Multi-species cover cropping is a practice that’s catching on fast and for good reason – it is one of the most important tools to emerge out of the regenerative movement happening around the world.
Vastly improved soil function and fertility, smothering of seasonal weeds, growth of high quality forage and attracting beneficial insects are outcomes that can all be achieved with a well-executed multi-species cover crop. That said, there are a number of important considerations that must be taken into account when planning a cover crop.
Reasons for growing a cover crop
Cover crops can be used in a wide range of situations. It is important to know beforehand what the reasons are for growing a cover crop as this dictates the species and rates you use in a mix.
There are annual species that are usually included as staples in most mixes. These can be used as a bulk base mix for a range of situations to which other species are added in order to tailor it to desired outcomes. The portions used vary with context and the emphasis on other species in the mix.
- Base mix cool season species generally include annual cereals (oats, cereal rye, triticale, barley etc…), legumes (field peas, vetch, white lupins etc…) and brassicas (tillage radish, kale etc…)
- Staple warm season species include cereals (millet, sorghum etc…), legumes (cowpeas) an other forbs such as sunflowers, phacelia etc…
- The inclusion of a good portion of seasonally appropriate annual cereals, legumes and other forb species from different families is recommended for rapid initial soil improvement and to generate biomass. Perennial species are great for deeper long term soil development.
- The use of established annual and perennial grasses, clovers and other herbaceous species like chicory that can handle repeated grazing are standard for forage situations. Avoid adding too many vigorous cereal and legume species when seeding a pasture mix as they can smother slower growing perennial species.
- In orchard and vine situations a range of both annual and perennial species may be suitable. In cropping or vegetable production situations perennial species and some annuals can become weeds so should only be included if there is a management strategy in place.
- Fast growing, short lived species can be used as a filler crop between seasons. These include species like Buckwheat, White Lupins, Field Peas, Turnips etc…
- Tall or vigorous annual cereals, legumes and broadleaf forbs can be used to smother seasonal weeds.
- There are numerous seasonal flowering species from a range of forb families such as that you can add to a mix if you want to attract beneficial insects i.e. BRASSICACEAE, ASTERACEAE, APIACEAE, LAMIACEAE, CHENOPODIACEAE, BORAGINACEAE etc…
- Many edible species go well and may be included in a multi-species mix. These include Cereals, Sunflowers, Rocket, Coriander, Silverbeet, Asian Greens, Turnips, Radishes, Kale, Lettuce, Pumpkins, Squash, Corn, Black Eyed Beans, Flaxseed, Chicory etc…
Composition of a cover crop mix
A good cover crop mix should have enough of the species you want, none that you don’t want, and reasonable representation from a range of family groups. The critical mass and proximity between types of plants and the microbe communities they support determines the supply of goods that can be shared via the underground network. This makes all the difference to the health, growth and resilience of a mixed cover crop and it’s effectiveness.
Sowing a cover crop
The right temperature range, adequate moisture and minimal competition from weeds in the early stages of growth are all essential if cover crops are to do well. In most cases, getting the seeds into the soil as opposed to broadcasting them on the surface is more successful. Exposed seeds are prone to drying out and being eaten by wildlife.
Sowing cool species as close to the break of season as possible helps them get a jump on weeds and make good growth before winter. However, if you sow too early, seed that germinates in an isolated rain event can die with lack of follow up rain. It’s best to look out for a good cool season type of front and not be tempted to sow with an early front that comes from something like cyclone activity further North etc… As a general rule of thumb it’s probably best not to sow before April. If you miss the break some sort of pre planting weed control must be carried out to ensure a good take in which case sowing can be carried out all till the end of autumn.
Unless you can irrigate, the window for sowing warm season cover crops in our Mediterranean climate is much tighter. They must be sown as soon as temperatures are warm enough for the species involved, while there is still moisture in the soil, and preferably with a decent spring rainfall event. Unless some form of weed control has been in place, there is usually an existing stand of cool season plants that become increasingly demanding over spring as they go to seed, depriving freshly sown cover crop species of the water and nutrients needed to get established. These must be terminated somehow prior to planting a warm season cover crop. Tillage at this time of year can be quite damaging and spraying is not an option for organic operators. Prior planting of an annual species, cool season cover crop that smothers weeds and and is slashed, rolled or grazed before seeding a warm season cover crop may be an option. Even if you do get a good take with your warm season cover crop, it may struggle to get through the dry season. Obviously, the better your soil function and carbon levels, the longer it can hold onto water and keep growing into summer.
Giving it a good start in life
Getting a cover crop off to a good start goes a long way towards ensuring its success.
- In biologically compromised soils, seed coating or in situ application of fungal rich compost/vermicast extract along with appropriate mycorrhizal/rhizobium inoculants and bio-stimuants is well worth doing from a cost/benefit perspective. These measures ensure good colonisation of beneficial microbes as soon as roots emerge and get the whole soil plant, microbe exchange system off to a strong start.
- Small amounts of certain minerals, applied with seeds in and seedlings at planting, gives plant roots and associated microbes instant access to what they require from the beginning.
- Post germination foliar sprays and drenches with products like fish hydrolysate, liquid seaweed, fulvic acid, compost tea, biofertilisers etc… are most effective when the plants are young. You need to use increasingly larger amounts, as the plants get bigger.
Getting the most out of a cover crop
Focusing on photosynthesis is a good way to think about managing cover crops in terms of building soil and how you time grazing. The energy harvested from sunlight by plants is what drives all living processes (in this way, the capacity summer cover crops have is greater, if you can grow them). The more vegetative growth you get out of a cover crop, the better. Once plants start to set seed however, they drastically cut back on root exudation, use up significant amounts of water and nutrients and become less palatable and nutritious to stock. Grazing or slashing before seed set can be used as a strategy to initiate vegetative regrowth from a range of species including grasses and clovers .
The grasses and forbs grown in diverse cover crops are very much the type of higher plants found in the fertile grasslands, meadows and prairies that came later than forests in the evolutionary picture. These next level communities sequestered large quantities of atmospheric carbon in stable carbon based soil humus structures at a rapid rate. Putting it simply, cover crops are not only a great strategy we can implement to benefit our operation but also one of the best measures at our disposal to help mitigate climate change.
To see what kind of cool and warm season cover crop species you can grow in this region, and the rates to sow them at, refer to our Cover Crop Seeding Rates Chart – CCSeedingRates. The percentage of each species in the final mix is determined by what percentage of its full seeding rate you use. It is recommended that the combined percentage of all species included the mix totals over 120 percent.Download Cover Crop Seeding Rates