To compare the root development of rapeseed depending on tillage intensity, we take a look at our demo garden.
For since 1997, the tillage block laid out as a long-term test has been the centrepiece of the demo garden. In four successive fields, the influences of tillage can be examined and compared with regard to different parameters, e.g root development.
A field simulates a multi-part rotation consisting of wheat, maize, rapeseed and, depending on the grass and disease pressure, one legume (field bean or pea). Field 1 was ploughed. In field 2, the soil was loosened with a Tiger at a depth of approx. 20 cm. In field 3, a reduced tillage was carried out (mainly with Terrano or Cruiser) at a depth of 10 cm. And in field 4, there was no tillage at all.
The conditions at the time of seeding but also at the time of the preparatory cultivation were wet and unsettled. Capillarity was often destroyed by tillage or too short seed windows resulted in a “smearing” of the seed.
After the seeding season, there was a dry period in September which meant that a lot of populations in the region did not emerge until the beginning of October. So the farmer has the difficult choice between „badly sown“ or „not seed at all“.
In our demo garden, rapeseed was sown at the end of August in a relatively short time window between two rainy periods (35 grains/m² LG Ambassador). In field 1, after the plough, a power harrow seed drill was used for seeding with a row spacing of 15 cm. In field 2 and 3, seeding was carried out with the Pronto DC with an integrated tine zone and also a row spacing of 15 cm. In field 4, the direct seeding lot, the Avatar SD (16.7 cm row spacing) was used for seeding. In addition to the seeding methods used in these four fields, the StripTill method was tested with the Focus in a separate lot.
In total, the seeding conditions at Sitzenhof were very challenging and this is also reflected in the rating of the rapeseed roots.
A well branched plant with a strong main shoot does not imply a nutrient deficiency. The root collar diameter is acceptable. The abrupt break of the root collar diameter is at a depth of 4 to 5 cm, directly at the depth of the rotary harrow. Though some smaller roots managed to develop the horizon below, the smear layer that was created by the rotating power harrow tines still are clearly visible. In this case, the soil structure that was destroyed by the plough was no match for the power harrow.
In the second field, too, the wet cultivation of last year becomes visible. Due to the higher, buffering mulch share in the upper layer and the lesser active interference by the tine zone (compared to the power harrow), the mechanical “lock” respectively the disturbing layer is not as distinct as in field 1, but it is still visible. The tap can clearly develop more depth, but the growth of this root, too, is limited. It becomes clear that the risk of smear layers and compaction caused by disc harrows in wet conditions must not be neglected.
Due to the relatively shallow tillage at a depth of max. 10 cm, the root developed optimally in the loose area. The root collar, too, shows a clear swell. The following abrupt change to a highly branched, finer root system implies that there was compaction in this area which then was grown around and penetrated. However, a distinct tap root, as it is typical for rapeseed, does not exist. There are rather several second-order roots.
In the direct seeding field, the plant development in general is delayed by approx. two weeks compared to the fields that were cultivated at a depth of for example 20 cm. The reason is the slower soil heating in spring. This slower heating results from two factors. Factor one is the covering of the soil with organic matter that extremely limits the heating by the reflection of the sunrays. Factor 2 is the soil density per cm3. Because of the lacking loosening, the gas exchange and thus also the exchange of warm and cold air is affected. The soil temperature in the direct seeding field is lower than in the cultivated fields, but here the rapeseed formed a clear tap root. The explanation: compared to the cultivated fields, the soil is more compacted, but it does not show any abrupt changes.
In the overall comparison, the rapeseed that was sown with the Focus performed best. The tap root has developed well and the size of the root collar with 3 to 4 cm is optimum, too. The root mass is reasonably well distributed although some more roots in the depth would be desirable. However, the lacking root share in the depth results from the currently very cold and wet weather. It is important to observe the development progress when drought sets in.
Only the vertical compactions caused by the point restricted the lateral root growth and resulted in an increased growth along the loosening strip. This effect of furrow wall smearing is mainly known from maize but can also be caused by excessively wet seeding conditions.
In general, all populations appear to be vital. The currently abundant rainfall so far has supplied the plants without any deficiency. The predicted early summer drought will be an exciting time. During this stage when the TSW is determined and which, thus, has a great influence on yield, optimum root development is most important.
The conclusion of the assessment is that smear layers – vertical as well as horizontal ones – and also compaction in the soil have to prevented if possible. In a year with (too) much humidity in the soil, the advantage of direct seeding may be that no additional disturbing layers are created in the soil and thus, roots can develop evenly.
