Frequently Asked Questions about Cross Slot® Low Disturbance No-Tillage (LDNT)


1. Do the terms no-tillage, direct drilling, strip-tillage and minimum-tillage all mean the same thing?


No-tillage and direct drilling are essentially the same thing by two different names (we will use the term no-tillage in this document). Both are characterised by the fact that the soil has not undergone any form of tillage or cultivation before seeding and weeds have been killed or suppressed by non-disturbance means such as herbicide application, natural mortality or knife-rolling (otherwise known as crimping).

Strip tillage involves tilling relatively narrow strips of soil that the seeds are sown into while leaving wider strips untilled between the rows.

Minimum tillage involves light general tillage of the whole field before seeding. The technique is often used to reduce the severity of soil disturbance compared with ploughing while at the same time compensating for seed drills that do not work very well in undisturbed soil.

In some cases, minimum tillage may be a halfway step for farmers before they commit themselves fully to no-tillage, or until they have learned some of the new management skills required for no-tillage.

2. What is Low Disturbance No-tillage (LDNT)?

LDNT is a special form of no-tillage where the openers create the minimal amount of soil disturbance possible so as to minimize the amount of existing soil carbon that is oxidized to CO2 by the no-tillage openers and emitted into the atmosphere.

LDNT is also characterised by minimal disturbance of the surface residues during seeding so that the residues finish up in much the same position after seeding as they were in prior to seeding.

3. Why isn’t all no-tillage classified as Low Disturbance No Tillage?

Because most designers of no-tillage seed drill openers do not recognise the biological and carbon-conservation advantages of creating horizontal inverted T-shaped seed slots, which the best of the LDNT drills (i.e. Cross Slot®) create. Instead, competing brands (almost without exception) base their opener designs on one of two principles, both of which create vertical V-shaped or vertical U-shaped slots. These are:

(a) Shank-type (tined) openers, which maximise seed-to-soil contact by disturbing a lot of soil in the slot. This also allows the openers to band fertilizer separately from the seed. But shank-type openers get blocked in crop residues, so the residues therefore have to be disposed of pre-seeding. The excess soil disturbance in the sown row also oxidizes soil carbon at about the same rate as minimum tillage.

Typically, shank-type openers are used to undertake strip tillage.

(b) Or they design disc-type openers to avoid blockages with residues and to minimize soil disturbance. But in doing so, they often sacrifice reliable germination through poor seed-to-soil contact, create “undesirable hairpins in heavy residues, compact the slot walls, and are unable to band fertilizer at the same time as seeding. Despite these downsides, some disc-type openers can achieve LDNT.

4. How are Cross Slot® openers best described?

Cross Slot® openers are the pinnacle of Low Disturbance No-Tillage (LDNT) openers. They are sometimes regarded as a hybrid of both disc and shank type openers because they have both a single central disc and a pair of stationary winged side blades. They exhibit all of the good features of both disc and shank-type openers but have none of the limiting features of either. The slots they create are horizontal (inverted T-shaped) whereas both disc and shank type openers create vertical V or U-shaped slots that are difficult to cover or close.

5. How do the different openers and what they do affect soil carbon exchanges?

The openers micro-manage the way the slot is formed and covered.

All soil disturbance oxidises some of the existing soil carbon into CO? that escapes into the atmosphere. It is estimated that 20% of the CO? in the world’s atmosphere at any one time has come from the world tilling its arable soils each year to feed itself.

If the residues of previously harvested crops or purpose-grown cover crops (both of which contain about 40% carbon) are spread evenly across the field and are only minimally-disturbed by passage of the seeding openers, they will decompose over time and be taken into the soil by earthworms and other soil fauna. This is carbon recycling, sometimes referred to as carbon sequestration.

If more carbon is recycled into the soil from the residues than is lost from the soil to the atmosphere during the seeding process, the seeding process is said to be carbon-positive. But if the opposite occurs, it is said to be carbon-negative.

True LDNT is invariably carbon-positive.

High disturbance no-tillage or strip tillage is often carbon-neutral but seldom carbon positive. It may even be carbon negative, depending of the amount of soil disturbance caused by the openers, which itself is a function of forward speed and opener shape.

Minimum tillage is usually carbon negative.

Conventional tillage is always strongly carbon negative.

Because of the latter, ploughing straw or other organic matter into the ground is usually carbon negative or at best carbon neutral because more carbon is usually lost from the ploughing process than is gained from the buried straw.

6. Does LDNT affect the risks associated with no-tillage?

Yes. Strongly.

Not only does Cross Slot® LDNT recycle carbon back into the soil by micro-managing the crop residues properly, when a residue mulch covers the seed slot it traps soil water vapour in the slot that virtually guarantees seed germination and seedling emergence, even in adverse soil and weather conditions. This almost invariably translates into regeneration of soil health and increased crop yield.

7. Is LDNT compatible with straw burning?


LDNT depends on retaining all crop residues (including stubble and lose straw) as a source of recycled carbon while it also provides a moisture vapour trap for seedling establishment. Removing the straw altogether (by baling or burning) reduces the amount of available carbon for recycling.

LDNT can make the difference between crop success and failure. When a residue- mulch covers a sown slot (as is the case with inverted T-shaped slots created by Cross Slot® LDNT) 90 -100% relative humidity (equivalent to a thick fog) is trapped within the soil air that surrounds the seeds in the slots along with soil. This level of humidity is sufficient to germinate the seeds on its own, even in the absence of obvious liquid water.

The more residues the better.

8. Is organic farming compatible with LDNT?

Yes and no.

When organic farmers grow annual crops, they are not allowed to use inorganic herbicides to kill weeds. Some organic farmers therefore rely on conventional tillage to kill weeds. But tillage is the most inorganic thing anyone can do to soil.

If organic farmers can control weeds with either organic herbicides or use mechanical means that leave the dead weeds in situ on the surface of the ground (such as knife rollers) and then use LDNT to sow the new crops through the dead weed mulch, they will fulfil all of the objectives of true organic farming admirably. More and more organic farmers are doing exactly this.

9. Is it true that tilled soils absorb more water when it rains?


Unless the tilled soil is left in a cloddy state, medium-to-long-term water infiltration into tilled soils is less than into untilled, residue-covered soils. This is largely because of the splash effect on the surface of tilled soils that dislodges small particles, which seal the pores, restricting further water entry. Eventually, this leads to surface run-off, which carries soil particles and chemicals away, resulting in waterway pollution and siltation as well as erosion.

In no-tillage, if residues are retained they protect the soil from the splash effect and slow movement of water that would otherwise run off. LDNT also ensures that soil erosion does not occur within the sown rows themselves, which can otherwise occur with high disturbance no-tillage or strip tillage, especially where seeding has taken place up and down (rather than across) slopes.

10. How do Cross Slot® openers perform in wet and/or damp clay soils?

Unless the soils are very sticky, they perform much better than either shank-type or pure disc-type no-tillage openers. The horizontal shelves that the seeds come to rest on in the inverted T-shaped slots of LDNT are easily covered by folding back the slices of soil and residues that the wings of the Cross Slot® openers have undercut as they moved through the soil. By contrast, almost all other slot shapes are vertical (some are slightly angled) and there is very little loose soil available in damp conditions to cover vertical slots.

Further, both disc and shank-type openers will likely cause smearing within the slots. If these smears are allowed to dry through lack of cover they become crusts that severely restrict seedling root growth. The horizontal shelves of Cross Slot® LDNT slots never dry, so any smearing they create is of no consequence.

11. How do Cross Slot® and other openers perform in stony ground?

There are three considerations:

• How many stones are there in relation to the soil (e.g. are there stones amongst the soil or is there soil amongst the stones?)

• Are the surface stones too big to pass between the openers?

• How well do the openers cope with buried stones or reefs?

If there are stones amongst the soil, many (although not all) openers will cope with them. But soil amongst the stones may be another matter. Cross Slot® openers in 150 mm (6 inch) row spacing will cope well with a 50:50 mix of stones and soil.

Surface stones that are too big to pass through between the openers will stop any drill if the openers are closely spaced. Choose a drill with two or more tool bars or with widely spaced openers (longitudinally as well as laterally).

Hoe or tine-type openers often rip buried stones out of the ground and leave them on the surface and mechanical breakages are a real possibility. Most disc-type openers will ride over buried stones although breakages of lighter designs are still a risk.

If Cross Slot® LDNT openers are used, the central vertical disc hammers most surface stones progressively into the ground and seldom brings any new stones up onto the surface. And because the central disc runs straight ahead, is easily rides over stones that cause breakage with angled discs.

12. How smooth do fields need to be for Cross Slot® LDNT?

Because there is no opportunity to smooth untilled soils, Cross Slot® LDNT openers are provided with 400 mm (18”) of vertical opener travel in the soil, which is considerably more than almost any other known no-tillage opener. To achieve this, each opener is pushed into the ground with its own hydraulic cylinder connected to a nitrogen-cushioned accumulator system. There are no springs, so the hydraulic downforce remains constant throughout the full range of opener travel. The same cylinder also raises each opener for transport, which simplifies drill design.

Cross Slot® also invented the original Automatic DownForce (ADF) system in 1993 to work in harmony with this extended travel range. The ADF system senses how much downforce is required to maintain a consistent seeding depth even although most soils vary in hardness on a metre-by-metre basis. The ADF adjusts the oil pressure 3 times per second (equivalent to about 1 metre or yard of forward travel) to match the changing soil resistance and thereby maintain consistent seeding depth.

13. Do the large tractors and machines used in no-tillage compact the ground?

Not if the vehicles are equipped with large flotation tyres. Footprint pressures are usually kept to a minimum and some operators use tracked vehicles. Besides, when seeding, most of the weight of the seeding machine is carried by the openers and untilled soils have a much greater weight-bearing capacity than tilled soils anyway.

14. Is it true that untilled soils are slower to warm in the spring, and if so what are the implications?


The implications are that when no-tilling temperature-sensitive species the operators of many no-tillage machines may either have to wait a little longer in the spring for soil temperatures to rise, or remove the residues from over the row.

Removing residues conflicts with one of the advantages of Cross Slot® LDNT, which is to trap water vapour in the seed slot. But because seeds seldom need to be sown as deeply in LDNT soils as in tilled soils or even strip-tilled no-tillage slots, they can be placed closer to the surface where the soil is warmer anyway, even with resides covering the seeds.

The use or row cleaners to remove residues from the seed area during no-tillage so that seed-zone warming can take place more rapidly, is therefore usually not required with LDNT.

15. Are crop root systems restricted in untilled ground?

Possibly if a historical hard pan had developed from repeat tillage of the soil and/or soil structure had been destroyed. Soil structure is created by exudation of glue like substances by soil microbes. The energy sources for microbes are soil carbon (soil organic matter) and soil humidity. Repeat tillage lowers the carbon content of tilled soils cumulatively and this allows hard pans to develop.

But LDNT helps nature repair the damage so long as the seeding process is carbon positive. Over time, many soils that have been subjected to repeat LDNT have halved the horsepower required to pull the LDNT seeding machine through them due to this regeneration of soil health.

16. Are there any crops that cannot be no-tilled?

With Cross Slot® LDNT, we have yet to come across a species that does not respond positively to the biological superiority of the Cross Slot® system. Some fields have been double cropped by Cross Slot® LDNT for 20 successive years with no fallows at any time and no discernible ill effects.

17. Is it necessary to increase seeding rates with any form of no-tillage?

With inferior no-tillage machines, often yes.

But with Cross Slot® LDNT, quite the reverse is true. In many cases, Cross Slot® users have been able to lower their seeding rates by 10-300%*

*For example, in Western Australia, OSR seeding rates were lowered from 9 kg/ha under cultivation, to 3 kg/ha with Cross Slot® LDNT, and the resulting crops yielded more than the tillage crops had been doing anyway.

18. How does LDNT interact with soil microbes?

Beneficial symbiotic fungi like mycorrhiza thrive under LDNT and can have a direct positive effect on crop yield.

The prediction that certain pathogens and pests would thrive in no-tillage crop residues has proven to be unfounded. And soil biologists are now discovering and culturing microbes that are the predators of several common soil pathogens and diseases. This has the potential to greatly reduce agriculture’s dependence on synthesised pesticides but works best in association with LDNT because the natural habitat of all soil microbes is the 100% relative humidity contained in the pore spaces between soil particles, which is a defining characteristic of Cross Slot® LDNT.

19. Is there anything special about how fertilizer is applied during no-tillage?


On several fronts.

• Firstly, strip tillage may disturb sufficient soil in the slot zone to mineralize some nitrogen from soil close to the seeds. LDNT mineralizes less nitrogen than these more soil-disruptive practices. Seedlings emerging from LDNT slots therefore sometimes look less vigorous than in strip tillage for this reason. The same effect is sometimes seen where a tractor pulling a LDNT seeding machine experiences more wheel slip in one portion of a field than in other portions of the same field. The soil disturbed by the wheels slippage also mineralizes nitrogen that gives a short term boost to those seeds that emerge from the openers that passed through the wheel slip area.

The effect is short-lived and easily countered when undertaking LDNT by sowing a small amount of nitrogenous starter fertilizer with the Cross Slot® LDNT openers at the time of seeding.

• Secondly, it has become commonplace for farmers to expect to get a response to broadcast fertilizers when crops are sown into fully tilled or minimum tilled seedbeds. But the same responses do not necessarily occur when using any form of no-tillage, including LDNT.

The reasons are:

(a) If weeds have been killed prior to seeding, there will be competition for nitrogen between the decomposition microbes and the newly emerging seedlings, and

(b) Soluble nutrients may flow preferentially from the surface of the soil down undisturbed earthworm or old root channels in untilled soils and thereby bi- pass many of the newly sown root systems. In tilled soils, such preferential- flow channels are destroyed by the tillage process and the nutrients then disperse more or less evenly down through the soil profile and feed all roots on the way.

For both reasons, no-tilled seedlings respond much more readily to fertilizers that are banded alongside the seed by the seeding openers than in tilled soils.

But not all no-tillage openers can band fertilizer at the same time as they sow seeds. Most pure disc-type openers, for example cannot do this.

Most shank-type openers and all Cross Slot® LDNT openers can band fertilizer.

20. Is “deep banding” of fertilizer appropriate in no-tillage?

In the main, no! It is very unwise to assume that what works in tillage will also work in no-tillage. Deep banding in tilled soils involves separation distances (between seed and fertilizer) of 50-75 mm (2 – 3 inches). But in no-tillage, separation distances should be no greater than 25 mm (1 inch) but may be horizontal, vertical or diagonal

21. Does no-tillage require more fertiliser?


About the same as tillage.

22. Is LDNT cost-effective compared with other forms of no-tillage?


It only takes a 1-3% increase in crop yield to make LDNT (which uses more sophisticated machines) cost effective compared with other cheaper forms of no-tillage. And yield increases of 10 -15% have been common.

23. How much time, fuel, tractor –hours and labour are saved with no-tillage?


24. Is choosing between no-tillage machines, a matter of “horses for courses”?

Most farms have several different soil types and the way that each of these soil types behaves may vary from day to day with rain etc. No-one can afford to have several machines on hand to suit the different conditions. Therefore one of the most important features of any no-tillage machine is to be adaptable to a wide variety of conditions with minimum adjustment required when going from one condition to another. The ability to do this is one of the strongest points about how Cross Slot® LDNT openers operate.