SP FAQ - Fertilizer placement (Banding)
Another major determinant of crop yield is how well the plants are fed and this is influenced by fertilizer placement at the time of sowing.
In a survey of no-tillage experts in the USA in the early 1990's, all agreed that the single most important feature they would like to see on no-tillage openers, was the ability to place (band) fertilizer separately at the time of seeding. Cross Slot openers provide a facility in this respect that no other design has yet emulated, let alone surpassed.
Cross Slot openers are unique in their ability to band fertilizer horizontally with the same opener that sows the seed
Some do. With some designs two openers are married together so one places seed and the other bands fertilizer, but the combined opener occupies so much space that this seriously limits how close the sown rows can be to one another on a drill. In other cases manufacturers provide two rows of seed and every third row is for fertilizer alone (known as 'skip row' ). This has a negative effect on crop yield but is better than broadcasting the fertilizer instead.
In still other designs (mainly hoe or shank-type openers and sweeps) separate fertilizer banding is achieved by creating a large disturbed zone with a tine and splitting the flow of seed and fertilizer before they reach the ground. But the amount of soil disturbance such openers create largely negates their claim to being no-tillage openers. They also have only a limited ability to avoid blockage with surface residues, which further prevents them from being used repeatedly in a true no-tillage environment.
The photograph below shows the disturbance created by a typical shank-type opener. This much soil disturbance is more correctly described as minimum tillage, even although it has been caused by a seeding machine.
Yes! Scientists in USA have shown that horizontal banding of seed and fertilizer under no-tillage produces superior crop yields compared with vertical banding. Cross Slot openers specialize in horizontal banding. But, in addition, by using optional short and long side blades on either side of the disc Cross Slot openers can also be made to produce diagonal (i.e. partly horizontal and partly vertical) banding for those who have come to believe that 'deep banding' is the only way.
One of the biggest mistakes no-tillage growers and machinery designers can make is to assume that what works in tillage will also work in no-tillage. Just because 'deep banding' (placing fertilizer up to 75 mm or 3 inches below the seed) seemed to work in tillage does not mean it works in an untilled soil. In fact there is strong evidence that such is not the case.
Because the US Department of Agriculture conducted extensive independent trials over a three year period comparing Cross Slot openers (horizontal banding of seed and fertilizer) with Yielder double disc openers ('deep banding' with vertical separation of seed and fertilizer in a skip-row configuration). In none of the seven separate experiments was the crop yield from the Yielder openers equal to (let alone superior to) that from Cross Slot openers. The average wheat yield advantage over 3 years in favour of Cross Slot openers was 13%.
Up until that time Yielder openers had produced the best crop yields of any no-tillage openers then available in the USA.
Because no-tilled soils behave differently than tilled soils when fertilizer is applied. Untilled soils contain earthworm and old root channels that the soluble nutrients run preferentially into, which means that much of the nutrients get diverted away from the small root zones of new plants sown in rows. In a tilled soil these channels are broken up by the tillage process and replaced by an evenly-dispersed artificial pore system. So fertilizer filters down more or less evenly in a tilled soil.
Thus it is more important to band fertilizer in no-tillage than in tillage. Very poor crop responses have been recorded from broadcasting fertilizer on the surface under no-tillage whereas good responses are commonly obtained doing the same thing on tilled soils. The differences have been greater in spring than autumn.
Typical differences with newly-sown pasture (left) and maize (right) attributable to banded fertilizer compared with broadcast fertilizer.
Because pastures contain a labyrinth of mature roots that intercept all fertilizer that is placed on the ground surface and is washed into the soil by rain, regardless of the presence or absence of earthworm and old root channels.
With phosphate, potassium, sulphur and micronutrients, use the same amounts that would be used in tillage. Feel confident about using micronutrients such as boron and elemental sulphur that can burn the seed if mixed with it. It will be separated from (and not burn) the seed with Cross Slot openers.
With nitrogen it is usual to increase the amount applied at sowing under no-tillage anyway, compared with tillage. This has nothing to do with opener design (except that it is not possible to apply any nitrogen at all with many other no-tillage openers). It is because under no-tillage generally, the soil microbes use a lot of nitrogen in decomposing the sprayed weeds and surface residues prior to seeding. This can result in the young crop becoming nitrogen deficient for a period. Banding nitrogen fertilizer at seeding overcomes the short-term deficiency, which ironically corrects itself later in the growth cycle anyway when the microbes themselves die and release the nitrogen again.
With tillage, nitrogen is mineralized by the tillage process, which (1) creates a convenient source of nitrogen for the young plants, but (2) is achieved by oxidizing some of the organic matter in the soil and eventually leads to reduced organic matter levels, which in turn leads to erosion and lower crop yields.
Sometimes yes! Other machines may be able to dispense fertilizer at the same time as seed but it is what happens to it in the soil that matters. Unless the openers are doubled up (as described above) some of this seed and fertilizer may become mixed together either before or as they enter the soil. Other openers (including Cross Slot) keep the two separate, including in the soil. This is called 'double shooting' . The tell-tale design difference is that if openers have separate product tubes for seed and fertilizer they will likely be capable of double shooting. But if they have only one tube going to the opener they will likely not be applying fertilizer at all or the two are being mixed together prior to entering the soil
A small amount of mixing is acceptable if the fertilizer rates are low and special slow-release forms are used (such as low rates of DAP), but normal fertilizer rates cannot be safely applied without the risk of 'seed burn' by the fertilizer.
The mixing problem is exacerbated by the absence of loose soil in many no-tillage slots, compared with tillage. Loose soil otherwise dilutes the fertilizer somewhat. It is also worse in dry soils than wet soils because in dry soils the fertilizer-solutions (as they dissolve) remain more concentrated and create an osmotic effect that draws water away from the seed rather than allows water to enter the seed.
Yes! One of the main features of the horizontal separation action is that it is equally effective in wet, dry and optimum soils and is unaffected by the presence or absence of surface residues or stones, and at forward speeds up to 10 miles/hour (16 kph).
No! Both ammonia as a gas and liquid fertilizers can be sown with Cross Slot openers at the same time as the seed with no detriment. In fact liquid or gaseous fertilizers can even be sown at the same time as dry fertilizers using Cross Slot openers.
To keep the wet or gaseous fertilizer from contacting the central disc (a wet disc is undesirable) the delivery tubes are angled away from the disc under the soil while dry fertilizer slides down beside the disc.
Approximately 20 mm or ¾ inch.
It is certainly closer than the deep banding that is recommended for tilled soils. But we are not dealing with tilled soils. We are dealing with untilled soils, which are different in many important ways. Scientists in Illinois, for example, showed that under no-tillage, corn yields started to decline for separation distances greater than 1 inch (25 mm) and after 2 inches (50 mm) the fertilizer had very little benefit at all.
They also showed that horizontal separation was superior to vertical separation in both avoiding seed 'burn' and getting maximum yield responses.
The liquid application tubes on Cross Slot openers are small diameter (3/16' and ¼' ). So long as a pressure of 30 psi can be maintained, the fertilizer will remain as a gas until it exits the tubes under the ground. No frosting of the tubes occurs and any frosting that occurs at the exit point of the tubes, is broken off by the soil passing by.
This is largely self-regulating. When there is little residue present, there is appreciable soil throw by Cross Slot openers and this is also speed dependent. Certainly, experience has shown that there is enough soil throw for application of triflurolin herbicide.
Where more residues are present, there is less soil throw but the mulching effect of the residues reduces the weed burden anyway and the need for a pre-plant-soil-incorporated herbicide therefore decreases.