Devon silvopasture network

In September members of the Devon Silvopasture Network spoke at a very well-received session at the Agroforestry Show. You can watch the session here:

Cows and Trees session at the Agroforestry show

Dr Carmen Segura-Quirante updated the group on the baseline soil sampling results which were taken between Dec 2020 and Feb 21:

·       Different protocols and tests have been followed to determine physical (bulk density and texture fractions) and chemical (pH, % SOC and TN) soil properties

·       Bulk density analysis (BD) and chemical analysis were carried out in North Wyke, and texture fractions were provided by an external laboratory from baseline soil subsamples processed at North Wyke

·       Estimated time effort in working hours for the baseline soil study =2000 h. Lab team= 8 people

·       Tests to check the presence/absence of inorganic C (IC) were based on acidified washing procedures of soil subsamples when pH > 6

·       We assume Soil Total Carbon (IC + OC) = Soil Organic C as no evidence of IC was found (pH < 6 in most of the samples and no effervescence when higher pH)

·       The composite sample approach is an accurate method to determine SOC at baseline level. In our case 1 composite sample= 6 samples from the same strata and per depth. To do the composite sample, we took a subsample of each individual sample to keep spare soil in our archives for the future.

·       SOC and TN (%) were determined by standardized and recommended methods to assess changes in SOC (Carlo Erba elemental analyser)

·       SOC stocks were calculated from SOC (%), BD (g/cm³) and soil depth (cm) for 0-10 cm and 10-30 cm soil depths

·       Mean values (% SOC) in the topsoil (0-10 cm) were in the range of values reported in the UK for arable fields and grasslands

The individual results will be sent out to the farmers themselves shortly.

The next samples will be taken within 4 years of the initial samples by Rothamsted.

We have pending to pass the questionnaire about land use and management to them.

Rothamsted research visited the farms in February and March to undertake baseline sampling and will monitor the change of this over the next 12 years to understand whether the integration of trees improves soil organic carbon sequestration and soil structure.

The assessments:

• Soil organic matter - leaf and root decomposition, root respiration and root fungal/bacterial processes all add organic matter to soils
• Bulk density - a measure of soil compaction, which influences water availability, plant rooting depth, the availability of plant nutrients and soil microorganism activity
  
  The samples are being frozen and stored - in total around 1,000 samples have been taken. Samples will be taken at 0-10cm and 30cm. Sampling will next take place at intervals over the next 12 years, with the next soil sampling to take place in 3 years time as changes in soil organic carbon is a slow process.
  
  The researchers expect that there may be some initial losses in soil carbon from tree planting, but overall this is minimal as soil disturbance associated with digging small holes for the trees is likely to be very low.
  
  The researchers followed sampling methodology followed UN FAO protocol for measuring, monitoring and reporting on soil organic carbon in agriculture. The protocol can be adapted locally to monitor SOC stocks and stock changes to support management decisions and can be found at: http://www.fao.org/3/cb0509en/cb0509en.pd

Advisors from the Woodland Trust and FWAG visited each farm in autumn 2020 to develop tree planting designs unique to the needs of each farmer. The trees (funded by the Woodland Trust) were planted at the farms throughout February, with some farms involving dozens of local volunteers in the planting.

Three planting designs will be used overall - shelterbelts, regular spaced strips and open-grazed clustered wood pasture. The farms will use one or more of these designs across their fields. The benefits and drawbacks of each design are detailed here. 

For example, regular spaced strips allow machinery access to alleys for cutting silage if farmers wish to manage this as productive grassland throughout the year. However, the prioritisation of grass in this design means the least biodiversity benefits are expected of all three designs.