Sowing methods for direct seeding
In the last issue of terraHORSCH, Michael Horsch in this article “The fine art of direct seeding“ talked about direct seeding as a water-saving method, catch crop cultivation with direct seeding, what effect a covered soil can have and what direct seeding could be like in the future.
In this follow-up article Michael Horsch among others explains where which sowing method fits best, how it is used, and which preparations are required. The focus will be on the disc and tine technology.
Which technology fits where?
“From our past we have a lot of experience with tine systems for direct seeding“, Michael Horsch summarises. The Airseeder technololgy and then the Sprinter line with the different tools have always been optimised and adapted further over the years. Today, they offer a lot of options – from direct seeding with only little disturbance of the soil to an almost all-over work.
Tine technology is used for example in regions where farmers want to sow immediately after the harvest in fresh residues of the previous crop, for example rape or catch crops. The seed tine has a clearing character and leaves a clean seed furrow for a good soil contact of the seed.
Another significant advantage in cold regions is the somewhat faster heating of the soil. “For example, in Kazakhstan (trend towards small tines and sowing into the open furrow) farmers very successfully sow with the Sprinter NT. The tine clears the soil and leaves an almost black surface which can heat up faster and guarantees a quick start of the crop in a cold spring“, Michael Horsch tells about his experiences.
“In the past 10 years, we also dealt more and more intensely with direct seeding with discs.“ Especially in regions with a lot of water or in very dry conditions you need a sowing technology that moves considerably less soil than a tine coulter. In Brazil for example, the customers want to sow below the straw of the previous crops or the catch crop. If too much „open soil“ is left behind, the erosion risk increases considerably and soil temperature rises significantly because of the lack of soil cover. From an agronomic point of view, the HORSCH SingleDisc seed coulter has been optimised for as little soil movement as possible and a precise placement of the seed. “The seed coulter of our Avatar opens an extremely small furrow and places the seed very precisely at the bottom of the furrow. The adjustable closing wheel provides the required soil cover.“
Straw – support and challenge at the same time
“The harvest residues of the previous crop or of a well developed catch crop are a chance and a challenge at the same time.” Straw provides nutrients and organic matter and thus is an important building block of humus maintenance and humus production. The residues on the surface are an erosion protection and can cool the soil. “If we manage to achieve an intensive covering with straw mulch between the rows of the new crop, it might help in dry, hot conditions to prevent the soil from heating up even more.” The straw layer is a kind of insultation on the soil surface. The air buffers in the straw mulch keep the heat from the soil surface. Especially light straw, e.g. wheat straw, additionally reflects solar radiation. The result is that the soil heats up less. In regions with high temperatures and dark soils the effect can be particularly interesting.
Sowing in wheat straw with disc technology
However, not all straw is the same. You have to differentiate between the different crops that generate different amounts of straw and, of course, the characteristics of the residues. “It always is an enormous challenge if you want to sow in white, i.e. fresh wheat, barley or rye straw. Immediately after the harvest, the straw is very tough and not easy to cut. Sowing with disc technology involves the risk of the straw being pressed into the seed slot. As a result, seed-soil contact and emergence may suffer. “In this case, trash discs are a great help, but only if the row spacing is 25 cm.”
In direct seeding, brittle straw is much easier to handle. “If after the harvest there are four to five weeks of sunshine and perhaps a rain shower every now and then, wheat straw for example can be cut considerably easier with a disc and the risk of the so-called “hairpinning” effect is reduced significantly.”
If it is necessary to sow into fresh straw immediately after the harvest, is makes sense to cultivate the residues a little bit beforehand. A solution could be to drive over the field to align the straw and to bend it in advance. The resulting effect is the later the disc gets through more easily and draws less straw into the seed furrow. The Cultro is also very interesting regarding capillarity and water loss. “Even in very dry, dusty conditions you can still move the soil, even if it is only 1 to 2 cm. This is enough to close the capillaries. This is extremely important. For if dry cracks are closed, residual moisture moves below the layer of dust on the surface. If you, thus, draw up moisture from the soil and then sow, there is the chance that the seed will germinate successfully.”
To take up the topic of cracks again: If there are cracks in the soil, they will get larger and larger in case of an increasing and continuing drought. The cracks act like a chimney, i.e. water escapes through these cracks and evaporates. This, of course, complicates sowing and germination considerably. “A clayey soil will dry like concrete the longer the sun shines on it.” In this case, you have to close the cracks beforehand. Experiences from the past two years show that, in this respect, too, the Cultro is an excellent tool that requires only little effort.
Sowing into fresh wheat straw with tine technology
The alternative is to always work with tines if there is white straw. You can see this in France very often. “Over there, farmers equip their Sprinters with narrow tines to sow mainly catch crops, sometimes also rape. For with these narrow tines, straw can easily be removed from the slot.”
With catch crops, you do not have to attach major importance to the soil structure. “In this case, it is not about absolute perfection.“ However, if you want to get a main crop, e.g. rape, into the soil, the soil structure is very important even if the straw is under control. “If for example a lot of wheel tracks have been created in the field during the harvest, direct seeding may work, but you must not be surprised if the plants germinate worse and if the roots do not develop well in the area of the wheel tracks. Especially when combining you clearly see where the wheel tracks were. For in this area, the population is thinner and there may be yield losses. “
But you can develop a feeling for a good and correct soil structure. If the clods are porous and the pores are small, even a desiccated soil can take up water and swell. However, if the clods have smooth, sharp edges without pores you know that the soil is compacted. “In this case, it will not become better if it rains. On the contrary. It will even get worse. This is why in regions with direct seeding catch crops more or less play a major role to maintain the structures.”
As mentioned in the previous article, for cereals stubble length and straw distribution are important. There can quickly be a problem with mice what Michael Horsch considers to be the biggest problem in direct seeding in Central Europe.
Rotative direct seeding and why it more and more becomes an alternative in Central and Western Europe
Rotative direct seeding is more and more becoming an alternative. The driving factor of rotative direct seeding is, if conditions and soil structure fit, the condition of the residues and the previous crop. Direct seeding can be as good and as productive as sowing after intensive tillage.
“Rotative direct seeding is the alternating, but situation-adapted use of direct seeding from year to year and depending on the crop.” The drivers for this method especially in Europe are three essential factors:
- Not every crop rotation is suitable for direct seeding. In the rotations rape-wheat-barley or rape-wheat-wheat that were rather established in the past, it often was not possible to sow the following crop direct and achieve high yields. “We all have been very, very successful with these short rotations for many years. However, today, influenced by several factors like resistances, framework conditions etc, we are now back to broader rotations in many places.” If rotation includes 30 to 40% of spring crops like maize, soya, sugar beet or sunflowers, cultivation windows for catch crops open up. Or there are crops in the rotation that can be sown direct. “We often observe that our customers with a good catch crop in spring for example sow sugar beet in a perfect soil structure without any preparatory cultivation. So there is no point in creating tracks in the field with a seedbed preparation.”
- Another reason for direct seeding are the constantly increasing climate changes. “We notice that there are longer and longer, very hot and dry periods and that we have to sow certain crops in August/September, e.g. rape, catch crops or partly also early-sown wheat or barley. Each cultivation leads to more drying of the soil, less seed-soil contact, more clods and less fine earth etc. In such situations, it is better to leave the straw on the surface, close cracks and pores by a pass with for example the Cultro TC and then sow timely and with a little bit of moisture in the soil. In other words, sow in conditions where structure and straw are ok, where you can place the seed properly and where a cultivation is not mandatory. In principle: If there are many residues, you have to be more careful with direct seeding than if there are only a few residues like after soya, rape, sunflowers or peas.”
- In conditions with a very good soil structure, a broad rotation and a clean harvest resp. with enough time to allow the straw to mellow, rotative direct seeding is also interesting from a financial point of view. Less passes and thus less time, less machines and less diesel combined with an excellent sowing quality can also be an essential factor from an economic point of view.
“The topic of harvest residues, i.e. straw, runs like a common thread through direct seeding“, Michael Horsch sums up. Especially high amounts of cereal straw, mainly wheat followed by barley and rye. Rye is least problematic even with high quantities of straw, followed by barley, and wheat is most difficult. This is not so much due to the quantity as to the C/N ratio in the straw and thus, to the way it decomposes.