Deep ripping is most effective in deep sandy-textured soils where roots need to grow deep to access subsoil moisture. Deep ripping is of particular benefit when it is used to break through a compacted pan or distinct constraining layer, allowing root access to unconstrained soil water beneath this layer.
If the soil below the depth of ripping contains other constraints, such as acidity, poor structure from sodicity or subsoil salinity, the benefit of deep ripping will be limited. The addition of soil ameliorants such as lime or gypsum may be required to stablise the soil. It is possible to inject lime into acidic subsurface soil behind deep ripping tines, however, this is a slow operation and difficult to implement at a large scale (shallow leading tine rippers are ideally suited for this).
Costs and benefits
Grain yield responses to deep ripping on deep sands and sandy earths have tended to be large and reliable, especially in the high and medium rainfall (greater than 350mm) areas. Benefits from deep ripping these soils appear to last for at least three years, depending on crop rotation and soil type.
Deep ripping of heavier textured soils such as the sandy clay loams, loams and even sodic clays has often been considered to be less reliable. More recent research has shown that the yield responses to deep ripping can be large in the year the soil is ripped although the benefits of ripping can often be short-lived in subsequent years on these soil types. The degree of mixing depends on the design of the ripper.
Incorporation of organic matter and gypsum in dispersive soils and minimising or avoiding re-compaction with a controlled traffic system, especially when these soils are wet, help maintain the soil structure and benefits of deep ripping.
Deep ripping of duplex soils can be beneficial when the sandy or loamy 'A-horizon' is shallower than the depth of ripping so clay soil can be mixed with sandy top soil increasing surface soil cation exchange capacity and reducing water repellence.
The cost is estimated at between $40-50/ha for deep ripping sandplain soils, much of it related to the draft force required to pull the deep working tines through the soil and the impact this has on fuel use and power requirements. This can be reduced by using a shallow leading tine ripper (Figure 1) which can reduce the draft force required to pull a deep ripper. A large time cost is usually associated with deep ripping. It is an additional operation often occurring near seeding and may compete with early sowing.
Deep ripping (deep tillage) involves the use of strong deep working tines that penetrate the compacted soil and mechanically break up and shatter the soil hard pan.
For deep ripping to be effective:
- The ripping tines must be able to penetrate just below the compacted soil layer
- Soil must be moist enough to allow penetration of the ripping tines but not so moist that the tines cause smearing without fracturing and shattering the soil.
Some firming of the soil surface by a roller or soil packer behind the deep ripper can be beneficial to avoid sowing too deep on soft, deep ripped soil. A roller or soil packer behind the deep ripper or attaching wings behind the tines can minimise the risk of a rough soil surface and soil softness causing uneven seeding depth and crop establishment.
Loosened soils can be more susceptible to compaction after deep ripping if not managed carefully. It is thus recommended to leave deep ripped soil to settle for at least two weeks before sowing.
Traditionally deep rippers rip the soil with tines all set to the same depth which have to penetrate and fracture the soil to full working depth. Research has shown, however, that single shallow leading tines working in-line and ahead of the deep ripping tine reduce the draft force by up to 18% with the leading tine working at 10cm on clay-textured soil.
On sandy-textured soils with the leading tine working at 10cm draft force is reduced by 10%. The shallow leading tines loosen the upper soil layers reducing the resistance and amount of soil the ripping tine has to fracture. Shallow leading tine rippers are also ideally suited to placing lime or other soil amendments at a range of depths into the soil profile behind the tines.
Timing involves finding the appropriate window for ripping when the soil is moist, whilst not conflicting with seeding. The options include:
- Deep rip after seeding but early enough not to disturb establishing plants too much (generally within three days of seeding) although this can also reduce crop establishment
- Deep rip in the inter-row of crops sown on wide rows during the growing season
- Deep rip opportunistically after significant out-of-season rains.
One of the largest potential downsides associated with deep ripping is that it increases the risk of haying off when soil water reserves are low and the finish to the season is dry. In some situations, faster water use and increased vegetative biomass caused by deep ripping can leave inadequate stored soil water for grain filling resulting in haying off and reduced yields.
|The risk of haying of is increased in:||The risk of haying off can be reduced by:|
|Dry seasons with a hot dry finish||Avoiding deep ripping in seasons predicted to be drier than average, particularly if there is no stored subsoil moisture at the start of the growing season.|
|Low rainfall areas/regions (less that 350mm)||Reducing early crop vigour by using wider rows, lower seeding rates, or reduced early nitrogen apllications.|
|Years when there is minimal subsoil moisture||Using shorter season crop varieties after deep ripping to account for the increased rate of subsoil moisture use.|
|High input systems with high levels of applied nitrogen driving increased crop vigour and large crop biomass||Using water efficient, low vegetative biomass varieties in the year the soil was deep ripped.|
|High soil nitrogen as a result of summer rainfall can also increase crop vigour and the risk of haying off, although higher subsoil moisture reserves could negate this||Deep working at seeding, resulting in only partial amelioration of compacted soils and avoiding the large vegetative biomass response generally observed after deep ripping.|
The science behind deep ripping
Where root growth is retarded or a greater amount of energy is required for roots to grow through compacted soil, production is usually reduced. After removing the compaction layer by deep ripping plant roots grow faster and deeper, increasing the amount of water and nutrients they can access, and as a result crop yield improves (Figure 2). The severity of the impact of subsurface compaction on root growth is dependent on many factors, primarily soil type and amount of compaction. In sandy textured soils, roots slowed by moderate compaction are less effective at keeping up with water and dissolved nutrients, particularly nitrogen, as they infiltrate through the soil profile.
Occasionally, under some seasonal conditions, when water deeper in the subsoil is not used as quickly due to the slow early root growth, more water is left available in the subsoil later in the season for grain filling, thereby delaying the onset of water stress and reducing haying off. In heavy textured soils severe compaction can restrict root growth to channels, cracks or softer parts of the soil and reduce the volume of soil available for root exploration.
Integrating compaction management with controlled traffic
General grower experience and on-farm trials indicate that:
Clay soils that have shrinking and swelling characteristics can repair themselves over time by the natural shrinking and swelling process that occurs as a result of rainfall patterns and improvements to soil health (especially the activity of earthworms, ants and termites) if wheeling is removed and confirmed to permanent traffic lanes.
Deep rippers and spaders can be modified to deep cultivate between permanent wheeltracks when or after a controlled traffic system has been established. Tines or spades are removed from the wheeltrack zone in the first pass and any uncultivated ground between the first passes is treated in a second pass with the tines or spades replaced and perhaps outside tines or spades removed to fit the width.