Recent years have seen increased interest in the introduction of cover crops and how they can help improve soil health, structure and, ultimately, crop yields and profitability. This short technical document is a summary of what needs to be considered, should you be thinking about introducing the practice on your farm.
Please view it as a ‘How to’ guide, helping you to make the most of the potential benefits that cover crops can provide in an arable farming environment.
The Benefits of Cover Crops:
• Helps to boost organic matter content increasing water holding capacity.
• Help to improve soil health and structure, making it easier to cultivate.
• Improves soil biota numbers and activity (particularly worms).
• Cover to prevent soil erosion and keep the soil working.
• Used to capture nutrients left in the soil, and prevent leaching.
• Provide weed suppression – useful tool in black grass control.
• Oily radish can be used to control nematodes.
There are some considerations that need to be evaluated: The cost of seed and crop establishment. The time required at a busy period to establish the crop and the cost of spraying off the cover crop and incorporating the biomass into the soil. However, those farmers that grow cover crops whenever they can have seen improvement in soil health and measurable improvements in crop yield.
When to Establish a Cover Crop
Ideally whenever ground is going to be bare for a while. There are 2 key growing strategies:
1. Post-harvest catch crop- drilled directly after harvest before the end of August and destroyed in October for winter crop establishment – key tool for blackgrass control
2. Over wintered cover crop again established straight after harvest to over winter, destroyed late January to early March to drill a spring crop
The key to success is getting the cover crop well established, as early as possible after harvest.
At a busy time of year this can be challenging but worth spending the time it takes to get a rudimentary seed bed and adding a small amount of fertiliser to get the crop growing.
Clearly the weather and rainfall, makes a huge difference to establishment but giving the cover crop the best chance at the early stages, is key.
Selecting the Correct Cover Crop Mix
Getting the right cover crop varieties or mix is important. There are now many seed mixes out there with lots of exotic plants sold at great cost, however as with many things in life keeping it simple is often the best way. Some farmers have had great success just planting oats straight out of the grain store.
Different cover crops can offer different benefits. The list is endless, so we will look at a few key ones which have been proven to offer the best results.
Black oats an aggressive growing plant which has been shown to have an allelopathic effect, helping to reduce weeds especially blackgrass, which is making farming on some soils almost impossible.
Hungarian Grazing rye will grow in wet soils and therefore also cold soils and will produce green matter and a fibrous root structure at exceptionally low temperatures and is relatively cheap.
Radish and Mustardshave many derivatives, the high glucosinolate fodder radish or brown mustard can reduce nematode populations. These can be used as part of a gasification process to kill the highly resistant eggs of PCN (see technical paper by Bill Watts of Harper Adams University). The radish also sheds leaves as it grows and these leaves become excellent food for worms leading to increased earthworm populations which are highly beneficial.
Daikon or deep till radish offer a very large deep bulb that can puncture through compacted soils and help aerate dense soils that have poor structure. However they need time to grow and develop their roots and would need to be grown over winter.
Phaceliais very beneficial to insects and bees, being capable of flowering through into early autumn. Phacelia also has very hairy roots that helps till ground and aerate soils.
The use of legumes such as Clovers and Vetch can benefit the soil biota, provide food for insects and create organic matter. However it takes time for the Nitrogen fixing nodules on the roots to develop and fix atmospheric Nitrogen, often the crop is destroyed before this happens.
To get a range of benefits and to manage establishment risks using a mix of species is recommended by most agronomists. As part of our Sustainable Landscape Project we are recommending the following options:
1. Catch Crop or Autumn Mix
Sow by end of August destroy before December
To contain per acre.
1.25 kgs Phacelia
1.50 kgs Oil Radish
7.25 kgs Black Oats
TOTAL = 10.00 kgs/acre
2. Over Winter Mix
Sown by the first 10 days in September but ideally in August. Destroyed in the period between late January and mid-March.
To contain per acre:
10.00 kgs Rye
1.00 kgs Crimson Clover
1.00 kgs Oil Radish
5.00 kgs Vetch.
TOTAL = 17.00 kgs per acre