Field operations are the next most significant source of GHG emissions. This is both because of the effect cultivations have on the soil and also because of the fuel use and wear and tear involved with cultivation.
There is a growing body of evidence that demonstrates the fewer the number of passes and the less the disturbance to the soil with each pass, the lower the GHG emissions are from the soil.
GHG emissions from the soil occur as Carbon Dioxide (CO2) and to a lesser extent methane (CH4) as well as N2O.
This is principally as a result of the oxidation of the soil organic matter (SOM) by microbial activity that is stimulated by available oxygen following a mechanical cultivation.
Reducing the frequency and intensity of cultivations results in less SOM being oxidised which, combined with the potential improvement in the soil structure from increasing SOM, is a clear management strategy for reducing GHG emissions from arable crops. There is a strong correlation between increasing SOM in the crop rooting zone and increasing yields.
The UK soil survey estimated that between 1978 and 2003, soil carbon (the principle chemical of soil organic matter) declined by an average of 0.6% in cropped soils. The Countryside Survey records that, between 1978 and 2007, the topsoil carbon concentration in arable soils fell by 11%. The bulk of this reduction was observed between 1998 and 2007 (Parliment, 2016).
It has been estimated that this would be reversed by a zero tillage system and could be substantially mitigated by reduced tillage systems compared to traditional ploughing and power harrowing. However, there is some evidence that where reduced cultivations result in higher soil moisture contents, there can be correspondingly higher N₂O emissions. As well as this, rising global temperatures can influence the behaviour and activity of respiring micro-organisms, resulting in an increase in CO2 and N2O emissions.
There are a number of organisations in the UK that provide specialist support for zero and min till systems, search online for more details
As with all agricultural production, any system of crop production will result in inevitable GHG emissions from various parts of the production process. Ensuring that all aspects of the growing process are working to their optimum will allow the crop to yield to its potential, whatever growing system is chosen.
Attention to soil management and soil structure is fundamental for all growing systems, and also drainage where appropriate. Eliminating the potential for any soil erosion through cultivation and cropping techniques is fundamental to good husbandry and long term cropping. See the 'Soil management' section of the Toolkit for more details.
Ensuring that nutrient supply to the crop is adequate across all nutrients, so a restriction of a single element is not throttling the yield potential is important, as is ensuring that the soil has a suitable pH (around 6.3 for most arable crops).
Looking after the crop to reduce competition from weeds, pests and pathogens is obvious.
Cover cropping/catch cropping is a technique used to both build SOM and also to scavenge for nutrients after the crop has finished its growth phase and for building fertility through nitrogen fixing. There are a number of forums and advisors in this area and it is likely to become more common place on efficient arable farms in the future.
Organic materials – see the Soil section of the toolkit for more information on the benefits of addition of organic materials, including crop residues, to the soil.
Looking after machinery, both working and static to ensure that it is working to its optimum and suitably matched to the operation required provides further areas for improving the farm's carbon footprint in a very direct and easily quantifiable way. See the 'Buildings and Operations' section of the toolkit.
This attention to detail also directly benefits the profitability of the overall operation.