SP FAQ - The Influence of Cross Slot No-Tillage on Crop Yield
A significant amount of recent scientific research has been devoted to finding out exactly what influence a no-tillage drill can have on (1) stand establishment and (2) crop yield.
(a) No-tillage drill openers have a major influence on the micro-environment that seeds and seedlings experience in untilled soils (tillage tools, rather than drills, have most influence on the seed's micro-environment in tilled soils).
Good no-tillage seed drill openers create a seed micro-environment that is more favourable to seeds than any tilled soil has ever been. But sub-standard no-tillage seed drill openers create micro-environments that are more hostile to seeds and seedlings than tilled soil.
But the point is that no-tillage opener design can have a profound effect on slot micro-environment whereas in tillage, opener design has a minimal effect.
(b) This micro-environmental influence is itself largely determined by surface residues, particularly where they finish up relative to the slot (since there are no surface residues in tillage, they play virtually no role in tilled seedbeds).
Residues over the slot trap 90-100% moisture vapour within the slot (seeds will germinate in 90-100% relative humidity). Loose soil traps 60-80% (not enough for germination) and no cover allows free exchange with the atmosphere.
(c) Drill openers have a major influence on how seeds derive water for germination (imbibition). In no-tillage, vapour-phase water (or soil humidity) is an important germination resource whereas in tilled soils humidity usually plays a very minor role because of general soil loosening and loss of humidity to the atmosphere. Liquid-phase water is the main resource in tilled soils and highly-disturbed no-tillage slots.
(d) Similarly, no-tillage drill openers have an important influence on aeration around seeds and seedling roots in wet soils. Residues returned over the slot in wet soils draw earthworms to the slot zone since residues are the earthworms' main food source. The earthworms, in turn, aerate the slot zone, which has a measurably positive effect on germination and seedling survival in wet conditions.
By contrast, if no-tillage openers shift the residues away from the slot zone, the earthworms follow the residues to wherever they have been shifted to. Since there are no residues in tilled soils and earthworms are usually scarce anyway in tilled soils, none of this applies to tilled soils.
(e) Drill openers influence soil compaction around the seed. Compaction, in turn, can influence how well or poorly juvenile seedling roots develop (tillage eliminates most of the influence of openers on compaction by uniformly loosening the soil).
(f) With no-tillage, a slot wall is created between the slot zone and the soil alongside (in tilled soils, slot walls are indistinct since all of the soil has been disturbed anyway). If these no-tillage slot walls are nearly vertical (and even worse are compacted or at least smeared) they may restrict early root growth to the extent that in severe cases the roots never leave the slot zone and the crop performs poorly.
But if the no-tillage slot walls are near horizontal or indistinct, no such root restriction occurs.
(g) Certain no-tillage drill openers can have a negative effect on germination by pushing uncut straw into the slot (called 'tucking' or 'hairpinning' ). In anaerobic conditions especially, fermentation of the 'hairpinned' straw creates fatty acids (particularly acetic acid) that kill seeds and seedlings (the absence of residues in tilled soils avoids the problem altogether).
But better-designed no-tillage openers either do not push straw down into the seed slot at all or separate the seeds from any straw that is pushed in (10 mm or ½' separation is enough) thereby also avoiding the problem, even in heavy straw situations.
(h) The seed micro-environment is also influenced by depth of seeding. Consistency of depth is more important and difficult to maintain in no-tillage than in tillage and drill design has a major influence on how well this is achieved where it can have a major influence on crop yield (in tillage, because the soil is made uniformly soft and smooth, drills have a much simpler job to do in maintaining a consistent seedling depth).
(i) No-tillage drill openers influence how well drilled slots are closed. Covering is harder to achieve than in tilled soils because the soil is less friable. But inverted-T shaped slots are easier to cover than any form of vertical no-tillage slots. Covering, in turn, influences slot drying together with bird and insect damage.
(j) Post-drilling slot shrinkage occurs in most no-tillage slots when warm windy (drying) weather follows drilling in an otherwise damp 'plastic' soil. Most vertical (or near-vertical) no-tillage slots are likely to shrink open, exposing seeds. While the central slit in inverted-T shaped no-tillage slots may also shrink open, the seeds are deliberately tucked off to one side under the horizontal soil flaps and are therefore seldom, if ever, exposed.
The friable nature of tilled soils avoids post-drilling slot shrinkage problems altogether.
(k) Finally, seed drill openers determine if and where fertilizer is placed (banded) during the drilling process. Some no-tillage openers are capable of banding fertilizer (sometimes referred to as ' double shooting' ). Others are not (and this is referred to as 'single shooting' ).
Banded fertilizer during no-tillage can have a strongly positive influence on crop yield, especially with spring-sown crops. Not only does banded nitrogen replace soil nitrogen that may be temporarily locked up by micro-organisms while they decompose the surface residues, the alternative of surface applied (broadcast) fertilizer is often ineffective in no-tillage. This is because solutes from broadcast fertilizers tend to flow preferentially down bio-channels left by dead roots and earthworms in untilled soils and may largely bi-pass the juvenile roots of the new crop.
Even although tillage also destroys soil structure and fauna (which has long-term detrimental effects) in the short term, tillage mineralizes nitrogen already in the soil, making seedlings less dependent on banded fertilizer at seeding time than with no-tillage. Further, because tillage also destroys bio-channels and replaces them with a more-or-less uniform (and temporary) artificial pore system, broadcast solutes move more uniformly through tilled soils and are therefore more likely to reach juvenile roots than in no-tillage.
Of course soil, weather, genetic makeup, fertilizers, husbandry, and pests and diseases are fundamental determinants of crop yield. But even these fundamental resources are ineffective unless no-tillage drills are able to position seeds, seedlings and growing plants to take full advantage of the resources.
Another way of looking at it is that a poor no-tillage drill design can negate the positive effects offered by good soil, weather, genetics, fertilizers, and husbandry.
We hear repeatedly from farmers all over the world who have changed to Cross Slot no-tillage, that they are now getting their best-ever crop yields. But anecdotal evidence like this is difficult to quantify. So we have summarized some of the more noteworthy published longer term yield comparisons between Cross Slot no-tillage (CSTNT) and other methodologies: