Cultivations and Carbon

Cultivations and Carbon

Capturing value from the 10-year Traffic & Tillage Project at Harper Adams


The long-term programme of Traffic & Tillage research at Harper Adams University started in 2010 with the first experimental crop harvested in 2012 and has been the “field laboratory” for three successful doctoral graduates (Emily Smith, Anthony Millington and Magdalena Kaczorowska-Dolowy).

This is a long-term internationally unique study focusing on soil management techniques where the interaction between traffic management practices and different tillage practices are considered. It resulted as a direct output from the formation of the industry led (coordinated by Agrii) Soil and Water Management Centre at Harper Adams University with scholarship funding and in-kind support from, The Morley Agricultural Foundation , Douglas Bomford Trust, Michelin, Vaderstad, AGCO and Harper Adams University.

The research started with an initial focus on the soil physical conditions, yield and the cost/benefits of the effects of three traffic management systems imposed on a sandy loam soil:

  1. standard inflation pressure tyres (STP)
  2. low tyre (high flexion) inflation pressure tyres (LTP) and
  3. controlled traffic farming (CTF)

on soils managed with three tillage treatments:

  1. deep (25 cm),
  2. shallow (10 cm) and
  3. no-till

for a winter wheat/winter barley/spring oats/winter field beans crop rotation.



Figure 1 - a) Experimental design map showing the distribution of the blocks and plots and the different traffic and tillage treatments. b) Aerial photo of Marge Marsh field.


More recently, in addition to maintaining the monitoring of soil physical conditions and crop responses, the focus moved to studying soil biological and health condition and is now focusing on soil carbon sequestration.

The results of the continuing long-term study have shown that the effect of both traffic management and tillage systems can have significant effects on the crop yield and farm economy together with soil biology and health.


Key messages on crop yields:


  1. Deep tillage gives no yield advantage over shallow tillage.
  2. Shallow tillage gives the best compromise between yield and soil structure.
  3. Zero tillage produces lower yields initially, though yield recovers over time (7-8 years) as the soil structure develops.
  4. Rotations need to be adjusted to manage crop residues to optimize zero tillage systems.
  5. The benefits of mitigating traffic (low pressure tyres and CTF) appeared from the start of the system and are consistent over time.
  6. Deep tilled soil benefits the most from traffic mitigation, indicating that loosening and re-compaction causes the most damage to soils.
  7. Zero tilled soils show the least response to traffic mitigation, indicating that they are more resilient to traffic.



Figure 2: Samples from CTF zero tillage (left, not tilled for 10 years) and CTF deep tillage (right, tilled down to 250mm for 10 years) showing very little difference in crop growth and large differences in soil structure, its stability and resilience (zero tillage) vs weak and loose soil at high risk of soil damage (deep tillage).


Key messages on soil carbon:


Soil organic carbon (SOC) is a component of soil organic matter (SOM). There has been growing interest in soil carbon dynamics in recent years. Many agricultural soils have reduced SOM and so, it is argued, they likely have the potential to sequester carbon through building SOM. Different soil management practices have different impacts on SOM dynamics and so total soil carbon stocks.


The results from our field experiment to date have shown that:

  1. Tillage had a strong effect on total carbon (C) stocks, with soils under Zero tillage storing 5 t/ha more than Shallow and Deep tillage treatments on average at 0-30 cm depth.  
  2. The highest total C stocks were observed in Zero tillage CTF (89.0±4.2 t/ha), followed by Zero tillage LTP (85.3±4.1 t/ha). The lowest total C stocks were observed in Shallow and Deep tillage both in CTF treatments (70.0±4.0 t/ha and 70.1±4.3 t/ha respectively). 


These results confirm that soils have different levels of potential to store carbon dependent on management, with almost 20 t/ha of C stored more under the optimum management practice compared to the most detrimental practice. This leads to the obvious question as to how or why more C is stored under some treatments than others.



The next steps of the project


Ana Prada (PhD student, apradabarrio[at] will investigate this by using natural abundance C12/C13 stable isotope probing. By growing millet, a C4 plant, in soils where only C3 plants have been grown previously, it will be possible to trace the flow of C from the plants into the different organic matter fractions. These have different turnover times and dynamics within the soil and so this investigation will provide insights into the mechanisms that determine the residence time of C in soils. This will help inform as to best practices for maximising C sequestration into soils thereby improving soil health and helping to help mitigate climate change.