Potatoes are field crops that require deep soil, rich in organic matter. Planting can start as early as February for new potatoes, and continue until May for a harvest from June to October. Before planting potatoes, cover crops can be sown, but not just any. Multi-species mixtures are very good for quality and yield, as well as providing agronomic benefits in terms of soil structure and releasing fertilizing agents.
The benefits of cover crops in crop rotations
There are two main reasons for planting an intercrop before tubers. The first is to fix nitrates in the soil, which will be used again when the following crop has been sown. The second is to improve potato quality and yield.
Choosing an inexpensive cover crop
Many potato fields are planted with mustard or brown mustard first. Crucifers are very easy to sow, as the seeds are small and don’t need to be covered with soil. Broadcasting is often the method used. The seeds are inexpensive and fast to sow compared to having to use a classic seed drill. The crop is also easily destroyed by frost. Brown mustard has an even greater biomass production capacity than traditional mustard, as well as a better biofumigation effect on fungi and nematodes. Daikon radishes are a good option too: the tuber is deep (15-20cm), if sown early. They are rich in water and non-woody, if the variety is well chosen. The non-woody aspect makes them less prone to disease.
Choosing cover crops: phacelia?
Phacelia is from the hydrophyllaceae family. It has large seeds that needs to be sown with care using a conventional seed drill. Seeds must be well covered with soil. Seeds are expensive, but the plant has many advantages. It is very easy to destroy, especially by frost. Shredding is not necessarily required as the stem is quite brittle. A phacelia – oat mix works well before potatoes. Care is required with phacelia, however, to avoid sclerotinia.
Sowing dates and multi-species cover crops before the following crop
In several trials, multi-species cover crops proved to be more advantageous than a single-species cover crop. They are more resilient to variations in soil and climate conditions. The development of different families of species depends on the amount of nitrogen in the soil. Grasses and crucifers do better when there is sufficient nitrogen in the soil, which is not necessary for legumes. Multi-species cover crops are often effective biomass producers.
In addition, nitrogen is released into the soil progressively with mixtures because different species have different nitrogen-releasing speeds. Classic nitrogen-fixing intermediate crops, such as radish and oats, can be incorporated too, as well as phacelia and legumes. Seeding is more complicated though, as the seeds are different sizes and have different needs. Whatever the choice, the earlier the seeds are sown, the more biomass will be produced.