Does extended pasture resting after grazing improve soil microbiology and soil health?

The group met in September at triallist Dan Gammon’s farm for a catch up and discussion.  It was a tricky spring which meant that some of the trial plots had to be grazed harder in April due to drought and lack of grass, and some were then damaged by the wet weather.

The trial has highlighted the lengthy timeframe required for improving soils:  changes to soil biology and organic matter happen over a long time period, and you cannot expect big changes very quickly.  So if you’re trying a new management technique like this don’t be disheartened if there’s been limited change after a few years!

In the main the trials are going well, here are some interesting outcomes from the group meeting:

Milk Yield

Milking has been fine on long grass: no drops in yield at any of the trial farms who were represented at the meeting.  However, on one farm the herdsman had trouble with the milking, as the cows were filling up on the long grass in the trial plot.  Then after milking they were not eating their next allocation as they were so full. They’ve split the grazing now so they’re grazing 1 night and 1 day on the tall grass which has helped this situation – but its something to be aware of if you’re trying this.

Soil

The group dug a soil pit in Dan’s trial plot.  The soil structure scored really well (1 on the VESS scale), lots of earthworms (12), and really good dense root matter. 

The soil pit in the control field also scored 1 on the VESS scale and and had a high number of worms (20) but the roots were not as dense as in the trial side.  This might be because the trial field was put to standing hay last year, or it might be because leaving the sward for longer allows it to put down more roots between grazing. 

Those farmers who are trialling the practice on their already good fields have found that the practice has accelerated improvement.  It has taken longer to kickstart the improvement on the poorer soils.

The group looked at soil samples under the microscope.  Anecdotally they saw more organic matter and fungi in soil of trial plot, but this has not been tested in the lab yet.  The group are waiting as long as possible before sending samples to the lab ato maximise the time over which change can happen.

Dan noticed that on his treatment side the cow pats were broken down more quickly and there was more surface fungi around cow pats than on the control side.  This may suggest more active soil biology or more moisture levels.

Ground cover

The group noticed that the treatment had very good ground cover which kept the soil moist, whereas the control growth was more open, so more at risk of drying out. A denser root structure and higher soil moisture creates a more resilient sward.

The group

Matt Preston has won Grassland Farmer of the Year Award!

British Grassland Society competition

Dan is extending the practice of letting the grass grow longer before allowing the cows in beyond the trial field: he finds it is working for him in terms of grazing management.

The group really value the benefits of a specific grazing discussion group and the sharing or knowledge and experience, as well as the group dynamic to encourage them.

Next steps

• November 23: Milk yield round up and agrinet round up data available
• Spring 2024: farmers will carry out forage sampling on second graze
• Summer 2024: Plan to do an open on-farm event with session by Farm Carbon Toolkit
• Autumn 2024 (or maybe spring 25) frull soil tests for organic matter

A dry spring:

Like many livestock farmers, the group had a challenging spring with prolonged dry weather significantly impacting grass growth, so after an initial graze in early spring, second grazes have been after a much longer round.

The group receive training on optimal grazing height:

The group gathered for a webinar with Siobhan Griffin of Next Level Grazing, who has been mentoring some of the triallists as part of their training with Arla around regenerative farming approaches. This was to understand her approaches to optimal grazing height and protecting your grazing wedge.

This was a very valuable session for the group and made a number of the farmers aware that they had let the sward grow too high in grazing rounds last year, with too much “brown” growth, impacting on milk yield and ability of the third of trodden sward to break down.

Here are some details of the session on the IF website: https://www.innovativefarmers.org/news/how-to-build-a-more-resilient-grazing-operation/

Groundswell Session:

There was lots of discussion around the trial at Groundswell. Dan presented as part of a SA led session on Farmer-Led Solutions to Underperforming Fields & Marginal Land (you can watch the recording on youtube by clicking on the link). Tom and Debbie discussed the trial in a session led by FAI on regenerative grazing for dairy.

Next Steps:

The group needs to come together this autumn to discuss any soil and forage data we want to collect and confirm approach to forage sampling for spring 24 so everyone is prepared to collect samples at the same time and agree on analysis. The group meeting will also be used to discuss how the 2023 grazing season has gone more generally.

Farmers from three of the trial farms met with coordinator Kate Still and Becky from Farm Carbon Toolkit at Old Burford Farm last week to catch up on the progress of the field lab.

We first looked at the progress of the trial plots over the grazing season, and the experiences on the different farms. It was agreed that the severe drought over the summer had made for a difficult grazing season, though in general the trial plots performed well.

• On one farm the control plot was slightly ahead earlier in the season but now there has been some rain it appears that the trial plot has taken over, and they have pretty much levelled out.
• On one farm the trial plots seemed to run out of steam towards the end of the season, while the control kept growing back, this was potentially due to control being a more diverse sward
• There was no loss of milk from grazing the trial plots at the end of the season for two of the farmers, though a third reported a slight reduction in yields.
• There was a feeling that you can get away with moving the mob less on the higher plants.
• In theory the cows should spend less time grazing the longer grass as they can take larger mouthfuls.
• Some farmers didn’t achieve the trampling effect in the mob paddocks they were hoping for, perhaps need to stock higher

Sward Quality

• One farmer said he was impressed by the quality and quantity of clover on the trial plot compared to the control in the second grazing.  
• Another triallist found that there had been a problem with docks growing in the trial field.  
• He also found that the chicory grew up and shaded out the smaller herbs around it, leading to more bare ground in the field than he would have liked.  “The cows didn’t really like the chicory anyway”.
• One of the triallists had previously found establishing sainfoin more challenging as the large seed size meant it had to be drilled separately. He then found it not to be very persistent
• By the end of the summer two of the triallists found that the trial plot had large amounts of dead grass and chicory stalks lying on the ground which don’t seem to be breaking down – one said “it feels like there is a lack of complex soil biological processes helping it break down”.  This could have been due to the drought and high soil temperature:  Becky explained that the dry season had a massive impact on soil biology, partly because the earthworms were driven so deep underground to find moisture.  As a positive, however, it was thought that this dead matter would have protected the soil during the extreme heat.  Also, one farmer noted lots of mycorrhiza on the surface below the dry grass, because the lignified stems help feed the fungi.  
• One farmer hoped that “Mob grazing will really improve wildlife” and that it would be especially good for nesting birds and bee populations and other pollinators by providing a more steady nectar source.

Soil Test Results
The results from the initial soil tests were then discussed, and we were lucky to have Becky Wilson from Farm Carbon Toolkit with us to guide us through the baseline soil data.

The soils were tested in May/June 22, the full testing will be repeated in Spring 25. The plots have been GPS tagged so the exact same places can be sampled again next year. In general the statistics showed that there was no significant difference between the soil test results, but this was to be expected at this baseline stage of the trial.

There were some differences which were not statistically significant but which are a good indication of soil improvement during the trial:

• There were more earthworms in the trial plots, which might be because the soil of the trial plots was more shaded during the summer heat so they did not have to burrow so deep.
• There is also an improvement in fungi levels in the trial plots which is a good sign, though any increase in fungi levels would usually take longer.

It is expected that a greater statistical difference will be seen in the next samples: hopefully a further shift from bacteria-dominated soil to higher fungi levels in the trial sites. The next round of soil sampling will include infiltration tests, these were not completed in 2022 due to excessively dry conditions.

Next year when the triallists will be looking at doing some soil assessments themselves, including worm counts, infiltration, VESS and also they are looking to include a dung beetle count in the trial as this is usually a good sign of soil health.

All the triallists started with pretty good soils, but because they are so varied the group discussed how to ensure they can produce useful and robust outcomes.

A look at the Trial plots

The group then braved the elements and went to look at the trial plots.  The soil in both control and trial plots was still very dry below the first few inches from the drought, despite the driving rain on the day.  It was felt to be a good sign that three worms were found in the soil in the trial plot and none in the control!
Overall it was a very successful gathering, and reinforced enthusiasm in the group.

This trial is looking at both the rest period of the sward (e.g. effect of tall grass), and the incorporation/length of residual as part of grazing strategy as both of these are thought to have a positive effect on soil health. Leaving higher residual allows for continued photosynthesis and root structure, whilst trampling adds nutrients to the soil.

Trials will take place on six farms over 3 years. Trial protocols are as follows:

Split a field or choose two similar soil type fields, with similar sward composition. Restrict choice of field to those that haven’t been cultivated within the last 2 years and no cultivation should take place in the study fields for the next 3/5 years to ensure stability of soil.

Control plot: Manage as routine within the grazing rotation

Treatment plot:
- Aim to allow pre graze sward growth to reach a height 30 – 50% taller than in control field, with an aim where suitable, of an entry cover c. 4500 kg/DM per ha
- Apply a 1/3 eaten, 2/3 residual/trampling approach – with stock removed at a a minimum 7 cm or 2000 – 2500 kg/DM per ha.
- Apply a stocking rate/land parcel size to meet forage needs of group of cows. Treatment and control fields can be split into multiple grazing cells/paddocks depending on size/forage need of the group of stock. The control and treatment paddocks can be grazed at different points within the grazing rotation as long as the entry and exit sward height of the control field is in line with he “standard” rotation and the entry and exit approach of the treatment field is in line with above.

Data already being collected by the farmers:
- Pasture covers (plate meter data) (due to concerns over accuracy of plate meters, especially with diverse leys, farmers will also measure sward height and where possible, cut and weigh a quadrat sample to get accurate kg fresh weight and DM, before the animals go into graze. 

Data collection in April 2022 (Baseline testing) and comprehensive data collection at the end of three grazing periods year 3 (October 2024) as detailed below. Additional physical soil assessments will be completed in 2023 and 2024 as part of field lab meetings. This soil assessment strategy has been put in place to make best use of the budget and in recognition of the slow change in the chemical and biological characteristics of soils.

The Farm Carbon Toolkit will undertake assessments on both the control and treatment fields:
- Soil Organic Matter 0-10cm, 10-30cm, 30-50cm
- VESS Scoring
- Infiltration rate
- Worm count
- Nutrient analysis
- Aggregate Stability
- Bulk density
- Biological activity using soil my undies protocol

For more information about the Farm Carbon Toolkit’ soil testing methodology and these tests, visit: farmcarbontoolkit.org.uk/toolkit-page/measuring-soil-health.

Additionally using SoilBioLab, soil bacteria and fungi lab tests will be completed for control and treatment fields. Baseline samples will be completed in April 2022. Final testing may be completed in October 2025 at the end of the grazing season, but following review, may be carried on in April 2026 allowing for the resting effect of the winter period.

Following tests:
- Moisture Content
- Active and Total Fungi
- Active and Total Bacteria
- Hyphal Diameter
- Organism Ratios

Forage analysis

To understand the impact of changes in soil health and mineral availability there will be the opportunity where farmers can commit to collecting their own forage samples to carry out micro mineral forage analysis twice in the year in the baseline year 1 (2022) and year 3 (2024), with a quadrat being cut pre graze. Standard Forage analysis (NIRS) will be completed by Sciantec.