Planning cover crops and catch crops already at the sowing stage
Intercropping systems (cover crops) are increasingly treated as a standard element of agrotechnics integrated into crop rotation—especially in no-till systems, where maintaining continuous soil cover is crucial. Many farmers consider this already at the stage of choosing the main crop, and at the moment of sowing or harvesting they have the next step planned—either sowing a stubble cover crop immediately after harvest or undersowing a cover crop into a protective crop.
Stubble cover crop
A stubble cover crop is an intercrop sown in summer directly onto stubble after harvesting the main crop (e.g. winter cereals or rapeseed). Its sowing must be planned in advance so that seeds are sown as soon as possible after harvest, giving plants maximum time to grow before autumn.
Some farmers combine harvesting with cover crop sowing (installing a cover crop spreader on the combine) or sow 1–2 days after harvest. Alternatively, the last tillage pass can be planned to include sowing the cover crop, for example during shallow stubble cultivation. This allows cover crops to emerge quickly, using residual soil moisture and the long summer day.
Practitioners’ tip: if you do not have a dedicated cover crop seeder, use a standard fertilizer spreader to broadcast seeds on stubble and then pass with a disc harrow or harrow to shallowly mix seeds into the soil. This simple method is widely used on many farms.
Intercropping undersowing
The second option is intercropping undersowing, i.e. sowing cover crop species into a growing main crop, which acts as a protective crop—shielding young intercrops and limiting their excessive growth before harvest. Undersowing is most often practiced in spring cereals (especially spring barley), less often in winter crops (sometimes in rye or winter triticale). Planning takes place already at sowing or emergence of the main crop.
Example: when sowing spring barley, a cover crop (e.g. clover, serradella, or ryegrass) can be sown simultaneously or shortly after cereal emergence. Initially it grows slowly under the cereal canopy without excessive competition, and after cereal harvest it continues to develop independently.
When planning undersowing, select species that tolerate shading and water competition and have a slow initial growth. Full access to light and space comes only after harvest (August/September). It is also important to ensure that main crop treatments (e.g. herbicides) do not destroy the undersown crop.
Important! Planning intercrops at the sowing stage is part of crop rotation design. They should be treated on equal footing with any other agrotechnical operation—field selection, timing, and species choice must consider what is grown before and after cover crops.
Why is it worth sowing cover crops?
Some benefits of crop rotation—including cover crops—are described in e-book 1 (increasing soil organic matter and biodiversity, lower disease, pest and weed pressure, reduced plant protection costs). Here it is worth highlighting three more: improving soil structure, retaining nitrogen and other nutrients, and soil protection (against erosion and degradation).
Improving soil structure
Cover crops penetrate soil with their root systems, loosening compacted layers and binding loose particles into stable aggregates. Examples:
- Oilseed radish is known for its strong taproot that drills channels in the soil (acting like a natural “subsoiler”), facilitating root growth of subsequent crops and improving aeration.
- Buckwheat - releases substances from its roots that dissolve poorly available phosphates and calcium, increasing nutrient availability for the next crop.
Nitrogen retention and other nutrients
After harvesting the main crop, significant amounts of nitrogen often remain in the soil (from fertilizers or organic matter mineralization). Without plant cover, this nitrogen may volatilize or leach into groundwater.
- Fast-growing plants (especially white mustard, radish, phacelia) take up nitrogen and other nutrients (potassium, phosphorus, sulfur), binding them in biomass. These nutrients are not lost but “stored” until cover crop termination or decomposition, when they are released and become available for the next crop.
- Legumes (small-seed legumes such as clovers, serradella, vetch, as well as faba bean and lupine) additionally introduce “new” nitrogen into the soil, allowing reduced mineral fertilization of the following crop.
Soil protection
Maintaining continuous plant cover is a fundamental soil protection practice. Cover crop foliage shields the surface from raindrop impact (preventing crusting) and from drying effects of wind and sun, reduces evaporation and temperature fluctuations. Cover crops also enhance biological activity and suppress weeds and soil-borne pathogens.
- Rye releases compounds that inhibit germination of some troublesome weeds (e.g. pigweed, lamb’s quarters).
- Sunflower cover crops leave phenolic compounds in leaves that suppress weed growth after being washed into the soil by rain.
Important! In addition, cover crops can bring economic benefits. Some are grown for forage. For farms reducing livestock numbers, intercrops have even become a substitute for manure—supplying organic matter and nutrients while meeting agri-environmental program requirements (such as the “Intercrops” eco-scheme rewarding greening).
How to select species for reduced tillage systems?
In short,reduced or no till farming impose certain requirements on cover crops—they should prepare soil while not hindering sowing into mulch. Therefore, choose fast-growing species that provide specific soil benefits and are easy to manage (termination or winter kill).
More: e-book 3, chapter 4
Practice: cover crop sowing techniques in different situations
At the end, a few practical tips on cover crop sowing techniques.
Sowing a cover crop during the last tillage operation
It is worth combining operations in order to sow the cover crop efficiently and on time. If, after harvest, you plan stubble cultivation (e.g. with a cultivator or disc harrow), it is a good idea to sow the seeds during the same pass. This can be done using a cover crop seeder mounted on the tillage implement. If such equipment is not available, an alternative—as already described—is to use a fertilizer spreader to broadcast the seeds, followed by shallow cultivation (harrow or cultivator) to cover them. It is important to finish the soil after sowing, for example by harrowing or rolling, so that the seeds have good contact with the soil and moisture.
Example: farmers experienced in conservation agriculture often sow cover crops directly into stubble, sometimes even during harvest (e.g. a seeder mounted on the combine header that spreads seeds in front of the straw chopper).
Seeding of cover crops with a precision drill
Standard intercrops are usually sown with a row (grain) drill or by broadcasting, but there are situations where precision planters are used. Such machines (e.g. for maize or sugar beet) place seeds individually at fixed spacings. This can be useful when you want to sow larger seeds at wider row spacing or between the rows of an existing crop.
Example: in practice, farmers without a precision planter cope differently—they sow cover crops in a traditional way, but adjust row density instead (e.g. blocking every second opener in a grain drill to sow at 30 cm spacing, which is also a form of spacing control)..
Intercropping undersowing
The undersowing technique involves sowing seeds into an already growing crop (cereals). This can be done with a row drill, a spreader, or even manually, depending on the scale. Undersowing is often carried out at the cereal tillering stage or just before it (e.g. in spring barley 2–3 weeks after sowing).
It's crucial that the cereal crop isn't sown too sparsely (otherwise, the undersown cover crop could overdevelop excessively). Moreover, for a period after cereal harvest, herbicides that might harm the undersown crop cannot be used. Weed management in undersown crops primarily relies on competition—a dense undersown crop restricts weed growth (by thickening the crop canopy).
