This field lab aims to investigate the potential of living mulches within annual arable crop production as a means of achieving organic and low-input no-till systems. Two key services that need to be delivered for agricultural systems to function productively are weed control and nitrogen supply. Non-organic systems rely heavily on costly herbicides and artificial fertiliser, whilst organic systems need an effective alternative to chemical inputs and a way to reduce tillage.
With environmental sustainability in agriculture under increasing scrutiny, there is a drive for finding alternative options to the current systems. The use of (semi) permanent clover groundcover, also known as a living mulch, may provide an opportunity to provide key agricultural services and remedy some of the current environmental concerns.
The trial design has a living mulch and control strip present within the same trial field. The trial mix is a 70:30 combination of small leaf and medium leaf clover. The trials so far have tested winter oats and rye as cash crops in the living mulch.
Assessments were carried out across nine farms over three growing seasons to determine the field performance of the cereal in the mulch and then yield and quality data was collected at harvest. Soil samples were also taken in the Autumn.
From assessments in the three trials where the living mulch established, there has been a significant yield gap from implementing a no-till + living mulch system, averaging around 60% yield compared to the control (standard farm practice). Results suggest half the yield penalty comes from implementing a no-till system, with the rest due to clover competition. These comparisons were enabled by one site having three treatments: 1) Control; 2) Direct Drilled without clover; 3) Direct drilled + clover living mulch.
The farmers can tolerate some yield penalty as there are savings in cultivation costs and reduced seed cost as there is no need to sow annual cover crops, plus there is increased forage for sheep.
Two caveats to the yield results are that 1) the mulch was supposed to be predominantly microclover but in practice was more of a standard medium leaf, which provides more competition with the cash crop. Some of the group are now trialing a smaller leaf variety. 2) Minimal intervention was applied to the clover during the growing season. Clover management is also being investigated in the next round of trials.
18 months since the clover living mulch was drilled, levels of available soil mineral nitrogen are rising, with statistically significant results. In the living mulch plot, available nitrogen is over double that of the control plot (standard farm practice). However, we cannot yet assume it can be a proxy for N fertiliser replacement.
There have been significant increases in the relative abundance of perennial weeds and grasses under the living mulch system. Mechanical control and ploughing helped to reduce weeds in the control plot.
There is evidence in literature of other long-term benefits of a no-till living mulch system which cannot be addressed in this field lab. This includes soil fertility and biodiversity.
Four new farmers have joined as triallists aiming to establish a clover living mulch in the autumn. All trials are using either a trial mix of 70% Jura and 30% Merwi, or 100% Jura (micro clover). Further details:
Update on spring trials:
James Alexander: Will continue with organic trial another year, drilling spring beans into the mulch and controls. Whilst establishment in the organic field has been successful, the second attempt to establish clover in the conventional field has failed.
Mark Lea: Has terminated two previous trials due to his own rotation and issues with perennial weeds. Set up a new mulch trial in Spring 2021 undersowing spring wheat and including a non-mulch control. Is thinking about testing both heritage winter wheat and winter oats again. From a trial perspective having a second year of winter oats would be valuable and could help inform on management practices for mulch control.
Jamie Stephens: Has a successfully established clover mulch established in Spring 2021.
A summary of the results is below. A full final report can be found at the reports section of the field lab page.
Results so far have found an average yield penalty of 30% in the living mulch compared to the control. There is also a move towards more aggressive perennial weeds in the living mulch as well as more grasses compared to broadleaved weeds.
However, with increased clover cover in the second trial year, overall weed cover was reduced in the living mulch system. There are also several soil health benefits in the living mulch system, with significantly increased available nitrogen (as seen in the graph below) and earthworm counts and a trend for increased microbial activity and soil organic matter.
There are several less easily quantified benefits to the system; reduced tillage, lengthening organic rotations, opportunity for reduced artificial inputs, and reduced leachates and run-off. Grazing can be beneficial for reducing the weed cover and clover control at key points of the growing season. The use of strip tillage, inter-row mowing or crimping where the system allows, can knock back the clover and reduce competition with the cash crop, although these technologies can be expensive and are not yet widely available on the market.
Mark Lea, trialling living mulches on his organic farm in Shropshire, shared the changes he'd make in the following years:
On a practical level, the living mulch setup has worked. The main disadvantages of the system Mark has noticed so far are:
Yield penalty (the clover provides too much competition). There are some financial savings (lower cultivation costs, forage value from grazing, potential to remove the fertility building period). "We know we can live with 0.6 tonnes/ha reduction in yield without being any worse off, purely in terms of cost saved... that is before the non-costed benefits like carbon sequestered, improvements to soil heath and structure". They will continue to explore ways to reduce the clover's competitive edge, e.g. interrow mowing
Less control over perennial weeds. As an organic farmer, ploughing has kept weeds to a 'reasonable' level, but in these trials, no-till + living mulches has seen a build up in grass weeds, docks and thistles. There may be a need to periodically break the living mulch cover to plough for perennial weed control.
They tend to run a five year rotation, where one year is a fertility building grass ley with clover + four years combinable crops (inc. a legume). Realistically, Mark thinks he might be able to have 2 x 2 year periods within the four years of cropping that involve a living mulch. Between those, they could break the clover to control the perennials. This setup wouldn't typically be possible without the living mulch - "the whole system of nutrient budgeting could change" if clover is in the ground every year for the cropping period.
James Alexander, Oxfordshire:
Direct drilled winter oats into the clover in Oct 2020, planted in 20cm-wide rows. Currently the oats on the organic plot are looking better. “The oats stood proud over the clover all winter and those crops grown in the mulch are looking taller, darker and stronger than our farm standard, due to improved nitrogen fixing”.
Jamie Stephens, Worcestershire:
Ploughed in February 2021 to remove the weeds before reseeding the mulch, which didn’t establish in the first year. This will be accompanied by a nursery crop of oats to aid clover establishment.
A separate plot of medium-leaf clover has been planted to provide extra competition against weeds and to promote sheep grazing throughout the autumn and winter. Sheep grazing over winter should help to limit the clover’s growth if it is outcompeting the cash crop, and in turn stress the clover, which releases nitrogen into the soil. He has also adapted a CTM weedsurfer to interrow the living mulch when grazing would otherwise damage the main crop.
Clive Bailye, Staffordshire:
Reseeded mulch this spring, interrowing it with a barley and wheat crop.
Mark Lea, Shropshire:
Two trials - winter oats and winter rye this year - the clover is doing well but too much competition will result in yield penalty. The clover is providing good control of annual weeds but not perennials. Mark is considering drilling the next crop earlier (i.e. Sep rather than Oct) so that the crop has more time to establish.
Given the risks of spring drought which has caused several cases of failed clover establishment amongst the trials, the group will look to potentially run complimentary trials on autumn establishment of the clover. Based on indications of high competition from the clover, we discussed that sites without livestock should perhaps sow only smaller white clover variety, whilst sites with livestock that can provide heavy grazing may be more suited to the current mix (70% small-leaf and 30% medium-leaf).
James Alexander, Oxfordshire (conventional and organic trials):
In spring 2020, James drilled 3ha of clover directly into both an organic and conventional spring barley crop using a Horsch drill. The clover established very well on the organic land, not exceeding more than 7.6cm in height and didn’t cause any issues at harvest. Weeds appear to have also been suppressed. There was a slight increase in barley yield which may have been due to the extra nitrogen supplied by the clover. The conventional trials didn’t establish – they were planted with the same drill on the same day.
Jamie Stephens, Worcestershire:
The first year’s mulch didn’t establish, due to drought conditions, which brought a strong emergence of ryegrass and other weeds. The plan is to plough to remove remaining weeds and reseed the mulch this year.
Clive Bailye, Staffordshire:
The clover was interrow drilled into a wheat crop over a 4ha area. Very dry conditions (no rain for 90 days straight) meant that none of the clover established. Reseeding mulch in spring 2021.
Mark Lea, Shropshire:
The clover was undersown in early May 2020 into spring wheat and winter wheat fields. The following period of very dry weather resulted in poor clover establishment. Stubble was grazed back hard by sheep until late October then new cereals (winter oats and winter rye) were disc and tine drilled (to compare drilling). In the winter rye field, the clover has done very well and the rye is 'okay'. In the winter oats field, both the oats and clover are doing well. Both drilling methods appear to work.
The group met virtually in late September to discuss the initial results from the 7 trials:
Because of this, the group of triallists falls into two categories:
1) Successful clover establishment in Spring/Summer. Next phase is drilling cash crop into standing clover
2) Unsuccessful clover establishment in Spring - needs reseeding
Potential reasons preventing establishment:
Impact of clover on weed cover:
The farmers discussed establishment of the white clover living mulch. They reported mixed success so far, which is particularly impacted by the dry weather:
The group have undersown the living mulches into winter and spring wheat. Warm weather from mid-March meant that some farmers decided to undersow the mulches as early as possible, to avoid too much cover from the winter wheat. Others sowed in mid-late April, hoping for a period of rain.
The dry weather has caused some concern; the lack of rain has meant that the mulches haven't yet emerged at any of the farms. "Moisture for a few days after sowing and an occasional drop through the summer seems to be the crucial thing", one farmer commented.
Areas of debate amongst farmers in the trial:
24 April 2020
25 June 2020
10th November 2020
14th May 2021
17th June 2021
12th August 2021
15th September 2021
Bristol / UK-wide
Arable & Soils Advisor at Soil Association, and farmer. I ran the family farm in Devon for 25 years, farming dairy, then organic beef, sheep and arable units with holiday cottage conversions. Former chairman of a local farmer owned co-op grain store, and involved in the grain supply chain nationally.
Chipping Norton, Oxfordshire
Green Acres Farm
Organic Research Centre