Q. It is difficult to believe that drills can influence crop yield. Surely it’s the weather, genetics, fertilizers, diseases, pests and crop husbandry that do that?
A. A huge 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) Drill openers have a big 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).
(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).
(c) Residues also provide the main food source for soil micro-organisms, which in turn create soil structure, and there is a direct relationship between soil structure and crop yield. Tillage destroys soil structure cumulatively. No-tillage builds soil structure cumulatively.
(d) Drill openers have a major influence on how seeds derive water for germination (imbibition). In no-tillage, vapour-phase water (or soil humidity) becomes an important germination resource whereas in tillage soil 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.
(e) Similarly no-tillage drill openers have an important influence on aeration around seed and seedling roots in wet soils (tillage does this instead in conventional seedbeds).
(f) 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 (in tillage, because the soil is made uniformly soft and smooth, drills have a much simpler job to do).
(g) Drill openers influence compaction around the seed. Compaction, in turn, can influence how well or poorly seedling roots develop (tillage eliminates most of the influence of openers on compaction by uniformly loosening the soil).
(h) Drill openers influence how well drilled slots are closed in untilled soils (covering is harder to achieve than in tilled soils because the soil is less friable). Covering influences slot drying together with bird and insect damage.
(i) Finally, seed drill openers determine if and where fertilizer is placed during the drilling process (fertilizer placement is not nearly as important in tillage as it is in no-tillage where it can have a major influence on crop yield).
Of course weather, genetic makeup, fertilizers, husbandry, and pests and diseases are the major primary determinants of yield. But even these fundamental resources are useless unless drills position seeds, seedlings and growing plants to take full advantage of them. Another way of looking at it is that a poor drill design can negate the positive things that good weather, genetics, fertilizers, and husbandry may offer.
Q. What is so special about controlling the seed micro-environment? Isn’t getting good seed-soil contact enough?
A. In short, no! Seed-soil contact is often not enough under no-tillage and is why no-tillage often fails compared with tillage. On the other hand it is also why no-tillage, undertaken with Cross Slot openers can be more failsafe than tillage.
Q. Does this mean soil-seed contact plays no part at all with no-tillage?
A. On the contrary! Seeds will take up water in both liquid and vapour (humidity) forms. Seed-soil contact is still important to maximize the liquid uptake, but the availability of vapour moisture in Cross Slot slots gives no-tilled soils an added resource to germinate seeds, which is why germination and emergence failures with Cross Slot openers are very rare events indeed.
Q. Does this mean that seeds sown with Cross Slot openers do not actually have to be in contact with wet soil?
A. Yes! It means exactly that. Provided there is a good mulch cover of surface residues it is not necessary to actually place the seed in damp soil. Close to it will be sufficient for the humidity to do the rest.
Q. In such circumstances will germination be as fast as if the seed had been in damp soil?
A. No! Relying on humidity alone (or even as the predominant mechanism) for germination will certainly delay germination since uptake of vapour water by seeds is slower than uptake of liquid water. But it will occur nonetheless.
Q. Don’t tilled soils also have such soil humidity?
A. No! The tillage process aerates the soil so much that soil humidity escapes to the atmosphere and finds a new lower level that seldom approaches even 90% (let alone 100%) except when it rains. Seeds sown into tilled soils therefore mostly rely on absorbing liquid water from the soil and this is influenced greatly by soil-seed contact.
Further, tillage destroys the natural capillary channels in soil that facilitate upward movement of liquid water as the soil surface dries.
Q. If that is the case why is no-tillage not always better than tillage?
A. Because not all no-tillage openers (and the soil slots they create) are capable of harnessing the soil’s humidity. Nor are many of them capable of even creating good soil-seed contact. Many aim to disturb the soil in the slot zone on the assumption that disturbance is somehow good. Although disturbance may assist seed-to-soil contact it breaks the capillary channels close to the seed and ensures that soil humidity escapes from the slot zone.
Q. How do we know this is not just all sales talk?
A. Because it is has been the subject of numerous scientific studies that are reported in the international scientific literature and were subjected to peer review by other international scientists over a period of 30 years. No-one has ever challenged these findings, which are also the subject of an international textbook on the interactions between soils, seeds and no-tillage openers (see below). Indeed, other scientists have supported them.
Q. Even although it would seem to be impractical, could you get the same effect from vertical slots by placing strips of say plastic over them?
A. Scientists tried this. Even although they found that the slot atmosphere did indeed remain at around 100% relative humidity, they also found fungal growth in the anaerobic atmosphere of the plastic-covered slots. From this they concluded that by ensuring soil gets covered with dead plant residues, nature has always provided a medium that retains moisture vapour but also lets the soil breath. Plastic cannot duplicate both functions. Cross Slot slots simply duplicate what nature has always done, so it is no surprise that seeds and plants respond favourably.
It is not an accident that most trees flower and then drop their seeds on the ground before they shed their leaves. The leaves then land on top of the seeds and create conditions similar to that created by Cross Slot no-tillage openers. All we are doing is duplicating nature except that we are choosing the seed type we want and putting it in rows.
Q. What happens to the slot micro-environment if dry soil comes into contact with the seed?
A. With some angled disc openers dry soil can fall into the slot before the seed, which effectively embeds the seed in dry soil. This cannot happen with Cross Slot openers since the seed travels down the inside of the blades, which prevent other soil from falling into the slot until after the seed has been placed. Even if some dry soil did eventually fall into Cross Slot slots the high humidity still ensures that germination will take place.
With other openers the dry soil cushion prevents the seed from getting access to liquid-phase water
Q. Is there a limit to the dryness of the soil from which seeds sown by Cross Slot no-tillage will fail to emerge?
A. Yes! But it is remarkable just how dry a soil they will tolerate. Scientists have recorded 50% emergence of wheat seedlings from a no-tillage soil sown by Cross Slot openers at –12 bar moisture tension. Moisture tension is a measure of how tightly moisture is held by the soil particles. A high negative moisture tension means that the soil is drier than at a low moisture tension. Minus 15 bar moisture tension usually defines “permanent wilting point”, which is where the soil is so dry that growing plants will wilt and not recover even if water is re-applied. Minus 12 bar is therefore close to “permanent wilting point”.
Q. Does that mean then that untilled soils have more potential to stimulate germination and seedling emergence than they have to sustain plant growth?
A. Yes! It means exactly that. Even at “permanent wilting point” an untilled soil will provide an equilibrium relative humidity of 99.8% in its pore space and this is the key to seed germination and seedling survival in such soils provided the no-tillage openers are designed to harness that potential. But a growing plant cannot harvest water at such a high tension. Experiments have shown that while you can get wheat seedlings to emerge from a soil at –12 bar the plants died soon after emerging.
Because tilled soils almost never have an equilibrium relative humidity approaching 100% (except when it is actually raining), germination must wait until there is sufficient liquid water for the seeds to absorb and this also ensures there is sufficient water for the seedling roots to sustain the plant both before and after emergence.
Q. Is there therefore a danger that Cross Slot openers will force germination from soils that are too dry for the plants to grow in?
A. That could be argued. But the solution (to redesign Cross Slot openers so they are less capable of germinating seeds) seems illogical. In reality it is very seldom that crops fail when sown with Cross Slot openers into untilled, residue-covered soils. In fact their ability to tolerate a much wider range of conditions than other openers is one of the main things that make them superior to all other no-tillage openers and gives them such a high failsafeness rating (99%).
Q. Are there advantages of Cross Slot openers in wet soils?
A. Yes! They are equally tolerant of wet soils for entirely different reasons (than for dry soils). And there are further advantages too.
Q. In what way are Cross Slot openers superior to other openers in wet soils?
A. Scientists have shown that when an inverted “T” (or horizontal) shaped slot is created in a wet soil, the placement of crop residue over the slot provides a ready source of food for earthworms, which actively colonise the slot zone. This in turn leads to an increased oxygen supply to the seeds because of their tunnelling. Further the tunnelling also increases the rate of infiltration of rain (or irrigation) water into deeper layers of the soil.
Double and triple disc openers create a compacted zone of low oxygen soil around the seed. Cross Slot openers retain high oxygen soil close to the seed.
Q. What opener types are worst in wet soils?
A. Double (or triple) disc type openers, because of their wedging action, produce sidewall compaction, which discourages earthworms from colonizing the slot zone. Further, by compacting the soil they exclude oxygen and push residue down into the slot allowing seed to become lodged in this residue.
The latter problem is known as hairpinning (because the straw gets bent over like a hairpin) and is explained in the section on surface residues.
Q. Does the placement of fertilizer influence crop yield potential?
A. 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.
Q. Is there anything else special about how Cross Slot openers band fertilizer?
A. Yes! Scientists in USA have shown that horizontal banding of seed and fertilizer under no-tillage produces superior crop yields to vertical banding. Cross Slot openers specialize in horizontal banding. 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.
Q. Given that you can place fertilizer in separate bands with Cross Slot openers, should growers be using more or less fertilizer when they no-till with these openers?
A. 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.
North Dakota State University (NDSU) scientists are now recommending that crop fertilizer N inputs should be increased by 20 lb N/ac (20 kg N/ha) for the first 5 years in no-tillage (compared with N required under conventional tillage) but can be reduced by 50 lb N/ac (50 kg N/ha) after 5 years of continuous no-tillage (compared with N required under conventional tillage).
Q. What is unique about the way Cross Slot openers close the slot?
A. An important function of no-tillage openers is controlling closure of the slot and also seeding depth. With Cross Slot openers both of these functions are undertaken simultaneously by the press wheels. They are located close to the seeding zone so they ensure the openers rise and fall (up to 45 cm or 18 inches if necessary) in harmony with changes in the soil surface.
But they also fold the soil flaps back over the seed so as to retain the integrity of a truly horizontal (inverted “T” shaped) slot with all of its advantages discussed elsewhere.