Rapeseed roots: what you reap is what you sow
Crop rotation plans for the coming year should be first priority by harvest time at the very latest. If a decision in favour of winter rapeseed is made, preparation for sowing begins along with the grain harvest. And with preparation for sowing comes the manifestation of rapeseed roots, which determines a large portion of the rapeseed harvest.
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Compared to other preceding crops, winter barley is definitely the best preceding crop for rapeseed. It allows enough time for the harvest residues to be properly incorporated, thereby guaranteeing a good field emergence for rapeseed. The leftover quantities of straw determine the field emergence for late sown grains. If the straw remains on the ground, the use of a plough can lead to a clear improvement in field emergence. However, this carries the risk of straw mats building up and an impaired rapeseed root. If the straw ploughed in at the end of August has not decomposed by the middle of April, it forms a barrier for the rapeseed roots and the capillary ascent.
This leaves the question of whether mulch seeding is a better choice. The remaining surface straw does not disturb the underground. However, with mulch seeding, the straw is directly at the seed level and this can present its own challenges. During sowing, the remaining straw makes guiding the coulter – and subsequently, exact placing – difficult. The grains are placed directly in the remaining straw. This essentially leads to lower field emergences in the mulch seedbed. In practice, mulch seedbed stocks are frequently up to 20% thinner, compared to areas where the straw has been cleared. For example, straw layers also offer areas for uninvited guests such as slugs and field mice to retreat to.
If the stock is established, there is room for the root to move in the mulch seedbed – however, only if there are no other obstacles to overcome. If the underground soil is compacted, the rapeseed root faces a difficult challenge. In some cases, the rapeseed root adjusts the development of the root directly above the compacted area. The resulting slab-like structure reflects the compacted soil. This is frequently caused by a high level of moisture in the soil during harvest. The heavy loads of the harvesting machines press the moist soil into slab-like structures. If compacted areas are not dealt with, this can result in a stunted and buckled tap root which barely penetrates through the topsoil. If compacted areas are present, rapeseed, in particular, is a crop which can loosen soil and increase yields. Targeted loosening of soil results in higher yields, not only for this particular crop but also for future crops.
In order to sow rapeseed as perfectly as possible, the following points should be considered:
Threshing the preceding crop:
Does the straw remain on the surface?
- Then chop it short and distribute it well.
- Use a chaff spreader to avoid chaff dumps.
- Start tilling the soil directly after harvesting. Save water, especially in dry areas (excellent consolidation).
- Break up compacted soil under dry conditions.
- Create at least 20 cm of root space, deal with any combine harvester tracks.
- Work nutrients in deeply to create an attracting effect.
- Consolidate well, but do not fill in.
- Create sufficient contact with the soil for the rapeseed seeds.
- Leave as little straw as possible in the seeding row.
- Soil conditions take priority over seeding dates; it is better to sow in drills under good conditions, rather than on the desired date.
If the above parameters are taken into consideration, the root will develop well and nothing should stand in the way of the decisive factor for an ideal rapeseed yield. Measures such as crop protection and fertilisation accompany cultivation throughout the year, but can never compensate for deficits in the soil structure. If the right variety is chosen, a yield of 5–6 tonnes of rapeseed per hectare is possible, depending on location.
For further information, contact Eckhard Seemann, telephone number +49 (0)175- 2958438, firstname.lastname@example.org.