SP FAQ - Hairpinning and Shading by Residues
The residue decomposes and in so doing creates acetic acid, which burns the seeds or seedlings, thus reducing emergence counts.
The central disc of Cross Slot openers will push residue down into the vertical slit under certain circumstance. There is no known disc opener that does not do this. The difference though, is that with Cross Slot openers the seed is placed off to one side of the vertical slit on a horizontal shelf. Seeds are never in contact with the residue. The acetic acid that is produced by decomposition of the residue is very rapidly broken down itself by soil microbes. Even a small amount of physical separation (as little as 10 mm) between the residue and the seed is effective in preventing seed burn. Only Cross Slot openers achieve this.
With all other openers (including slanted discs that produce angled slots) the seed is deposited right into the residue that is tucked into the slot. So seed burn is inevitable in those circumstance when and if acetic acid is produced as a result of decomposition.
Yes! When the soil is dry and the residue therefore does not readily decompose. But then the seed may be prevented from having good seed-soil contact because the residue insulates it from contact with the slot walls.
Even when such soils wet up, the hairpinned residues may absorb the moisture more quickly than the soil and begin decomposing about the same time the seeds are germinating.
So one way or another, unless the seed can be tucked off to one side of a slot created through heavy residue levels in no-tillage, it could be at risk in both dry and wet soils. The only time the risk does not exist with other openers is when soil moisture conditions are optimal and there is plenty of in-slot oxygen available, but no-one can guarantee that happening at any time, let alone all of the time.
Sometimes, yes. But seedlings that emerge from Cross Slot slots, even in optimum conditions, are thought by seed physiologists to be advantaged because of the relatively small amount of energy they expend and the lack of stress they encounter in getting to the soil surface. The high-humidity of Cross Slot slots is thought to have an important effect in cocooning the seedlings in a favourable atmosphere prior to emergence, and thereby influencing crop yield potential even before the seedlings have emerged from the soil, even when plant counts between Cross Slot and other openers are the same due to favourable conditions. But then seedling emergence is only one part of the equation anyway.
Yes. This can be both an advantage and a disadvantage. It is good in the autumn when the soil is drying and the climate is hot because it reduces the surface temperature of the soil and protects the soil from drying. It also reduces diurnal (day and night) fluctuations. It can also be a disadvantage in spring because it slows down the rate at which the soil heats up again after a cold winter.
Yes and no. Certainly, by replacing residues over the slot, soil temperatures are likely to rise more slowly in spring. A common remedy, regardless of opener type, is to use row cleaners (or 'residue managers' ) ahead of the openers to scrape the residues to one side (or both sides) of the row. This can be done as effectively with Cross Slot openers as with any other openers. But by doing so you loose the benefits of residues as the cover over the slot, which is unique to Cross Slot. But since moisture is seldom limiting in spring this is of no major consequence.
On the other hand, because the control of Cross Slot seeding depth and moisture retention is so good, seeding with Cross Slot openers can often take place at shallower depths than with other openers. The soil temperature at, say, 25 mm seeding depth under residues (as for Cross Slot operating without residue managers) is likely to be little different from the soil temperature at, say, 40 mm operating with residue managers.
To some extent therefore, the 'jury is still out' on this issue.