Like many growers around the country, Richard Reed, host of the AHDB Cereals & Oilseeds Berwick-upon-Tweed arable Monitor Farm, is asking whether cover crops can help him improve his soil health.
This year he has tried four different cover crop mixes. The Berwick Monitor Farm group met on 19 January to discuss the practicalities and his findings so far, with expert input from Dr Liz Stockdale of Newcastle University.
Why cover crops?
Cover crops might be the hot topic of arable farming, but growers were encouraged not to follow the crowd without having clear reasons.
“Don’t rush into cover crops because everyone else is thinking about them,” warned Dr Stockdale. “It’s important to think about what benefit you want from them. Predominantly cover crops are being thought of as a soil improving measure, but that can mean different things – soil structure, nutrient cycling and soil fertility, soil organic matter. You might not want them for a soil improving measure at all – it might be for weed control.”
She reminded farmers considering cover crops to first think about the following cash crop.
“You absolutely don’t want to mess up the next crop. Think about how you will destroy the cover crop. Can you rely on frost kill? Will you spray off? Will you incorporate? Would you need to drive on your land at the wrong time?
“Make sure that you use a site-specific crop and management strategy that fits with what you need. Keeping crops growing over the winter is a good thing for soil health, biology and structure and to minimise run off and soil erosion. But how you make that work effectively depends absolutely on your own system – your soil types, the nutrient balance, the cropping system into which you’re incorporating the cover crops.”
Timing your cover
Looking at practicalities of growing cover crops in the north of the country, farmers were reminded to consider drilling dates and the amount of time the crop will have to get established.
In Northumberland, there is a tight window for fitting a cover crop into the rotation, which has an impact on the choice of crops.
“Here in Berwick, the wheat harvest doesn’t often finish until the start of September, so cover crops can’t be established until after that,” said Dr Stockdale. “We’ve seen here that the grass-based cereals and rye-type cover crops establish much more quickly and deliver a much better cover than legumes. So in the north of England we might focus on these cover crops, whereas in the south of England legumes and other crops might be suitable.”
Cover crop trials at Ancroft
At Ancroft, Richard hopes to increase the organic matter and humus to produce better crops and have fields that drain and travel better. Easing workloads and improving timeliness is also a goal for his farm.
Richard Reed sowed four different cover crop mixes on a total of 9ha on 7 September 2015 after winter wheat, to be followed by spring barley. It was all put down without slug pellets. Since 25 December 2015 the farm had had around 7” rain but was holding the water well. The land – heavy sandy loam – was one of the best fields on the farm. The cover crop try-outs are on half of the field, and which includes half of the headland to see if they would help with headland compaction issues.
The cover crop trial mixes were:
Vetch (60%), red clover (20%) and Egyptian clover (20%), costing £80/ha. The clover had all been lost to slugs.
Black oats and vetch, costing £39/ha. The black oats were grown to see if black-grass could be suppressed through allelopathy.
Black oats and berseem clover. Again, the clover had been lost to slugs.
Oil and tillage radish, European oats, phacelia and forage rye, costing £37.85/ha.
Richard plans to spray off all cover crops with glyphosate before drilling, although some of the Monitor Farm group pointed out that this could counteract some of the benefits of the cover crop.
He said: “I’ve learned so far that cover crops can be expensive to grow, and timeliness is key. Where we are up north the window is tighter. We need to focus on what we can grow well to make sure we do achieve something at the end of it.”
Quickly-dug pits under the cover crops showed the group of farmers how the soil was faring.
“It has shown me that where we’ve got a growing root we have increased worm activity and better drainage and it seems that fields travel better. In the spring hopefully we can get on fine and get a good crop established and then be on the right path for next season.”
Later in the year the group will look at harvest results, to see whether there was any difference in the crops planted following the various cover crops.
Nitrogen fixing
With most cover crops in the ground between September and March, the opportunity for fixing nitrogen will be limited. Although root nodules may be present, they are just the first expression of the relationship between the plant and the microorganisms.
Dr Stockdale said: “Beware of people who say that cover crops can fix nitrogen. Especially this far north, there’s not the sunshine to do this. To fix nitrogen in the soil, the bacteria needs sugar from photosynthesis and therefore mostly happens in May and June.”
Farmers can test whether root nodules are fixing nitrogen by cutting a nodule with a sharp finger nail. If the nodule runs red, then nitrogen fixing is occurring.
Improving soil health
The key question, Dr Stockdale explained, is whether it’s worth going through the hassle of growing cover crops. She outlined three key benefits, based on improving soil health:
1) More organic matter inputs because of an increase in the amount of time the ground is covered with growing plants;
2) Increase plant diversity, which provides soil microbes with a healthy, varied diet, and creates different rooting depths;
3) Reduce tillage intensity.
However, cover crops are just one possible tool to fit into a farmer’s workshop. Dr Stockdale acknowledged the challenges for farmers:
“It’s really difficult to balance everything. We need to focus on the whole rotation, and to make cover crops work on a site-by-site basis.”
Experiences in Kelso
One of the Monitor Farm group, David Fuller-Shapcott, farms near Kelso and has a 5ha field with a cover crop mix of black oats and vetch, which will be followed by spring barley using min-till.
“I have heavy clay soil, and I want to find out whether we can use cover crops to remove moisture from a field so that I can then min-till barley afterwards. I’ve tried min-till into overwintered stubbles and that didn’t work.
“I’m pleased I came today. There are a lot of questions – some that got answered today and some new ones asked. But if you don’t question things and aren’t prepared to make changes, then you can’t expect to improve.”
David has served on the management team for two previous Monitor Farms in the Borders. He came to this meeting to learn about soil health.
“The snippets I particularly picked up were about how soil temperature stays warmer under cover crops than bare soil; and that soil nitrogen fixation is driven by sugar and photosynthesis.”
