saturated) allows for easier ripping, and optimal timing helps with soil preparation before seeding and therefore better crop establishment. When integrated into the crop sequence, deep ripping can also influence yield responses with anecdotal reports of lentils and wheat performing well after ripping, but canola very poorly (mostly associated with establishment issues). Machinery setup also requires thought as shallow leading tines on the deep ripper may be required to help achieve the desired depth of disturbance and reduce the draft force, helping to keep running costs down.
References
Davies, S, Bakker, D, Lemon, J & Isbister, B 2018, ‘Soil compaction overview’, DAFWA.
GRDC 2009, ‘Deep ripping not appropriate for all soil types’, Deep Ripping Fact Sheet.
Acknowledgements
This research was funded collectively by the GRDC and Agriculture Victoria as part of the Regional Research Agronomists program ‘Improving practices and adoption through strengthening D&E capability and delivery in the southern region’ (DAV000143) in conjunction with the GRDC-funded project ‘Application of CTF in the Low Rainfall Zone’ (ACT00004). We also gratefully acknowledge Darrell Boxall and family for the donation of their time and land.
