Experimenting with biological fertilisation at Farrington Oils

Experimenting with biological fertilisation at Farrington Oils

With mineral fertiliser prices through the roof, many farmers are now considering how to reduce and substitute synthetic fertilisers while maintaining profit margins. AgriCaptureCO2 partner and pilot farm Farrington Oils is a frontrunner in this area. Duncan Farrington is one of the vocal proponents of ‘regenerative agriculture’ in the UK and has dedicated a lot of time and effort to try new approaches to make his farm more economically and environmentally sustainable. One of his most recent experiments was with ‘biological nutrition’.

Substituting nitrogen fertiliser with biological nutrition

In the 2021-2022 growing season, Duncan and his farm’s agronomy consultants worked with Soil Fertility Services Ltd to trial the replacement of (some) synthetic nitrogen fertiliser with a biological nutrition alternative based on liquid worm compost extract. The purpose of this trial was to gather and assess results on both the crop yield and financial performance of this fertilisation programme. 

The trial was done under zero tillage, with untreated winter wheat seeds (no fungicide dressing) planted at 400 seeds per m². Two tramline widths of 24m each were grown under a standard farm practice using normal synthetic nitrogen fertiliser, to serve as a comparison. The wheat was grown with low fungicide use in the trial and in the control plot, as the variety used has excellent disease resistance.

In addition, a series of different products was used throughout the growing season, including biological bacteria as made from compost tea type products, minerals and sugars. For example:

• A consortium of beneficial soil borne bacillus bacteria cultured from native UK strains
• Humic and Fulvic acids with sugars and trace elements
• Nitrogen fixing bacteria

The only difference between the crops other than whether or not they received biological treatment was the total amount of synthetic nitrogen used: 110kg/ha of N in the trial area compared to 220kg/ha N used in the standard farm practice.

Farm staff, Soil Fertility Services, and agronomic consultants took samples from the field throughout the season. These noted that the trial site (with half N application) was consistently lower in Nitrogen content (as would be expected) and could clearly be seen in the colour of the crop. Soil Fertility Services carried our tissue analysis on their product side of the field, but did not do comparison tests on the control aspect. ADAS results from nutrient offtake in the crop shows little difference between the biological and standard farm practice, with grain nitrogen content being lower in the biological. 

Does it pay off?

The cost and financial benefits of such trials depend on fluctuating input and commodity prices, making it impossible to draw a universal conclusion. However, this one-off trial gives a glimpse of the calculations farmers might be making, in a context of high fertilisers and wheat prices.

A total of £117/ha was spent on biological products, while the reduced nitrogen fertiliser application saved £127/ha. According to the combined yield meter in the adjacent plots, the yield difference is estimated to be almost 1 tonne/ha in favour of standard farm practice. At current wheat prices, this equates to around £236/ha difference. However, it was felt that the difference over the whole field may have been less, at perhaps 500kg/ha difference, or £118/ha. This disparity is attributable to varying soil type across the field, as the soil improves in quality in the valley with a lower clay, higher silt content and no doubt higher carbon content. In this part of the field, yields exceeded 12 tonnes/ha. 

It is unknown from this trial, what effect any potential residual nitrogen has in the soil from previous crops and whether this would reduce over time, making the differences in performance more noticeable. The trial will be repeated on the same field for the 2023 harvest, using the same tramlines in a crop of spring barley to investigate further.

In terms of crop quality, some visual differences were observable, especially around ear emergence, with the biologically treated crop producing a lighter colour. Tests are ongoing to analyse the nutritional content of crops from the trial and control plots. Any difference here, for example higher protein content in the biologically treated crops, would be significant, as it could also affect potential quality premiums and financial performance. 

Climate benefits

In addition to yield and financial outputs, Farrington Oils investigated the difference in greenhouse gas emissions between the two programmes, in collaboration with One Carbon World, another AgriCaptureCO2 partner. The results below show the emissions savings linked to reduced N fertiliser use. These figures are not a comprehensive GHG budget for the trial, however, as emissions linked to the production and transport of the biological treatment are not considered, and neither are differences in soil carbon sequestration (which would require a much longer trial period to be measured). 

The biological products are based on liquid worm compost extract, therefore compared to the Haber Bosch process for manufacturing synthetic nitrogen, these products would have a small emission footprint. There will however be Scope 3 emissions from transportation to the farm. The manufacturer of the biological products tends to say that they are adding carbon to the soil when using these products as they contain humic and fulvic carbon compounds.

*On-farm Emissions – these are related to the nitrous oxide emissions that occur within the boundary of the farm.

*Off-farm Emissions – these are related to the production of the fertilisers themselves so are indirect emissions.

The early verdict

While results have not yet been finalised and this is only a single trial hence not entirely conclusive, some lessons can already be drawn. The field trial results show that synthetic nitrogen can successfully be reduced with a relatively minor loss in yield but significant benefits for GHG emissions. The financial balance is highly dependent on fertiliser prices and wheat prices, with the balance currently negative, although this is likely to change over time. 

Taking GHG emissions into account changes the whole yield/financial/GHG balance: the biological treatment shows clear advantages, though at a net cost for farmers in current circumstances. This highlights the need for policy support or other financial rewards to compensate farmers for the increased costs of sustainable farming practices, for example payments for regenerative practices considering potential GHG emissions reduction and increase in overall soil health.

Another early lesson was that the underlying soil type appeared to have a stronger impact on crop performance than the type of added nutrition used. This is not so surprising, as soil health plays a major role in crop performance, hence improving this should be seen as the first step towards sustainable farming techniques, above trying to find a ‘silver bullet’ quick-fix approach such as simply swapping one type of fertiliser for another.