Efficacy and cost of incorporating lime
The efficacy with which various implements can incorporate surface applied lime depends on numerous factors including:
- Soil type, in particular clay content, which can affect the cohesion, fracturing and flow of the soil.
- Soil moisture conditions - in sandplain soils moisture can help the sand maintain its form (greater cohesion) allowing slots to remain open for longer but may reduce fracturing and soil flow. Wetter soils are softer so this can improve the penetration of soil by implements and reduce draft. Dry surface sand flows easier when worked (less cohesion) which can be an advantage for moving limed topsoil behind soil openers. Optimal movement probably occurs when there is some subsoil moisture but the limed topsoil is dry and can readily flow into the fractured subsoil.
- Implement type - variations between machinery brands such as width of tines, curved or laid-back tines which may promote a lifting (delving) action; curvature (dish depth) of discs are just some examples.
- Implement set up and use - for disc ploughs and mouldboard ploughs setup greatly influences the incorporation result. Having ploughs more open will increase the work rate and the space between ploughshares available for soil to move but may limit the working depth.
- Speed of operation - higher speeds can result in more soil throw and mixing but may require a shallower working depth.
The table below gives a brief description of various tillage implements, the mixing action of each implement, typical working depth and some supplementary information on the efficacy of lime incorporation. Note that every situation is different and this information is designed to be used simply as a guide when considering options for incorporating lime.
| Incorporation implement (approx. cost range $/ha) | Overview of tillage action by implement | Typical working depth (cm) | Depth of lime incorporation achieved (cm) | Lateral spread of lime and incorporation efficacy *Images with purple soil are from application of universal pH indicator to identify placement of lime within the soil profile |
|---|---|---|---|---|
| Deep ripping ($45-55/ha)
 A standard deep ripper used to break out compacted subsoil | Narrow strong deep working tines used to break out subsoil compaction | 30-40 | 10-15, variable | Limed topsoil tends to be mixed in the surface layer where the tine passes through but generally the slot behind the tine closes rapidly so there is little opportunity for limed topsoil to fall deeper into the subsoil
 Root proliferation in a rip line. Although limed topsoil is often mixed in the surface layer, there is variable movement of lime down the profile |
| Shallow leading tine ripping ($40-50/ha)
 This shallow leading tine ripper has four sets of tines and is typically used for research purposes. Commerical shallow leading tine rippers have two sets of tines which rip at 20-30cm and then again at 30-50/60cm in the same pass | Ripping with shallow leading tines allowing deeper break out by deeper working, trailing tines | 40-50 | 10-15 | Limed topsoil can be incorporated better due to multiple tines disturbing the soil in the one pass, although incorporation is still limited as tines are narrow and slots close rapidly behind the tines
 A yellow sand deep ripped to 500 mm with a shallow leading tyne ripper |
| Shallow leading tine ripper with topsoil inclusion plates ($40-55/ha)
 Topsoil inclusion plate fitted to the rear tine of a shallow leading tine ripper | The addition of topsoil inclusion plates to the rear tines allows for the movement of topsoil rich in organic matter to depth | 40-50 | 30-40 | The topsoil inclusion plates keep the slot behind the rear ripping tines open for limed topsoil to fall into the subsoil. The result is vertical seems of organic matter rich/limed topsoil behind placed to depth behind the rear ripping tines
 Seems of topsoil with good pH placed to depth through the use of topsoil inclusion plates |
| Ripper with wings ($45-55/ha)
 A ripping tine with wings allows for greater soil disturbance as it operates below the soil surface and tends to lift subsurface soil | Wings mounted on ripper tines that operate below the soil surface when ripping which creates greater soil disturbance as they tend to lift subsurface soil | 30-40 | 20-25 | Limed topsoil can flow into the space opened up via the lifting (delving) action of the wings. Lateral incorporation is improved with 'tongues' of topsoil up to 8cm wide on either side of the ripping tine where the wings had passed |
| Ripper with 'Horwood' opener ($45-55/ha)
 Ripping tine with a 'Horwood attachment' to hold open the soil slot longer and allow limed topsoil to drop into the subsoi | Plates extend behind the ripping tine to hold open the soil slot longer operating just below the topsoil | 30-40 | 20-26 | Holding the slot open for longer below the soil surface allows limed topsoil to drop into the subsoil. A continuous stream of limed topsoil was achieved but the slot narrowed with depth being only 1-2cm wide at depth |
| Ripper with 'Railway Fishplate' opener ($50-60/ha)
 A 'railway fishplate' opener is essentially a plate bolted onto the side of the ripping tine to increase the level of soil disturbance | Plates bolted onto the side of the ripping tines effectively increasing the tine width and the degree of soil disturbance | 30-40 | 19-23 | More disturbance resulted in more mixing. Width of mixing was increased up to 14 cm in some instances but this was variable |
| Deep digger® ($60-70/ha?)
 The wide curved tines of the Deep Digger® are capable of ripping deeper than standard deep rippers | Large wide curved tines in a V-shaped arrangement capable of ripping deeper than standard deep rippers | 40-60 | 23-25 | Wider tines and some delving action allows some topsoil flow around and behind the tines but overall incorporation is fairly minimal for the cost. Tines would need to be modified to achieve better incorporation
 Incorporation of lime to a depth of approximately 25cm in West Binnu using the Deep Digger. The loose soil has been subsequently compacted by traffic |
| Offsets ($40/ha)
 A standard set of offset discs that cultivate the topsoil | Standard offset (two-way) discs that cultivate the topsoil | 10-15 | 10-15 | Very little limed topsoil is incorporated into the subsoil layers due to inadeqaute working depth. Mixing will still improve the reaction of the lime in the topsoil that may then allow for faster lime movement into the subsoil
 Incorporation of lime to 10-15cm in a yellow sandplain soil in Carnamah using offset discs |
| Large offsets ($50-60/ha)
 Large offset discs can cultivate to a greater working depth than standard offsets | Large offsets (two-way) discs, typically greater than 70cm in diameter, that can cultivate deeper than standard offsets | 24-25 | 24-25 | Limed topsoil is effectively incorporated to the working depth. Some layering occurs on an angle from the surface but generally the mixing is good. Visually it appears about two-thirds to three-quarters of the profile is treated to the working depth. The incorporation depth can be less if hardpans or gravel layers prevent disc penetration |
| One-way plough ($30-40/ha)
 A small one-way plough used for research trials | Discs throw the soil one-way, can achieve partial turning of the soil but mixing occurs as soil tumbles off the disc | 15-25 | 15-25 | Limed topsoil is partially mixed and layered on an angle from the surface because of the cultivation process. Despite partial inversion and layering continuous pathways of limed topsoil are still available for root growth. About half to two-thirds of the topsoil is buried. Can bring acidic subsoil to the surface so more surface lime may be required post-ploughing. |
| Rotary spader ($120-150/ha)
 A rotary spader used to bury some topsoil and lift up some subsoil | Rotating spades bury some topsoil while lifting up some subsoil. About two thirds of the topsoil is buried below 10 cm. Soil tends to take on a marbled apperance | 28-35 | 28-35 | Very effective at mixing limed topsoil into the subsoil. Does lift some acidic subsoil to the surface so additional lime may be required in subsequent years. Because spades are offset and overlapping lime is incorporated through the entire profile to the working depth, although pockets of acidic subsoil may remain.
 A soil profile of a yellow sand in Carnamah after spading. The spader thoroughly mixed the top soil and subsurface soil throughout the profile, bringing acid soil to the surface and burying the top soil and lime  Soil profile at a trial site showing buried topsoil in spaded treatment. The rotary spader has buried some of the topsoil to depth of 25cm but also lifted some pockets or seams of subsoil into the top 10cm of soil |
| Mouldboard plough ($100-150/ha)
 Growers will often topdress lime after mouldboard ploughing and bringing acidic subsoil to the surface | Curved mouldboard shares lift, roll and invert the soil aided by skimmers that scalp the topsoil into the base of the furrow. Square ploughs achieve a similar result | 28-35 | 28-35 | Inversion buries limed topsoil in a layer and can bring a thick layer of acidic subsoil to the surface that needs treating with more surface-applied lime. Continuous ameliorated pathways are not always present if inversion has been effective.
 A mouldboarded soil profile showing acidic soil brought to the surface and limed topsoil buried at depth after complete inversion. Additional lime has then been topdressed (stained purple from universal pH indicator) but there is no preferntial pathway of good pH to allow for root growth between the two layers  In this example in Carnamah, an incomplete soil iversion after mouldboard ploughing resulted in seams of limed topsoil alongside acidic subsurface soil |
| TopDown® plough (>$100/ha?)
 A Topdown® plough has a combination of leading offset discs then curved ripping tines, levelling discs and packers | A cominbination of leading offset discs then curved ripping tines, levelling discs and packers | 20-35 | 20-25 | Off set mixed well through to their working depth. Curved ripping tines then open a slot allowing surface soil to fall into 20-25 cm. This incorporation is a broad 'V' shape beginning at the width of the tine at the surface and finishing to a point at 20-25cm. Thr curved tines also lift acidic sub surface soils to the surface in seams. Not as effective in gravelly soils or soils with hard pans or layers that are difficult to penetrate
 The TopDown plough achieved lime incorporation to 28cm in Carnamah, incorporating lime in large V shaped patterns as subsurface soil is dragged to the surface either side of the tyne |