Cereal seeding: singulation or even depth placement - what is more important?
“Normal” seeding conditions with moderate rainfall for an even emergence are becoming scarce. Instead, longer dry or extremely wet periods will increasingly characterise the seeding periods.
While in dry conditions the grain should be placed in a well reconsolidated seed furrow with a reliable supply of water at germination to achieve safe emergence, in wet conditions the objective is to seed and to not be embed the seed too firmly. Weather extremes also influence the intensity of tillage and thus also the seed coulter. Tillage can be roughly divided into four intensity levels: inversion tillage, mulch seeding, minimum tillage and direct seeding. The intensity of tillage is often influenced by external conditions.
Embedding and singulation
For drill seeding, many farms rely on disc seeding technology. What systems are available on the market and how do they differ with regard to the shape of the seed slot? The most universal and most widely used method in practice is sowing with the double disc coulter. By pressing the seed furrow open, it compacts the soil at the left and right side of the furrow wall (see ill. 1). The placement depth is maintained by the leading packer and the following press wheel. A uniformer or possibly a catching roller presses the seed to the bottom of the furrow. The following press wheel closes the furrow. In practice, this coulter is used to sow after tillage with a row width of around 15 cm. Seed singulation is recommended for crops that do not branch or tiller, e.g. sugar beet and maize. Based on our many years of experience with the singulation of cereals, we can summarise as follows: Singulation only has a positive effect starting from seed rates below 150 grains per m². Much more decisive than singulation is the precise placement of the seed in a perfectly consolidated area and at the same depth. A double disc guided on the left and right side opens the seed slot. Consolidation is achieved by the depth control rollers along the seed discs to below the seed furrow (see ill. 3). The seed is then pressed into the consolidated area by a catching roller.
Closing wheels close the seed slot and cover the seed. As a result, the radicle finds compacted soil at the bottom and the sprout finds loose soil at the top. The two depth control wheels next to the discs require space and therefore, row widths of less than 22.5 cm are not possible even with a coulter stagger. This method achieves the most reliable emergence in drying or dry conditions. Accordingly, this seeding system is used more and more frequently for rape seeding. In wet conditions, the design-related, heavier coulters easily push too much air out of the soil. The side walls also are often too hard in wet conditions and the roots of the germinating plant develop poorly.
The single disc seeding technology is widely used for direct seeding. The corresponding coulter usually is heavier and therefore can apply a higher coulter pressure which is required for direct seeding. However, seeding can also be carried out after tillage on well-settled soils - using the stale seedbed method, e.g. for the problematic weed black grass. With this method, the depth is set directly next to the seed disc, similar to the single grain seeding technology. The disc and the skid open the seed furrow (ill. 2). Here too, the seed is pressed into the furrow bottom with a catching roller or a firmer. The closing wheel then covers the seed with soil. The depth control directly on the disc allows for sowing without a packer. Row widths well below 20 cm can only be realised with a coulter stagger (short and long coulter).
Row width
When drilling cereals, row spacing is a permanent topic of discussion. There are arguments for and against narrow and wide row spacings. Closing the population to quickly develop strong competitive power speaks in favour of narrower row widths. Reliability and precise embedding speak in favour of wider row widths. Over the years, approx. 15 cm have proved to be a good compromise. However, this row width requires a coulter stagger to avoid blockages. Coulter stagger means that short and longer coulters are installed. As a result, the front coulter throws soil in front of the rear coulter and the rear coulter throws soil onto the seed row of the front coulter. Due to the system, the conditions for embedding and depth placement are different for the front and rear coulters. The more free-flowing the soil, the more noticeable the difference. This can only be remedied with a 1-bar seeding system. In this case, the conditions are the same for all seed rows. More row width is required for a reliable machine. Additional rows, thus, contribute to a more precise depth placement.
Points for discussion
Precise placement depth:
- Equal starting conditions for every plant - internal competitive pressure from plants that emerged later
- Compliance with the depth placement and secure covering of the seed - avoidance of herbicide stress for the crop or roots
- Even cereal populations are easier to manage - scheduling of herbicide, fungicide and growth regulator etc.
- For mechanical weed control, even depth placement is a basic prerequisite for an optimum tool adjustment.
Singulation:
- Positive experience with seed rates below 150 seeds/m²
- A must for crops that do not tiller or branch
Taking all the current challenges of drill seeding into account, e.g. reliable emergence in dry conditions, wetness or prevention of herbicide stress, embedding and deep placement (especially with seed rates well over 150 seeds/m²) are more important for an even population than singulation.