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Hillmount Farm

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Lessons learnt from NFFN soil/biodiversity/carbon audit

We have been working on a project with the Nature Friendly Farming Network and Ulster Wildlife Trust to provide a farm baseline audit for soils, biodiversity and carbon. This included a whole farm biodiversity assessment, soil analysis and carbon footprinting using Agrecalc. Below is a summary of what we’ve learned so far and what we intend to do as a result. Still processing much of it and the inter-relationships at play, but below is what I've mulled over so far...

1. Our hedgerows are in generally poor condition and need a change in management away from annual flailing towards more rotational cutting. Many also need regeneration through coppicing and gapping up. We intend to start on this straight away with reduced flailing this year and coppicing a number of escaped hedges. We will also start a process of boundary improvement fencing off hedges to avoid over-grazing and allow full re-generation after coppicing.

2. The majority of the agricultural land area has been classified as low biodiversity status as a result of the recent history of management under conacre focused on agricultural output only. However, outside of the agricultural land area there are some more positive signs with a number of ponds, parkland areas, wood pasture, scrubby bits and woodlands providing medium to high biodiversity status. We know we have a healthy frog and newt population in the ponds and th river is home to otter, king fisher, heron, dippers, salmon and trout. The ancient oak/hazel woodland along the river is the jewel in the crown from a biodiversity point of view. Our approach going forward will be to try and increase the biodiversity status of the agricultural land without abandoning its ability to produce food. The principal approach being considered is the integration of trees into fields to expand the area of wood pasture. This will increase habitat for biodiversity, provide shade and shelter for grazing livestock and improve soil function through greater infiltration rates and an improved bacteria to fungi ratio. We will also aim to provide more over winter food and forage for birds through incorporating cereals back into the farm and managing our hedgerows in a rotation.

3. Our soil organic matter levels are really high ranging from 17-33% in the Loss On Ignition test. This has resulted in nearly all our fields being classified as peaty. While we do have some mossy/peaty ground, its only a small part of the farm and most of our soils are a heavy clay loam. We suspect the high organic matter levels are a result of intensive slurry applications over many years, combined with an intensive set stocking system of cattle with poor grass utilisation and a lot of trash trampled into the soil surface. As a result we suspect most of the organic matter is not very deep and near the soil surface, so our plan is to adopt management practices which help cycle this organic matter deeper in the soil. This will be achieved through a combination of pasture regeneration with deeper rooting multi-species swards and more rotational grazing with longer rest periods allowing grass plants to grow to their full potential before being grazed.

4. As a result of our soil organic matter levels, we have an estimated soil organic carbon stock of between 10-19%. Many of our pastures have not seen the plough for 30-40 years and while this has helped the carbon stock the above ground pasture quality is poor as a result of long-term intensive stocking and farm management practices. While we are keen to keep soil disturbance to a minimum in the long term a full cultivation re-seed will help quickly reset some of the grazing fields allowing us to establish a diverse multi-species mix which will cycle the soil carbon deeper into the soil profile, but also produce more quality forage for grazing livestock and increase our in-field biodiversity. So a short-term hit for a long-term gain, as long as we get the management right afterwards. For the silage fields which have seen the plough in the last five years our plan is to over-seed and stitch in clover. This should help reduce the artificial nitrogen inputs required to get a 12t multi-cut silage crop and also address the poor canopy cover of these high yielding PRG swards with 30-40% soil exposure leading to soil and nutrient run-off.

5. Our pH levels range from 5.37 to 6.51. 8 out of the 15 fields were below pH 6 and we will tackle some of these with lime over the coming years. However, this will only be the solution for those fields that are getting a cultivation reset as a result of poor pasture quality and which will then switch over to multi-species swards. Our parkland fields and a couple of other fields will remain as long-term permanent pasture. Given the natural acidity of the basalt in bedrock in the area I’m not sure there is much we can do or need to do to improve pH in these fields.

6. Our phosphate and potash levels are high with 11 fields at Index 3 or above. This is as a consequence of the large amount of slurry spread on the land over the past 20 years. This means our soils will be prone to nutrient leaching and run-off, which is a concern particularly when 11 of the fields have riparian boundaries and two have high risk run-off points with gateways at the bottom of hills running onto a lane. In addition, many of the fields have poor canopy cover/sward density either due to poor pasture quality or due to thin silage PRG swards meaning excessive soil exposure to heavy rainfall events particularly over winter months when there are low grass residuals. Some control soil samples were taken last year at a depth of 6 inches instead of 3 inches and interestingly they came back showing deficiency in P, with indexes of 1, demonstrating again the concentration of soil nutrients and organic matter at the soil surface and not deep in the soil profile. We will tackle this nutrient loading in a number of ways 1) Reducing slurry applications, 2) Increasing canopy cover through sheep grazing of silage swards and stitching in high tillering grass varieties and clover 3) Putting in riparian buffers along field boundaries 4) Increasing nutrient cycling deeper in the soil profile through altered grazing practices that increase rest and plant root development and through introducing deeper rooting grasses and forbs into pastures.

7. From a carbon footprint point of view our kgCO2e/ha is relatively high at 6234kgCO2e/ha. This is due to the intensive land management practices typically undertaken under the conacre agreements, where slurry spreading and silage offtake were the priority in order to comply with nitrates regulations and produce forage to support extended winter housing periods during the year. So, the nitrous oxide emissions from soil because of the high input/high output grassland management are a substantial part of the land’s carbon footprint. However, the most sizeable aspect was the methane emissions from set stocking of 140 dairy beef steers over the summer months. We have already reduced cattle numbers down to a maximum of 35 heifers grazing over the summer months alongside a flock of 100 sheep. And with greater knowledge of our soils, we will now work on an improved nutrient management plan to streamline farm inputs and reduce in particular slurry volumes onto grazing land where P offtake is minimal.

8. From a carbon sequestration point of view the Agrecal results were interesting. The first thing that stood out was that despite entering 5.8km of hedgerows into the calculator the carbon sequestration associated was 0. This is because all the hedges were over 30 years old (most are 150 years old!) and that is the point that the experts believe a mature hedge stops accumulating carbon. So, it looks like hedge regeneration could be an important action not just for biodiversity but also for carbon. However as with everything its all about balance, so we won’t be coppicing all the hedges in one go! But rather will work around the farm ensuring an appropriate balance of mature and regenerating hedge over time. From a soils and forestry point of view it was interesting to compare the two approaches. Our 37 acres of woodland is sequestering approximately 4414kgCO2/acre and our 116 acres of agricultural land is sequestering approximately 906kgCO2/acre. I had hoped the soil carbon sequestration from agricultural land could increase under alternative farm management (mob grazing, reduced tillage etc) but with our soil organic matter and soil carbon levels already so high, perhaps this is not possible and certainly not to the extent of achieving what the woodlands are currently sequestering. As described above it feels the job at hand is to secure the soil carbon we already have in our soils deeper into the soil profile for long term sequestration as currently it is vulnerable when wholly accumulated near the soil surface. And then the focus is really on driving down emissions from farm practices rather than soil carbon as that will be where the biggest impact can be made.

Sam Millar
Apr 03, 2022

We haven't ploughed for 5 years. Roundup (i know some frown upon it) and then power harrow. Helps to keep nutrients near the surface and uses much less diesel.



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