There’s been a big increase in the number of growers that are putting in cover crops around here this year. It’s a practice that’s catching on fast and for good reason – diverse cover cropping 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 seasonal weeds, growing high quality forage and attracting beneficial insects are outcomes that can all be achieved with a well-executed cover crop. That said, it is a relatively new practice for some and an awareness of all the considerations that determine the success of a cover crop is paramount.
These include the following:
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 of each you use in a mix. Broadly speaking:
- A diverse mix of annual cereals, legumes and other herbaceous species are recommended for seasonal soil improvement.
- Tall or vigorous annual cereals and broadleaf forbs make for better weed control
- Grasses and clovers as well as perennial herbaceous species that can handle grazing are good inclusions for forage situations
- There are numerous seasonal flowering species you can add to a mix if you want to attract beneficial insects
Composition of a cover crop mix
It’s worth checking the quantities of different species in cover crop mixes, firstly to ensure there are enough of the species you want but also to make sure there is 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 good and services 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 take well. In most cases, getting the seeds into the soil as opposed to broadcasting them on the surface is much 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 included, while there is still moisture in the soil and preferably with a decent spring rainfall event. With all the rain that’s fallen by this time of year there is usually an existing stand of plants that must be terminated somehow or at the very least, hard slashed or grazed prior to planting.
Even if you do manage to 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 support a cover crop 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 and rhizobium inoculants 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.
- Minute amounts of the required nutrients applied in furrow or the planting hole along with your seeds and seedlings are readily accessible at the beginning of a crops life.
- 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 or termination. 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). To get the most out of a seasonal cover crops let them grow until just before species start setting seed. This is a very expensive process and the point where plants drastically cut back on root exudation, direct significant amounts of reserves to fruiting and become much less palatable and nutritious to stock. Grazing or slashing may kill softer or taller annual species but grasses, clovers and perennial forbs regrow as long as conditions enable.
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. The percentage of each species in the mix is determined by the percentage of its full seeding rate you use. It is recommended that the combined percentage of all species included the mix totals no less than 100%