Mechanically ameliorating soil by ripping, spading and ploughing chops up the soil surface and can leave holes, ruts, mounds and a rough surface. Bulldozing the soil (often caused by incorrect equipment set-up), bringing clods and rocks to the surface when ripping, and wheels and implements going off dedicated tracks can all make a lumpy paddock.
Uneven paddocks are rough on machines (and the operator) and lead to poor seeding depth control and uneven or patchy crop emergence. Harvesting is hard because the soil height - and the plants on it - vary across the header front and in the worst cases the header hits or picks up sand and rocks.
Levelling options
Paddock levelling options fall into six broad categories.
- Disc cultivators
e.g. Bednar Swifterdisc, K-Line Speedtiller®, Degelman Pro-Till®
These machines, designed primarily to break up clods and crusts on the surface and knock stubble over, provide some levelling. They operate relatively shallow, at about 10-15 cm, and are often used to help manage crop residue and incorporate lime into the topsoil.
These machines are a popular option after ploughing or spading. They will level the surface and providing they are set up right, won’t undo the amelioration. Most machines have rollers or packers on the back to firm the surface.
Some growers use the machines at an angle to amelioration to smooth the surface, however, this means more soil recompaction compared to sticking to dedicated tramlines. Working a touch slower and having some soil moisture present has anecdotally meant a better levelling job.
Because they only work the surface these machines won’t deal with large ruts or mounds. Working when the soil is too wet can create clods and smear the surface. Working dry soils or working too aggressively or too frequently can cause soil structure decline that can lead to soil stability issues during or after seeding or while soils remain bare in fallow.
- Levelling machines, land planes, grader boards
e.g. KB Rotacon Leveller, Ag Shield land leveller (roller with a levelling blade).
Land planes and levelling machines will make the most level surface (Figure 1) but come at the expense of soil compaction. These machines are great to level out old tracks, fill in holes and make a flat seed bed, but the operator usually needs to drive in multiple directions to drag the earth into holes and make a smooth surface. For instance, after ploughing a paddock it is common to drive up and back to smudge and level, then drive on a 30 or 45 degree angle to fix the plough furrows, then in the normal machinery direction once more.
Soil needs to flow across the blade of these machines so they do not cope well with stubble or rocks. Stubble can hook onto the edge of the blade and bulldoze the soil, resulting in more rather than less unevenness.
- Harrows
Spring tine or finger harrows are typically used in conjunction with cultivators, scarifiers, chisel ploughs or deep rippers. They are designed to break up clods and level the soil after cultivating/shallow ploughing - they can be useful after shallow tillage but will struggle to level deep furrows or deal with big clods.
Harrows are a ‘light touch’, moving less soil than other options but are still helpful.
- Chains
e.g. Kelly chain, Brookfield® chain, anchor chain
Chains are more useful for crop residue management, where only minor levelling is needed (for example, filling furrows and minor surface undulations rather than large ruts and bog marks) and to prepare the seed bed. They can provide some surface soil mixing and promote a flush of weed germination. An advantage is operators can cover large areas quickly.
The chain pieces come in a variety of sizes, weights and shapes, designed for various conditions. A prickle chain with angled rods works to level and pack soil and can incorporate pre-emergent herbicides. Spiked discs remove some weeds while preparing the seed bed. Dog-leg and knuckle chains are usually favoured in no-till but because there are flat rods that run parallel to the soil surface they can do a decent levelling job. Closer-spaced discs and discs with a deeper curve minimise the working depth in sandy soils.
Chains can be good, including in dry conditions, to bust up a hardened/crusted surface.
- Offset disc machines
e.g. Grizzly West Coaster
Offset disc machines are good for filling in larger ruts and are often used to incorporate residue and to mix in soil amelioration products such as lime and gypsum a bit deeper into the profile, making them both an amelioration tool and a useful leveller option after deep ripping or delving. Machines with bigger discs can cause a lot of soil movement for the result they deliver which can cause structural decline on some soil types with low organic matter or that are dispersive. They are more effective in moist soil and because they plough the soil, the paddock may need to be rolled afterwards.
- Tyned cultivators
These mainly older machines and their deeper working cousins (scarifiers) are a relatively effective levelling tool. They are commonly used to level ruts and run ends from one-way and mouldboard ploughing. Like many of the machines above, their effectiveness can be improved by using them on an angle to the amelioration option.
When to level
The best time to level means finding a balance between managing erosion risk, the right soil conditions to work in, and equipment and labour availability.
Levelling is not compatible with high stubble retention. More aggressive options break up and incorporate stubble. Less aggressive options such as land planes won’t work well with stubble present. Harrows and some chains work best when stubble retention is desired but will not do a good job on very uneven paddocks.
As such, levelling will leave paddocks exposed and at risk of erosion. One option is to level just before seeding, reducing the length of time soil is left exposed with low cover. As with other soil amelioration, working when there is some soil moisture is ideal; working too wet or too dry can make paddocks worse.
Most growers ameliorate, level and sow a crop in one season. Some ameliorate and sow a crop and put up with an unlevel paddock in the first year, then level it the next year after the soil has settled. This option can mean poor plant establishment in year one leading to a higher weed burden and erosion risk.
Ideally, avoid levelling when erosion risk is high. Wind or water erosion can quickly un-do the levelling work as the soil is soft and friable. The risk of erosion after levelling can be reduced by delaying rolling until just prior to seeding or using a ridged roller. Level smaller areas each year to reduce the area exposed to erosion risk.
Minimise paddock unevenness to start
Some amelioration operations like delving and ploughing that lift, mix or invert the soil make a highly uneven and soft surface that needs levelling and rolling afterwards. But options that move less soil, like ripping, when done right, can limit lumps and bumps.
Ripping at the right time and soil moisture and towing a weighted roller behind the ripper makes a decent surface. Ripping too dry can bring large clods to the surface, as well as doing a poor ripping job overall, being harder on machines and using more fuel.
Understanding soil type before renovating is essential to know what the renovation is likely to bring up - rocks, big clay clods etc., and to choose the right equipment and timing strategy. Using the right tool for the job reduces the need for extra leveling.
Undertaking mechanical amelioration on a fallow in spring can reduce the risk of erosion as soil cover levels are high, the soil is moist and the cultivated soil has time to settle over summer reducing erosion risk and providing a more even seed bed. The roller can be left off the ripper to keep stubble standing.
At the time of amelioration, if the surface is being left too uneven, adjust the machine accordingly or stop the operation. After amelioration, manage paddock traffic by sticking to tramlines where possible and adjust tyre pressures to suit the softer soils as this will reduce rutting and bogging that can create uneven paddocks.
For all options, doing amelioration right in the first place reduces the need to level the paddock.
Rolling
Options that level the paddock but leave a rough surface will also need rolling to establish a firm, even surface for seeding. They might also need a second cultivation if they are really cloddy as the roller could just push the clods back into the soil. A surface that looks level but not firm enough to drive on won’t stay level. Roll with a weighted roller to prevent wheel tracks sinking and mounding between the tramlines.
A crop has to be successfully established post amelioration and levelling so leaving a seed bed that will maintain stability and structure once furrows are implemented at planting is critical.
Acknowledgements: Bindi Isbister, Tim Boyes, Ty Fulwood.
This article was produced as part of the GRDC ‘Maintain the longevity of soils constraints investments and increase grower adoption through extension – western region’ investment (PLT1909-001SAX). This project is extending practical findings to grain growers from the five-year Soil Constraints – West suite of projects, conducted by the Department of Primary Industries and Regional Development (DPIRD), with GRDC investment.