Pelletizing seeds to facilitate spreading
The broadcast seeding is practiced by several farmers (see Broadcast Seeding Sheet). However, the technique often faces the difficulty of spreading seeds at the same width as fertilizer and thus reusing existing passes and equipment (centrifugal spreader). Moreover, this choice of planting technique limits the range of available species to a few species whose seeds are large enough (and heavy) to behave like fertilizers.
An identified solution during the investigation would be to agglomerate small seeds onto carrier seeds that can be spread over large widths. Thus, farmers from Charente, and from the GIEE Magellan in Nièvre, have developed a method based on the use of a binder and a drying agent.
These farmer groups mainly use spring protein pea seeds as carriers onto which cover crop seeds are glued. However, this species is not very effective at germinating on the soil surface and most of the seeds do not germinate at all. Thus, within the framework of the “Multifunctionality of cover crops between crops” project, other carriers have been proposed and tested in the field under real spreading conditions.
Composition
To add weight and be able to spread all types of seeds over a wide area, it is necessary to glue them together. The produced aggregates must be strong enough not to be completely destroyed during spreading.
To perform the operation, a binder (such as molasses) and a drying agent (such as bentonite clay, pastoral clay, or flour) must be used. The proportion of clay and molasses represents about one quarter to one third of the total mixture (seeds + molasses + clay). It is enough to divide the seed quantity by 2 to know the amount of binder needed.
The proportion of glue (molasses) and drying agent (clay) can vary depending on the type of molasses used, but generally the various tests show good results for 1/3 molasses and 2/3 clay. The following rules are then obtained:
- Total quantity to spread (kg/ha) = seed sowing rate (kg/ha) x 1.5
- Quantity of clay (kg/ha) = seed sowing rate (kg/ha) x 0.33
- Quantity of molasses (kg/ha) = seed sowing rate (kg/ha) x 0.16
Some mixtures made during the two years of seeding trials in the previous
Pellet 1 - Common vetch + Phacelia + Abyssinian mustard + Alexandrian clover + Foxtail millet
| Species | Rate (kg/ha) | Proportion (%) |
|---|---|---|
| Phacelia | 1.5 | 3 |
| Common vetch | 30.0 | 60 |
| Abyssinian mustard | 1.9 | 4 |
| Alexandrian clover | 1.1 | 2 |
| Foxtail millet | 4.0 | 8 |
| Clay | 6.8 | 14 |
| Molasses | 4.4 | 9 |
This is the first tested recipe. The common vetch then serves as a carrier for the other seeds in the mixture. The quantities of common vetch proved to be somewhat high, considering the fairly high germination rate of the species.
Pellet 2 - Common vetch + Phacelia + Forage radish
| Species | Rate (kg/ha) | Proportion (%) |
|---|---|---|
| Phacelia | 3.0 | 7 |
| Common vetch | 20.0 | 49 |
| Radish | 5.0 | 12 |
| Clay | 8.4 | 21 |
| Molasses | 4.2 | 10 |
In this mixture, vetch still serves as a carrier, but in a smaller proportion. It is combined with forage radish and phacelia which showed good results in broadcast seeding.
Pellet 3 - Spring barley + Phacelia + Abyssinian mustard + Alexandrian clover
| Species | Rate (kg/ha) | Proportion (%) | Pellet 2 |
|---|---|---|---|
| Phacelia | 3.0 | 4 | 3.0 |
| Abyssinian mustard | 3.0 | 4 | 3.0 |
| Alexandrian clover | 3.0 | 4 | 3.0 |
| Spring barley | 40.0 | 56 | 40.0 |
| Clay | 14.7 | 21 | 14.7 |
| Molasses | 7.3 | 10 | 7.3 |
This mixture was composed with the aim of finding an alternative or complement, spring barley, less expensive than common vetch.
Pellet 4 - Small seeds
| Species | Rate (kg/ha) | Proportion (%) | Pellet 2 |
|---|---|---|---|
| Phacelia | 3.0 | 4 | 3.0 |
| Abyssinian mustard | 3.0 | 4 | 3.0 |
| Alexandrian clover | 3.0 | 4 | 3.0 |
| Spring barley | 40.0 | 56 | 40.0 |
| Clay | 14.7 | 21 | 14.7 |
| Molasses | 7.3 | 10 | 7.3 |
This mixture only combines small seeds, glued together to form larger aggregates with the idea of doing without carrier seeds such as vetch, pea or spring barley.
Preparation
Tip: The concrete mixer should not turn too fast to avoid breaking freshly formed pellets. To ensure good flow of the pellets, it is important that they are sufficiently dry and stored in a properly ventilated environment.
Properties
Seeding
Seeding is done using a centrifugal spreader. Since the pellets have a large diameter, it is preferable to perform a flow test to adjust the tool.
Further information
2019 Trial Results
Cover crop emergence
Produced biomass
Effect of coating on emergence and cover crop development
According to Bekuzarova et al. 2015 and Suliasiha and Widawati 2017, coating seeds with molasses and clay promotes emergence and development of young plants.
However, the trial network did not reveal differences in emergence rates between coated and uncoated seeds.
Source
Available at: https://cultivons-les-couverts.agro-transfert-rt.org/pellet/index.html
