The dry start to 2019 meant many growers didn't do any deep ripping, or started ripping and then stopped because they thought the soil was too dry or might blow.
But, come harvest, some crop yields were markedly better where they did rip dry, making growers wonder if they should have pushed on and whether they should be ripping now with an early finish to harvest and some spare labour.
Ripping some soils when they are dry can do a better job of shattering compacted subsoil - and topsoil slotting plates work well in drier conditions.
But ameliorating when it's too dry comes with extra costs and some pitfalls. It uses more fuel, puts extra wear and strain on machines and labour, and comes with a higher erosion risk from knocking over or uprooting stubble.
In some cases, working dry can cause more damage than good to both the hip pocket and the soil.
Is it too dry to rip soils?
The best way to find out is to put the machine in the ground and have a go. Some indicators that it is too dry are:
- tynes aren't getting down to the depth you need - this means knowing what depth is compacted before you start and checking the ripper has broken it up;
- you are pulling large soil clods to the surface, which ordinarily wouldn't happen;
- there is too much wheel slip;
- you are operating considerably slower and/or using more fuel than expected (e.g. if you normally work at six kilometres per hour and can only work at 2km/h, or if you typically use 100 litres per hour of fuel and you are using 150L/hour); or
- you are breaking tynes or wearing down points faster than expected (e.g. you expect a set of points to last 300 hectares but they wear out after 80ha).
It is important to gauge the cost of dry ripping and the likely benefit of it. Operating costs for DIY ripping are usually about $100/ha. If dry ripping, this can go to $150 to $200/ha, so you should be confident of a yield response.
It is also important to dig a pit behind the furrow and check the depth and quality of the rip. This small effort upfront is better than wasting money and weeks ameliorating when you should have stopped.
In lieu of a pit, dig some holes with a shovel and use a penetrometer or a sharp rod/stick to determine how deep you are ripping and confirm that you are shattering the compaction layer.
If you are not going deep enough you should stop ripping. But if you really want to push on, there are a few tricks to help the machine dig deeper.
You could try doing a double pass - a shallow rip followed by a deeper rip - although this is an expensive way to work.
Some rippers can do this in one pass with a shallow leading tyne, which can reduce draught by up to 10 per cent on sands and 18 per cent on 'clayey' soils.
Narrowing the ripping width by taking a tyne off each end of the machine helps tynes dig deeper within the tractor capacity. Another option is to increase tyne spacing and add winged points.
Wider spacing that gets below the hardpan is better than having more tynes 'pseudo ripping' above the hardpan. Removing the inclusion plates can also help.
Some growers simply add extra weight. This might keep the tynes down, but it burns more fuel and eventually something breaks.
If it is very dry, machinery adaptations might not have much of an impact, costs will still be high and the end result will be suboptimal. This is why it is critical to check the quality of the rip before persisting.
Dealing with clods
A big problem with dry ripping some soils is bringing clods about the size of house bricks to the surface.
Clods ultimately result in poor crop establishment and performance from a combination of factors, including:
- poor trafficability at seeding;
- uneven seedbed;
- variable seed depth; and
- preferred pathways for water infiltration and consequential concentration of pre-emergent herbicides - this can happen even if the clods are pushed/rolled in after ripping because the seeder drags them up again.
Trafficability, which is reduced after ripping, can be improved by ripping on a five-to-seven-degree angle to seeding.
Clods are not usually an issue in paler (even yellow), deeper sands (less than five per cent clay) without an obvious soil texture change within the ripping depth.
It is best to start dry ripping deep sands and sandy earths. If rain comes, other soil types could then be ripped.
Grain yield responses to deep ripping on the lighter soil types are more reliable, especially in areas with more than 350 millimetres of rainfall.
Clods tend to be more of a problem in more loamy sands (five to 10 per cent clay) and particularly in duplex soils. As a general rule, the redder the soil, the bigger the problem.
Packers or a roller can hide clods by pushing them into the soil. Take the roller/packers off while deciding whether to rip so clods are easier to see.
It is sometimes better to rip without a roller to maintain furrows and ground cover to reduce erosion, especially in a lupin, canola or poor cereal stubble.
If keeping the roller/packers on, check for subsurface clods while checking the quality of the rip. If you have subsurface clods, stop ripping.
Inverting the soil
The main risk of inverting or mixing dry soil in summer or early autumn is erosion. If you need to invert or mix dry, do it as late as possible.
The exception is mouldboard ploughing in gravels, where inverting is better done dry. But, again, do it as late as possible to minimise erosion.
Results from inverting/mixing when dry to incorporate surface-applied lime and/or to dilute surface non-wetting are variable.
Some growers gained an extra 0.5 to 0.7 tonnes/ha from a late March mix in 2019, while others think it lessened frost damage.
But there are some concerns around a dry invert/mix to be aware of in addition to the erosion risk, including:
- poor mix/invert - spaders and one-way ploughs work best when there is some moisture, otherwise subsoil won't hold on the spades/discs and may move to the surface;
- the benefit may not last as long - proper mixing should ameliorate water repellence for three to five years;
- insufficient mixing, especially in pale deep sands, only reduces repellence for a year or two; and
- it can make non-wetting worse by fluffing up the topsoil without diluting it with more wettable subsoil.
If possible, it is better to do a smaller area when the soil is wet prior to seeding, during seeding or at the end of seeding.
Some growers mix at the end of seeding, when the soil is more likely to be wet, knowing they may cop a yield penalty with late seeding, but get bigger benefits in subsequent years because they did it well.
A good option for pale deep sands is to rip dry and invert/mix later when there is suitable soil moisture.