Soil health improvements gather pace at Lamport
The beneficial effects of reduced tillage and cover crops on soil organic carbon content are becoming increasingly apparent after five years of studies on a heavy soil site in Northamptonshire.
A series of fully replicated trials on difficult silty clay loam soil at Agrovista’s Lamport AgX trials site has identified a range of statistically significant changes in the biological, physical and chemical make-up of the soil, which has helped improve soil health and drive carbon sequestration.
Dr. David Purdy, John Deere’s East Anglia territory manager, who is carrying out the research, said: ”We firmly believe that good soil health starts with good photosynthesis.
“We know that healthy plants make healthy soils, not the other way round. When you have a very healthy plant in a very healthy soil, one and one don’t make two – they make a multiple of that, bringing all manner of benefits.
“So the main focus of these trials is to investigate how can we maximise a production system to get as much energy in the form of photosynthesis into our soils.”
Using cover crops in addition to cash crops is key. “By adding a cover crop we are capturing sunlight throughout the season,” David said. “An autumn cover crop/spring cropping sequence is sequestering carbon through the production cycle, whereas spring cropping on its own does not.
“As a result, soil biology has undergone a significant change over the past five years. We have seen a large increase in microbial biomass – phospho-lipid fatty acid (PLFA) production, soil respiration and rate of decomposition have all have gone up statistically.
“Some went up early in the trials period, others only this year, but all the numbers are starting to correlate. We have also seen big changes in worm numbers, which has greatly improved water infiltration rates, which improves soil workability and timeliness of operations.
“We are now driving the biology in this soil pretty hard, and we’re starting to see some really significant changes in our soils in years four and five.”
Provided cover crops are sown in good time it is possible to produce up to 6t/ha of biomass, depending on species (figure 1). About half of that is carbon.
“You have to plant covers early to drive this,” David said. “After mid-August there is a big fall-off in the three species we looked at. We will be testing others in the future.”

Figure 1.

Putting energy into soils and driving biology is delivering better physical results too. “Soil structure in particular has been a really interesting journey,” David said. “Bulk density has dropped due to the increase in soil carbon and we’ve negated the need for deep cultivations unless we damage the soil.
“Five years ago the soil was formed of big, lumpy blocks across these trials. After the end of year 4, we were seeing some big differences between plots (figure 2).
Figure 2.

“The control plot, which was no tillage/no cover crops, in the fourth year started to change due to natural processes, and has started to break down more easily.
“The subsoiling plots, which have been worked to 25cm depth each season, are now big lumps of wet mass – we’ve really denatured it. So deep tillage is causing a huge degree of problems with soil structure.”
David has also studied soil chemistry extensively at different depths. “It’s a difficult one, but suffice to say our cover crop systems have stabilised electro-conductivity at between 0.4 and 0.8, increased soil nitrogen and done all sort of positive things with different elements.”
After five years the no-till/cover crop plots have significantly higher levels of soil organic matter than the other systems (figure 2), apart from the field margin, which contains 8.6% SOM.
“This shows the soil in the field is capable of carrying a lot more carbon,” David notes. “Put another way, over 50 years we’ve managed to burn off a lot of organic matter in our soils.”
Carbon opportunity
As far as carbon goes, the field margin contained 203t/ha to a depth of up to 1m, whilst the rest of the field was well below that, indicating the potential for improvement. “There’s lots of opportunity to bury more carbon in our soils,” David said.
Overall, no-till cover crop treatments have significantly increased soil carbon stocks (SOM x soil bulk density x depth of core) at 15-30cm depth (figure 3) . Conversely, subsoiling treatments significantly reduced carbon stocks at 0-15cm depth (figure 4).
“We increased carbon in our no-till/cover crop plots to 44t/ha, compared with our no till/no cover plots at 36t/ha. So in five years, we’ve put 27t/ha of CO2 equivalent into this area of our soils.
“In the tillage plots, we are down to 47t/ha of carbon, compared with 52t/ha for all the no-till plots, so we’ve burnt 17t/ha of CO2 equivalent in five years, which is quite alarming – we are doing quite a lot of damage to carbon.
“Our cover crop system is very low-cost that buries carbon as well. We will continue to fine tune it and look at it from a rotational point of view, but we are now really seeing the potential of cover crops to sequester carbon, and the figures show there’s lots of opportunity to do this.”
Figure 3.

Figure 4.
