Cover crops - purpose, sowing dates, number of species in the mix, which cover crop for which cultivation, species for stubble and winter cover crops, threats from stubble cover crops
The idea of cover cropping
Catch crops are now a formal requirement of EU legislation. Their primary disadvantages include relatively large water requirements, particularly in drier conditions, and the need for skillful incorporation into existing crop rotations. However, proficient management of catch crops offers significant benefits to the soil, which remains our primary interest.

From an agricultural perspective, the purposes of sowing catch crops include:
- providing the soil with organic mass to build humus
- stimulating the microbiological life of the soil
- absorbing and releasing nutrients for crop plants
- stabilizing the soil and protecting it from erosion
- shading the soil and reducing water evaporation
- improving soil structure

Catch crop sowing date:
In brief: the sooner, the better. This is particularly relevant for stubble catch crops, which have only a few weeks to grow in the field between the main crop plants. Sowing should take place immediately after harvest to utilize the moisture remaining in the topsoil for germination. It is essential to focus on species that will grow quickly.

Winter cover crop
For winter cover crops, the sowing date is later but must ensure that plants grow for approximately 60-90 days, depending on weather conditions. Early sowing promotes vigorous growth. If the plants flower, their lignification will begin, making mineralization in the soil more difficult. However, legumes in the catch crop mixture assimilate nitrogen best before and during flowering, and their tissues do not lignify to the same extent as, for example, cabbage species. If the catch crop has grown sufficiently and the weather is conducive to further growth, it should be eliminated, preferably with a disc harrow, to mix the plants well with the soil. The Rolmako SpeedCutter disc harrow is optimal for shallow incorporation of the catch crop into the soil, along with other models such as the U693 or U652. To enhance the cultivation effect, trailed machines with a knife roller working in front of the disc section are recommended. For mounted disc harrows, Rolmako offers the ProCut or TurboCut double knife roller mounted on the front three-point linkage. This combination of tools optimizes catch crop management and improves post-harvest soil processing. For a grown winter catch crop that must remain in the field until spring, vegetation can be interrupted with a knife roller, which cuts the plants without mixing them with the soil. If the catch crop survives the winter, it should be destroyed in early spring before the next crops. Ensure that the remains are properly incorporated into the soil to accelerate decomposition and nutrient provision. Light cultivation to a depth of 5 cm is often sufficient, although the depth may vary based on the machine and soil conditions.
Number of species in the mix
The standard is 2-3 species in the mixture. It is optimal if they originate from different groups, such as legumes, cabbages, asteraceae, or phacelia. You can select ready-made mixtures available on the market or create your own. If the mixture contains 2 species, each should be sown at half the norm for pure sowing. Similarly, for 3 species, each should be sown at 30% of the norm for pure sowing of the respective plant.

What species are in the cover crop?
The crop rotation plays a critical role. In rotations with rape, avoid sowing cabbage species, such as mustard or radish. Sunflower should also be avoided due to susceptibility to sclerotium rot. For rotations with rape, legumes (preferably small-seeded and not prone to sclerotium rot), phacelia, or buckwheat are advisable. When corn is part of the rotation, both cabbage and legume varieties can be successfully sown as catch crops. In potato rotations, avoid phacelia to prevent the multiplication of soil viruses that affect potatoes. In beet rotations, buckwheat is risky due to its uneven ripening and quick seed shedding, which leads to difficult-to-combat spring weed infestations. A high proportion of cereals in the crop rotation suggests avoiding them in catch crops. Many ready-made mixtures include oats, which, while phytosanitary regarding diseases at the stem base, attract aphids that may carry viruses to winter crops.

What to sow as a cover crop
Select an appropriate mix of species based on your objectives (enhancing soil structure, nitrogen fixation, weed control, etc.). Integrate catch crops into your crop rotation system to leverage species diversity. Utilize specialist seed drills for sowing catch crops, such as the APV offered by Rolmako, which can be mounted on any disc harrow (e.g., Rolmako U693, U652) or cultivator (e.g., Rolmako U436, U453). These seeders can also be mounted on the front three-point linkage of the tractor and should facilitate simultaneous sowing and cultivation. Sowing depth varies by species: for most catch crops like mustard or vetch, the recommended depth is 1 to 3 cm. Adjust sowing depth according to soil conditions and moisture. Prior to sowing, avoid heavy soil compaction and refrain from applying herbicides, as they can adversely affect catch crop germination. Ensure the soil is in optimal condition and neither too wet nor dry.

The catch crop extracts water
Excessive soil drying is the primary disadvantage of catch crops. A catch crop grown to 10 cm requires approximately 10-12 liters of water per square meter. Prolonged presence in the field may result in up to 100 liters per square meter of water consumption. "Extracting" this large amount of water from the soil can cause autumn difficulties in soil conditioning and site preparation for the next crop (e.g., excessive clumping of the seed layer, leading to uneven emergence of cereals or rapeseed).
Summary
Cover crops are essential in sustainable agriculture, protecting soil, enhancing fertility, improving structure, and controlling weeds. Proper cover crop management necessitates adapting practices to local soil conditions, climate, and farm goals. Consult your local agricultural advisor or soil specialist for additional information and recommendations.

Terminology
Sclerotinia rot - is a soil-borne disease, the main symptoms of which are primarily visible on the outside and inside of infected plants in the form of abundant white mycelium growth, where over time it leads to the development of sclerotia.