One species of nitrate-fixing intermediate crop can be sown or a mix. Mixing species has many benefits. Definition, advantages, and examples of effective mixes from an agronomic perspective.
Reap the benefits from each species by using the right mix of nitrate-fixing intermediate crops
A mix of different cover-crop species can be beneficial because the virtues of each species are combined. They all have different characteristics in terms of germination, development, sensitivity to light, and absorption of water and nutrients. Combining them increases the likelihood that the cover crop will cover the field completely. It also guarantees good cover-crop development in uncertain weather conditions, as has been the case in recent years. More biomass is produced due to the competition between species. Competition between species also reduces weeds and the risk of single-species pests damaging an intermediate monoculture.
A mixture also improves the soil structure as the different root systems grow to different depths, occupying the soil more completely. It can also reduce costs when cheaper seeds are mixed into higher-priced ones.
Put a legume in the mix of intermediate crops
From an agronomic point of view, a single legume can be planted as a nitrate-fixing intermediate crop. However, it is recommended to limit it to 75% of the total cover crop. It is less efficient at trapping nitrates than other crops, but it releases nitrogen for the next crop in the rotation. It is often sown as part of a nitrate-fixing intermediate crop mixture. Physiologically, it uptakes nitrogen from the soil at the start of its cycle, but then absorbs atmospheric nitrogen, leaving the nitrogen in the soil for other species. Legumes are also high biomass-producing crops.
What are the agronomic criteria for using a mix of nitrate-fixing intermediate crops
To develop an effective mix, it is worth thinking about your aims before choosing your species. If your aim is:
- to restructure the soil, you need to combine species with complementary root systems.
- to reduce nitrate leaching and to obtain green manure, mixing grasses with legumes will work well.
It is also possible to replace grasses with crucifers which cover the soil more completely.
In all cases, a mix that reduces parasites should be chosen. Make sure you take the size and density of the seeds into account too, to facilitate seeding. Legumes often have bigger seeds and need to be sown deeper. A field bean/mustard mix can be sown in two stages: with a seed drill for the field beans and a spreader for the small mustard seeds.
Example mixes:
- spring vetch and oats
- winter turnip and rye
- red clover and Italian ryegrass
- mustard and clover
- vetch, clover, and phacelia
- vetch, oats, and phacelia
- triticale and turnip
- oats and daikon
- clover, mustard, and phacelia