Alternatives to plastic film mulch

There were more growers interested in the trials in the second year.  These included:

• A fruit tree nursery and market garden open to all mulches
• A grower in Scotland under tea plantation and a large orchard mushes using sheep fleeces
• Farmer with small Dexter beef herd in Essex interested in using sheep's wool
• Gibside veg growers using a range of mulches
• Market garden in a women's prison in Surrey, currently trying to phase out Mypex, will try biodegradable vs mypex vs cardboard and straw
• Agroforestry tree fruit nursery, creates woodchip from short rotation coppice sourced on-farm, concern of biodegradable mulch is that it is not permeable so will need irrigation.

These growers took soil samples to see if any microplastics or plasticisers were released into the soil from biodegradable and non-biodegradable mulches. 

Current practices of the new growers:

Gibside community farm primarily grow under biofilm mulch.  They carried out a trial comparing leeks under woodchip and biofilm mulch and found no difference. They think using mypex to keep weeds down before crop has established, then removing it, could be a good option. Would like to trial green manure particularly on brassicas. Tried small clover and some vetches as a living manure.

A recommendation from the kale grower is to try it on a single harvest crop, otherwise data collection takes a lot of effort!

The tea grower planted tea bushes in 2017 and is primarily interested in using sheep fleeces. They have a 5 acre orchard. The benefits of wool are that it is a slow releaser of nitrogen, it prevents runoff, holds water, preventing the soil from drying out, and it insulates soil. Tea plants need very high levels of nitrogen 

Garden Organic will perhaps try biofilm and straw.

Sue Johnson - kale, celeriac, tomatoes, lettuce - would like to try sheep's wool if she can find a source of it.

Francis at CAWR says: "We have only made some preliminary tests so far but we have found a big range of potentially harmful chemicals in the commercial paper mulch that Anton used - I think these may come from the waxy coatings they give the paper to make it more durable. This is not to say that these are actually released into the soil at detrimental concentrations but it is interesting to note that paper is not necessarily better than plastic in this regard."

The blackcurrant grower from the previous year's trial will continue with the trial.  He is keen on testing out logistics of how you lay woodchip on a field scale using a sileage feeder. He has found someone who would lend them one. He also wants to try and increase the water level under the woodchip. The blackcurrant grower's issue of rolling out at scale was also identified in the apple scab field lab he took part in.

Tom Appleman and the blackcurrant grower are both interested in looking at how woodchip will impact soil nutrients. 

Andrew Adams at the prison trial site is growing potatoes, courgettes and onions this year.  He is using three mulches.  He is also growing chillies in glasshouses and will do some mulch trials in those including cardboard (as its a waste product on site); woodchip or straw; biofilm and mypex.

This year there has been very little interest in biofilm amongst all growers, and more interest in using on-farm, loose, available mulches. The blackcurrant grower will continue to use biofilm, but since he knows what it does (because it behaves in the same way as a conventional plastic) he has no need to trial it.

His observation is that “drip line with laying biofilm is phenomenal as they have a microclimate there and they are 1 year ahead in growth than other blackcurrant growers.”

Reflections and results from first year of trials

The majority of quantitative data from this year has now been collected. This, alongside qualitative information on growers' observations/experiences, suggests:

• There are range of viable alternatives to plastic - both local and commercially sourced, that can reduce the need for weeding
• It is not possible to draw conclusions on individual mulches or compare results between farms as a wide range of crops, soils and mulches were trialled. 

However, there were some common observations:

• Most growers reported difficulty with biodegradable mulches tearing and disintegrating or detaching from the bed; if weed growth cuts through the film, this results in excessive weed growth
• Unsurprisingly, un-mulched plots performed the worst in terms of yield and weed coverage
• In the loose mulch trial of six on-farm materials, including poplar chips, extruded poplar, willow chip, hay and grass cuttings, the weeds got out of hand except in the hay treatment - this was the best for suppressing weeds by far.
• Woven polyethene film disintegrated quickly after harvest

• All the black mulches effectively suppressed weeds
• Loose mulches need to be applied at a high rate.  Combining loose mulches may work better, for example, one grower reported a layer of hay with a layer of brown paper underneath worked really well. It is suggested that a material like paper or cardboard should be placed underneath to keep the light out, and another mulch on top for organic matter additions.
• If using woodchip, the choice of wood is important, otherwise the plant may experience mineral/nutrient deficiencies. Irrigation is also important.
• The un-weeded plots didn't do as well as the mulched plots, which seem to have kept the water in.
• CAWR trials comparing poplar chips, extruded poplar, willow chip, hay and grass cuttings found that the hay was by far the best at suppressing weeds. They didn’t experience any issues from the hay mulch seeds germinating
• CAWR found a big range of potentially harmful chemicals in a non-bleached paper manufactured for no-dig organic production. It is not known whether the chemicals leach into the soil or what their effect is.

 Other findings

The blackcurrant grower hopes to use woodchip as a mulch as they have access to willow and spruce on farm, though the amount of willow woodchip required to scale this across the farm is a potential barrier.

The blackcurrant grower has been chipping willow on-farm as a mulch. "It raised more questions than answers but we needed to look at crop vigour so after some months started counting the number of branches". Greater vigour with potato starch but higher number of deaths and dwarfism amongst the bushes.

Large woodchip - bushes grew bigger but with less vigour than biofilm. Could be because the dripline was set up for the biofilm and the ones under the woodchip might have just been thirsty. it barely rained in May and June so they fully relied on the drip. where the biofilm ripped, the cuttings were subsumed with weeds.  They need to repeat the trial again to check the water is there for the woodchip.

Another problem is the logistics of getting 20 thousand cubic metres of woodchip onto a field (which is needed for 24 acres of blackcurrants). The logistics of doing their own woodchipping and spreading on-farm is the barrier to doing it at the scale of their farm. It's not impossible - if there was a very clear benefit of doing woodchip, we could change the whole ecology of the farm to do it.

The potato starch is something we know how to use - if there was a buying group to reduce the cost by buying in a large enough quantity of the film, that'd be the way to go.

Sue Johnson - layer of hay with a layer of brown paper underneath worked really well. Paper rotted under the hay but the hay stayed there and kept the weeds down.

Anton has been coordinating garden organic members' trials - 70 completed results returned.  These trialled weed fabric, bioplastic mulch, and paper mulch on small scale plots growing onions over summer 2020. These trials saw a yield increase of 10% across all mulches; paper mulch was quickest to break down; bioplastic mulch was difficult to work with and there were concerns over the energy used to make it; paper mulch was the most popular.

The field lab will continue into another year to allow growers to run trials who had expressed interest but were not able to take part this year. This includes growers interested in looking at wool as a mulch..

More information on this field lab, including individual grower data and a video of the trial, can be found in the reports and results section of this field lab page. 

Trial details

Trials this year are taking place at 5 sites.

1) Onion trial at a community farm in Warwickshire, recording yields and weed coverage. This site will compare an unweeded plot with no mulch, a weeded plot with no mulch, and plots of either woven polypropylene, polythene, paper or commercial biodegradable films.

2) Kale trial at a market garden in mid-Wales, recording yields, costs, weed & pest damage. This farm will trial compare biodegradable film to grass cuttings, woodchip and an undersown living mulch.

3) Blackcurrant bush trial at a commercial farm in Essex, recording growth of new bushes planted into the mulches, the number of dwarf and dead bushes and weed coverage. This farm will trial out biodegradable film and willow woodchip in two sizes compared to a unmulched bare earth.

4) Organic farm in Leicestershire, comparing cardboard, hay and grass clippings.

5) Organic community farm in Newcastle-upon-Tyne, comparing woodchip, woven polypropylene and biodegradable film.

Unfortunately, although ten growers initially signed up to the trial, several growers had to drop out due to the impacts of Covid-19 on, slowing the delivery of mulches, hindering some people's ability to get out on site or have colleague support to run their on-farm trial. These will have the option to commence their trial in the second year of the field lab.

Protocol pack – how to run your own trial

Instead of physical workshops to help instruct the group on data collection and mulch laying, the researchers and coordinator have created a how-to guide and an instructional videos.  If you are exploring non-plastic mulches and would like to follow the protocols of this trial, longer versions of these can be found in the knowledge hub section of the website.  This includes tips for laying biodegradable mulch.  A shorter version is below.

Trial Design

A range of different mulches will be compared to plastic film/ standard practice including biodegradable film; woodchip; hay; grass cuttings; cardboard; paper and straw.

Trial Layout

For each crop you are testing arrange the ‘plots’. If you have the space and time to repeat the layout more than once (known as a ‘replicate’), it will make the data more robust but additional replicates are optional.

• Test plots should be at least 20m long, if practicable
• Treatments can be arranged randomly within the replicates
• The timing of mulch application should be according to normal practice

Assessments – Required

Weeds

• Monitor weed burdens once a week (This could be reduced to once every two weeks at less critical stages of crop development e.g. after canopy closure of leafy crops)
• For each strip visually estimate % weed coverage at 5 points along the strip.
• Take a photograph of each assessment/ data point and email to CAWR. This will enable researchers to account for differences in perception between individual growers

Yield

At the end of the growing season record the total yield in each plot

Qualitative/ Visual observations

At same time as assessing weed burdens, record any general observations of interest. For example, ‘serious slug damage’, or ‘the crop under mulch x seems to be developing faster than under crop y’

Costs

Throughout the trial record any costs, for example:

• Purchase of any mulch materials
• Preparation of mulches (e.g. wood chip/ grass clipping)
• Labour involved in laying mulches
• Cost of supplementary weeding

Assessments – Optional

Soil Conditions

• If you are working with several crops choose one to monitor. If you have several replicates, choose one replicate to work on
• Place a temperature probe in the centrifuge tube provided
• Within your chosen crop/ mulch combination, bury the tube in the centre of each strip. So if you looking at biodegradable film and woodchip on cabbage, place one probe in the plastic/ current practice strip; the second under the biodegradable film; and a third under the woodchip.
• Follow the instructions inside to set them up to record every 30 minutes - if you just bury them as received, no data will be collected! The probe will automatically record temperatures and store the data on its internal USB drive.
• Retrieve the probe at the end of the season

Soil Nutrient status Pest and disease damage

Before the mulch goes down and again immediately after it come up at the end of the season, for each strip:

• Take 15 soil cores along the centre line
• Bulk these 15 samples together in the plastic zip lock bag provided
• Label the bag with: Your business name; the crop; the mulch being tested (including the plastic/ control mulch); and the replicate number
• Fill in the NRM sample analysis request forms provided
• Place all the bags in the preaddressed box(es)
• Send the boxes off (postage has been pre-paid)

Pest and disease damage

At same time as weed assessments score damage severity from 1 – 5 and record different pest species/ diseases if you can identify them. AHDB Horticulture are particularly interested in downy mildew on onions.

Crop development

At fortnightly intervals record the stage of the development of the crop in each strip.

Soil microbial activity

At harvest, use the Solvita testing kit provided to assess the level of microbial activity. Step by step instructions will be provided with the kit

Earthworm counts Summary of data collection activity

At harvest, assess the number of earthworms under each strip using the AHDB: How to count earthworms protocol. 

Planning the Trial

Growers, gardeners, mulch suppliers and researchers met at Garden Organic to agree on the objectives and methods for the trial. There was a wide representation of growers, including (soft fruit) crops; field vegetables; small-scale farms and protected cropping.

The group discussed the following:

• The type(s) of mulch to trial - each farm will decide on which mulches they would like to trial, but they include compost, woodchip, starch-based materials, hay and cardboard
• The size of the trial area - ideally 20-30-metres strips, replicated in several growing spots to generate meaningful data (less for small farms)
• When the mulches should go down - this depends on the mulch and crop
• What, data growers can/want to collect - the priorities are weed cover, crop performance and pest damage (measured on a scale of damage), but where possible, the growers would like to also consider soil moisture, and soil health (most likely via a low-cost solution such as a worm count). Cost and time will also be considered in the final results.

Launch meeting at Ryton Organic Gardens