Impact of hemp cultivation on biodiversity and soi health

At the farm visit in July, entomologist Dr. David George from Newcastle University took us through some suggested ways to measure above-ground biodiversity. We agreed on the following protocol:

• Ideally, visit all sites on a single day. It is important to do these assessments in the right weather conditions - i.e. temperatures above 15.5 degrees Celsius, wind speeds ideally under 5.6 mph, enough sun to see your shadow, not raining
• Walk along field edge (ideally a path that transects the centre of the field)
• Measure a 20 metre length
• Starting at 2 metres, stop and record the number of insects in a 1m2 area in front of you, and where possible, categorise these into groups, e.g. bumblebees - pollinators, other bees - pollinators, ladybirds (adults) - predators, ladybirds (larvae/pupae - predators), dance flies - predators, etc. (full list in the guide in the Documents section of this page). It is useful to be familiar with larval/pupal stages of certain species such as ladybirds and hoverflies - common predatory insects.
• Do the final count at 18 metres.
• To maximise the reliability of the data collected, repeat this exercise four times. Statistical power increases significantly from three to four replications.

The group met at the farm at East Yorkshire Hemp in early July for a day of training. They also had the chance to visit the processing facilities, where the hemp is turned into fibre and the remainder is pressed into briquettes for fuel.

Lynda Deeks, soils researcher at Cranfield University, took the group through a 5-step guide for farmers/land managers to measure soil health, where each category receives a score, then tallied up for a final soil health score.

We undertook the assessments at the edge of a field as the hemp had grown tall so access to a more suitable spot for soil assessments was limited. However, the assessments will be done pre-sowing and post-harvest so a proper sampling procedure can be followed. 

The group were trained on how to go about selecting sampling areas. When you select your sample area, have in mind the following:

• An area that is not too large but is representative of the field
• An area where the crop is uniform
• An area within a single soil type
• An area of uniform slope gradient and slope direction
  If you have access to a GPS device use it to record the location of your sample area so you can return to these points later. Otherwise mark the area on a map. If practical also mark the corners of the area in the field with something like a flag or spray paint.
• The comparison (control) plot/field should be of the same soil type to the trial plot/field and adhere to the above criteria.

For soil carbon samples:

• Samples will be collected at random points across the representative sample area following a standard W shaped pattern of sampling. At each point on the W, collect a soil sample, meaning a total of 5 random soil samples will be collected across the area.
• Ensure a sampling depth of 0.3m (0.0 to 0.03m depth) where soil permits - this is best done with an auger but can be done using a spade. 
• Make sure the soil sample face is vertical, so that you are collecting the sample amount of soil across the soil depth.
• Place all soil samples into one clean bucket. Once all 5 samples have been collected in the bucket,
  mix the soil together thoroughly to form a composite soil sample.
• Remove all roots and plant material; scoop out approx 300g of soil and place in the bag to send off for analysis.

Other soil health samples:

• Return to three of the points on the W sampling area that you used to collect your soil carbon samples from. Be careful to avoid where you previously disturbed the soil. Undertake the assessments as described above.

The following measurements will be taken on site by each farmer:

SOIL (change over time, before planting and after harvest)

Soil organic carbon (SOC) - using NRM's Soil Carbon Check service, sampling kits will be sent to the growers. They will collect 5 random samples at 0.3 metres deep across the representative area following a standard W pattern of sampling and send these off to NRM labs for analysis

Soil structure - using the visual soil assessment (VSA) which includes a range of soil properties (soil texture, soil structure), three random sampling points will be chosen within the representative area (coinciding with the SOC sampling points). Infiltration will be assessed using the single ring falling head method, to understand the main drainage and aeration channels through the soil. Three infiltration measurements will be taken at three of the VSA sampling points.

Soil biology - earthworm counts, including midden counts as a surrogate to indicate anecic earthworm activity. The group will follow AHDB's GreatSoils 'How to count earthworms' guide. All middens within a 1 metre radius of the VSA sample point will be collected.

NUTRIENTS

Crop biomass - assessments of post-harvest biomass remaining in the field to understand nutrients available for next crop. This will be collected at the same sampling points as the SOC assessments and sent off to a laboratory for N,P and K assessments. NB: Laboratories require a license to handle hemp. 

BIODIVERSITY

Above-ground biodiversity abundance - a simple walk through fields, counting and categorising insects, particularly pollinators or predatory insects, including larval/pupal stages.

Below-ground biodiversity = soil biology as above

This group comprises 5 licensed hemp farmers, spanning the UK from Jersey to Northumberland. Some of these are long-term hemp growers whilst others are planting for the first time this year. These project partners act as regional representatives within the UK for the first Innovative Farmers x British Hemp Alliance (BHA) Field Lab. The group are looking to participate in sampling and conducting on-site monitoring in order to produce more data on factors which are anecdotally known to be positively impacted by hemp cultivation, such as soil health, carbon sequestration and ‘biodiversity net gain’ and start to produce evidence of this impact.

Whilst the benefits of this crop are widely celebrated and offer huge potential opportunities for a “new” cash crop for British farmers, enhancing the supply of local protein, textiles and construction materials, there is little evidence available publicly to support the theory within the UK. 

As the UK is transitioning from the EU CAP into the new Environmental Land Management scheme, the group want to represent the interests of hemp farmers and the potential correlation with ecological improvement. The considerable gap in scientific knowledge specific to UK hemp is hindering the UK hemp industries ability to lobby for better recognition of this crop’s potential in the sustainable soil and biodiversity arenas. Hemp is still classified as a 'controlled drug' in the UK and the farmers in this group have successfully navigated the current barriers of the ‘controlled drugs’ classification for low-THC Cannabis Sativa.